Reducing Urban Heat Islands: Compendium of Strategies Cool Pavements
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Acknowledgements Reducing Urban Heat Islands: Compendium of Strategies describes the
causes and impacts o summertime urban heat islands and promotes strategies or lowering temperatures in U.S. communities. This compendium was developed developed by the Climate Protection Partnership Division in the U.S. Environmental Protection Agency’s Oce o Atmospheric Programs. Eva Wong managed its overall development. Kathleen Hogan, Julie Rosenberg, Neelam R. Patel, and Andrea Denny provided editorial support. Numerous EPA sta in oces throughout the Agency contributed content and provided reviews. Subject area experts rom other organizations around the United States and Canada also committed their time to provide technical eedback. Under contracts 68-W-02-029 and EP-C-06-003, Perrin Quarles Associates, Inc. provided technical and administrative support or the entire compendium, and Eastern Research Group, Inc. provided graphics and production services. For the Cool Pavements chapter, Cambridge Systematics, Inc. provided support in preparing a June 2005 drat report on cool pavements under contract to EPA as part o EPA’s Heat Island Reduction Initiative. Experts who helped shape this chapter include: Bruce Fergus Ferguson, on, Kim Fisher, Jay Golden, Lisa Hair, Liv Haselbach, David Hitchcock, Kamil Kaloush, Mel Pomerantz, Nam Tran, and Don Waye.
Contents Cool Pavements 1 1 1. How It Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 3 1.1 Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 5 1.2 Solar Reectance (Albedo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 1 . 3 T h e r m a l E m i t t a n c e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 6 1.4 Pe Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 8 1.5 Other Factors to Consider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 1.6 Te Temperature Eects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 10 2. Potential Cool Pavement Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 11 3. Benets and Costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 23 3.1 Benets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 23 3.2 Costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2 . 5 3.3 Be Benet-Cost Co Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 26 4. Cool Pavement Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 26 5. Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3 . 0 Endnotes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3. 1
Cool Pavements
C
ool pavements reer to a range o established and emerging materials. These pavement technologies tend to store less heat and may have lower surace temperatures compared with conventional products. They can help address the prob lem o urban heat islands, which result in part rom the increased temperatures o paved suraces in a city or suburb. Commu nities are exploring these pavements as part o their heat island reduction eorts. Conventional pavements in the United States are impervious concrete* and asphalt, which can reach peak summertime surace tem peratures o 120–150°F (48–67°C). 2 These suraces can transer heat downward to be stored in the pavement subsurace, where it is re-released as heat at night. The warmer daytime surace temperatures also can heat stormwater as it runs o the pavement into local waterways. These eects contribute to urban heat islands (especially at nighttime) and impair water quality.
In many U.S. cities, pavements represent the largest percentage o a community’s land cover, compared with roo and vegetated suraces. As part o EPA’s Urban Heat Island Pilot Project, Lawrence Berkeley National Laboratory (LBNL) conducted a series o urban abric analyses that provide baseline data on land use and land use cover, including paved sur aces or the pilot program cities. 1 Figure 1 shows the percent o paved suraces in our o these urban areas, as viewed rom below the tree canopy. The data are rom 1998 through 2002, depending on the city. Paved areas, which can absorb and store much o the sun’s energy contributing to the urban heat island eect, accounted or nearly 30 to 45 percent o land cover.
Figure 1: Paved Surace Statistics or Four U.S. Cities Salt Lake City
Sacramento
Houston
Chicago
0
5
10
15
20
25
30
35
40
Percent Coverage
* When new, concrete has a high solar reectance and generally is considered a cool pavement; however, it loses reectance over time, as discussed in Section 1.2.
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1
45
50
Figure 2: Conventional Pavement Temperatures a v o n n I T R A M S n y t o i e s c r e n i e v l l n e U c x e E t a t o S r a e t n o n z e i C r l A a t n a o s i t n a o N i t
This picture o Phoenix, Arizona, in the summer shows a variety o conventional pavements that reached temperatures up to 150°F (67°C).
Defning Cool Pavements Unlike a “cool” roo, a “cool” pavement has no standard, ocial denition. Until recently, the term has mainly reerred to refective pavements that help lower sur ace temperatures and reduce the amount o heat absorbed into the pavement. With the growing interest and application o permeable pavements—which allow air, water, and water vapor into the voids o a pavement, keeping the material cool when moist—some practitioners have expanded the denition o cool pavements to include permeable pavements as well. Ongoing permeable pavement research is im portant because these systems, compared with conventional pavement systems, react dierently and lead to dierent environmental impacts. Further, as we understand better how pavements aect urban climates and develop newer, more environmen tal technologies, additional technologies that use a variety o techniques to remain cooler are likely to emerge. As concerns about elevated summertime temperatures rise, researchers and policymakers are directing more attention to the impact pavements have on local and global climates. This chapter discusses: •
•
Pavement properties and how they can be modied to reduce urban heat islands Conditions that aect pavement proper ties
•
Potential cool pavement technologies
•
Cool pavement benets and costs
2
•
•
Cool pavement initiatives and research e orts Resources or urther inormation.
Given that cool pavements are an evolv ing technology and much is still unknown about them, this compendium presents basic inormation to give readers a general understanding o cool pavement issues to consider; it is not intended to provide decision guidance to communities. Deci sion-makers can work with local experts to obtain location-specic inormation to
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Why Have Communities Promoted Cool Roos More Than Cool Pavements? A ew decades ago when the concept o using cool roos and pavements emerged, researchers ocused on radiative properties—surace solar refectance and thermal emittance—associated with these technologies. Scientists, engineers, and others worked together through the standards-development organization ASTM Interna tional to create test standards or these properties that could apply to both roos and pavements. (See Section 4.1.) While researchers, industry, and supporters o energy eciency have helped advance cool roong into the market, cool pavement has lagged behind. Three actors, which dierentiate pavements rom roos, may contrib ute to this dierence: 1. Pavements are complex. Conditions that aect pavement temperatures, but not roong materials, include: (a) dirtying and wearing away o a surace due to daily oot and vehicle trac, aecting pavement surace properties; (b) convection due to trac movement over the pavement; and (c) shading caused by people and cars, vegetation, and neighboring structures and buildings. These actors are discussed in Sections 1.2 and 2. 2. Pavement temperatures are aected by radiative and thermal characteristics, un like cool roos, where radiative properties are the main concern. This is discussed in Section 1.3. 3. Pavements serve a variety o unctions throughout an urban area. Their uses range rom walking trails to heavily tracked highways (unlike cool roos, which generally perorm the same unction and are o-the-shel products). Dierent materials and specications are needed or these dierent uses, and pavements are oten individually specied, making it dicult to dene or label a cool pave ment. urther guide them in the pavement selec tion process. EPA expects that signicant ongoing research eorts will expand the opportunities or updating existing technol ogies and implementing new approaches to cool pavements. At the end o Sections 4 and 5 in this document, organizations and resources with the most recent inormation are listed. Communities will also continue to implement new demonstration projects and cool pavement initiatives. EPA intends to provide updated inormation as it be comes available. Please visit < www.epa. gov/heatisland/index.htm>.
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1 How It Works Understanding how cool pavements work requires knowing how solar energy heats pavements and how pavement infuences the air above it. Properties such as solar energy, solar refectance, material heat capacities, surace roughness, heat transer rates, thermal emittance, and permeability aect pavement temperatures.
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Reducing or Shading Pavements Some eorts have emerged that ocus on reducing the need to pave, particularly over vegetated areas that provide many benets, including lowering surace and air tem peratures. Communities have used various options to reduce the amount o paved surace areas, such as lowering parking space requirements, connecting parking and mass transit services, allowing or narrower street widths, or providing incentives or multi-level parking versus surace lots. 3 Concerned communities that move orward with paving oten shade it with vegeta tion. The “Trees and Vegetation” chapter discusses the use o measures such as park ing lot shading ordinances as part o a heat island mitigation strategy. Another option some local governments and private rms are considering involves installing canopies that incorporate solar panels in parking lots. These photovoltaic canopies shade suraces rom incoming solar energy and generate electricity that can help power nearby buildings or provide energy or plug-in electric vehicles. 4 For more inormation on urban planning and design approaches to minimize paved suraces, see < www.epa.gov/smartgrowth>, and or inormation on vegetated sur aces, see the “Trees and Vegetation” chapter o this compendium.
Figure 3: Solar Energy versus Wavelength Reaching Earth’s Surace on a Typical Clear Summer Day 1.00 0.90
y t i s n e t n I r a l o S d e z i l a m r o N
ultraviolet
visible
infrared
0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0
200
400
600
800
1000 1200 1400 1600 1800 2000 2200 2400 2600
Wavelength (in nanometers) Solar energy intensity varies over wavelengths rom about 250 to 2,500 nanometers. Figure 3 demonstrates this variation, using a normalized measure o solar intensity on a scale o zero (minimum) to one (maximum). Currently, reective pavements are light colored and primarily reect visible wavelengths. However, similar to trends in the roong market, researchers are exploring pavement products that appear dark but reect energy in the near-inrared spectrum. 5 (See the “Cool Roos” chapter o the compendium or more inormation.)
4
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1.1 Solar Energy Solar energy is composed o ultraviolet (UV) rays, visible light, and inrared en ergy, each reaching the Earth in dierent percentages: 5 percent o solar energy is in the UV spectrum, including the type o rays responsible or sunburn; 43 percent o solar energy is visible light, in colors rang ing rom violet to red; and the remaining 52 percent o solar energy is inrared, elt as heat. Energy in all o these wavelengths contributes to urban heat island ormation. Figure 3 shows the typical solar energy that reaches the Earth’s surace on a clear summer day.
Most existing research on cool pave ments ocuses on solar refectance, which is the primary determinant o a material’s maximum surace tem perature. Many opportunities exist to improve this property in pavements. (See Table 2, beginning on page 15.)
Figure 4: Typical Solar Reectance o Conventional Asphalt and Concrete Pavements over Time 45 40
1.2 Solar Reectance (Albedo) Solar refectance, or albedo, is the per centage o solar energy refected by a surace. Most research on cool pavements has ocused on this property, and it is the main determinant o a material’s maximum surace temperature.6 Albedo also aects pavement temperatures below the surace, because less heat is available at the sur ace to then be transerred into the pave ment. Researchers, engineers, and industry have collaborated to develop methods to determine solar refectance by measuring how well a material refects energy at each wavelength, then calculating the weighted average o these values. * (See Table 1 on page 7.) Conventional paving materials such as as phalt and concrete have solar refectances o 5 to 40 percent, which means they absorb 95 to 60 percent o the energy reaching them instead o refecting it into the atmo sphere. (See Figure 4.) However, as Figure 4 also shows, these values depend on age and
% n 35 i e c n 30 a t c e 25 fl e r r 20 a l o S 15
Concrete pavements
Asphalt pavements
10 5 0 1
2
3
4
5
6
Due to weathering and the accumulation o dirt, the solar reectances o conventional asphalt and concrete tend to change over time. Asphalt consists largely o petroleum derivatives as a binder mixed with sand or stone aggregate. Asphalt tends to lighten as the binder oxidizes and more aggregate is exposed through wear. Concrete also uses sand and stone aggregate, but in contrast to asphalt, typically uses Portland cement as a binder. 7 Foot and vehicle trafc generally dirty the cement causing it to darken over time.
material, and thus usually change over time. Figure 5 shows how changing only albedo can signicantly alter surace temperatures. Although researchers, including those at LBNL, have made light-colored pavements with solar refectances greater than 75 per cent,8 these high albedo pavements do not have widespread commercial availability.
* Albedo is typically measured on a scale o zero to one. For this compendium, albedo is given as a percentage, so an albedo o 0.05 corresponds to a solar reectance o 5 percent. The “solar reectance index” is a value on a scale o zero to 100 that incorporates both solar reectance and thermal emittance in a single measure to represent a material’s temperature in the sun. (See Table 1 on page 7 or urther explanation.)
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Figure 5: The Eect o Albedo on Surace Temperature
e c n e l l e c x E o r e t n e C l a n o i t a N U S A
Albedo alone can signicantly inuence surace temperature, with the white stripe on the brick wall about 5–10°F (3–5°C) cooler than the surrounding, darker areas.
1.3 Thermal Emittance A material’s thermal emittance determines how much heat it will radiate per unit area at a given temperature, that is, how readily a surace sheds heat. Any surace exposed to radiant energy will heat up until it reaches thermal equilibrium (i.e., gives o as much heat as it receives). When exposed to sun light, a surace with high emittance will reach thermal equilibrium at a lower tem perature than a surace with low emittance, because the high-emittance surace gives o its heat more readily. As noted in Table 1 on page 7, ASTM methods can be used to measure this property.
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Thermal emittance plays a role in determin ing a material’s contribution to urban heat islands. Research rom 2007 suggests albedo and emittance have the greatest infuence on determining how a conventional pave ment cools down or heats up, with albedo having a large impact on maximum sur ace temperatures, and emittance aecting minimum temperatures.9 Although thermal emittance is an important property, there are only limited options to adopt cool pave ment practices that modiy it because most pavement materials inherently have high emittance values.10
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Standards or Measuring Solar Reectance and Thermal Emittance To evaluate how “cool” a specic product is, ASTM International has validated labo ratory and eld tests and calculations to measure solar refectance, thermal emit tance, and the solar refectance index, which was developed to try to capture the eects o both refectance and emittance in one number. (See Table 1 below.) Labo ratory measurements are typically used to examine the properties o new material samples, while eld measurements evaluate how well a material has withstood the test o time, weather, and dirt. The nal method listed in Table 1 is not an actual test but a way to calculate the “solar refectance index” or SRI. The SRI is a value that incorporates both solar refec tance and thermal emittance in a single value to represent a material’s temperature in the sun. This index measures how hot a surace would get compared to a standard black and a standard white surace. In physical terms, this scenario is like laying a pavement material next to a black surace and a white surace and measuring the temperatures o all three suraces in the sun. The SRI is a value between zero (as hot as a black surace) and 100 (as cool as a white surace). Table 1: Solar Reectance and Emittance Test Methods Property Solar reectance
Test Method
Equipment Used
ASTM E 903 - Standard Test Method
Integrating sphere spectro
or Solar Absorbance, Reectance,
photometer
Test Location Laboratory
and Transmittance o Materials Using Integrating Spheres. Solar reectance
ASTM C 1549 - Standard Test Method
Portable solar reectometer
or Determination o Solar Reectance
Laboratory or eld
Near Ambient Temperature Using a Portable Solar Reectometer Solar reectance
ASTM E 1918 - Standard Test Method
Pyranometer
Field
or Measuring Solar Reectance o Horizontal and Low-Sloped Suraces in the Field Total emittance
ASTM E408-71 - Standard Test Methods Portable, inspection-meter or Total Normal Emittance o Suraces
Laboratory or
instruments
eld
None (calculation)
—
Using Inspection-Meter Techniques Solar reectance
ASTM E 1980 - Standard Practice or
index
Calculating Solar Reectance Index o Horizontal and Low-Sloped Opaque Suraces
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Pavement Surace and Subsurace Temperatures This chapter mainly ocuses on pavement surace temperatures, as most o the cited studies ocus on the surace layer. For conventional pavements, most o the impacts at the surace tend to aect the subsurace similarly. For example, conventional pavements with high solar refectance generally reduce surace and subsurace tem peratures, as less heat is available at the surace to absorb into the pavement. How ever, permeable suraces react dierently. When dry, permeable pavement surace temperatures may be higher than their impermeable equivalent; but preliminary research shows that the subsurace generally is similar to or even cooler than the conventional equivalent, because the permeable layer reduces heat transer below. 11 More inormation on subsurace heat transer is needed to understand the potential heat island impacts because the heat stored in the subsurace may signicantly a ect nighttime temperature. Still, many complex interactions take place between the surace and subsurace layers. These interactions are either briefy covered in Section 1.5 or beyond the scope o this chapter.
1.4 Permeability Although originally designed or storm water control, permeable pavements are emerging as a potential cool pavement. These pavements allow air, water, and water vapor into the voids o the pavement. Permeable pavement technologies include porous asphalt applications, pervious con crete applications, permeable pavers, and grid pavements. To achieve both perme ability objectives and structural needs or expected trac load, these permeable pavements benet rom proper design and installation.12 When wet, these pavements can lower tem peratures through evaporative cooling. The water passes through the voids and into the soil or supporting materials below. (See Fig ure 6.) Moisture within the pavement struc ture evaporates as the surace heats, thus drawing heat out o the pavement, similar to evaporative cooling rom vegetated land cover. Some permeable pavement systems
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Figure 6: Permeable versus Conventional Asphalt
e r u t l u c i r g A o t n e m t r a p e D . S . U
Permeable asphalt (oreground) allows water to drain rom the surace and into the voids in the pavement, unlike conventional asphalt (mid- and background).
contain grass or low-lying vegetation, which can stay particularly cool because the sur ace temperature o well-hydrated vegeta tion typically is lower than the ambient air temperature.
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When dry, the extent to which permeable pavements can infuence temperatures is more complex and uncertain. For example, the larger air voids in permeable pave ments increase the available surace area. These conditions may limit heat transer to the lower pavement structure and soils, keeping heat at the pavement’s surace (and increasing daytime surace tempera tures), but reducing bulk heat storage (re ducing release o heat at nighttime). 13 The larger surace area also may help increase air movement—convection—over the pave ment, transerring heat rom the pavement to the air. Overall, the limited transer o heat to the pavement subsurace layers would reduce the release o heat during the nighttime. Release o stored heat rom urban materials is a signicant contributor to the nighttime heat island experienced in many cities.
Water Retentive Pavements and Water Sprinkling in Japan Some cities in Japan, such as Tokyo and Osaka, are testing the eectiveness o water retentive pavements as part o using permeable pavements to reduce the heat island eect. These porous pavements can be asphalt or concrete-based and have a sublayer that consists o water retentive materials that absorb moisture and then evaporate it through capillary action when the pavement heats up. Some o these systems involve underground water piping to ensure the pavement stays moist. Researchers have also tested water sprinkling, where pavements are sprayed with water during the day. Some cities have used treated wastewater. Results to date are promising, as both water retentive pavements and water sprinkling have been eective in keeping pavement temperatures low.14
More research is needed to better under stand the impacts o permeable pavement on air temperatures and urban heat island conditions. Given the complexity o these cooling mechanisms, and the wide range o conditions under which these pavements unction, urther eld testing and valida tion would help to quantiy and clariy the range o impacts and benets o permeable pavements on urban climates.
1.5 Other Factors to Consider Pavement temperatures depend on a series o actors. Refective pavements increase the albedo o the surace to limit heat gain, whereas permeable pavements permit evaporative cooling when the pavement is moist, helping to keep it cool. As shown in Table 2 (beginning on page 15), however, actual conditions alter pavement proper ties, resulting in pavements that may not be “cool” under all circumstances. This chapter presents these issues or communities to consider when making pavement choices.
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Besides solar refectance, emittance, and permeability, other properties and actors infuence how readily pavements absorb or lose heat. •
Convection. Pavement transers heat to
the air through convection as air moves over the warm pavement. The rate o convection depends on the velocity and temperature o the air passing over the surace, pavement roughness, and the total surace area o the pavement exposed to air. Some permeable pave ments have rougher suraces than con ventional pavements, which increases
9
their eective surace area and creates air turbulence over the pavement. While this roughness can increase convection and cooling, it may also reduce a sur ace’s net solar refectance. •
Thermal Conductivity. Pavement with
low thermal conductivity may heat up at the surace but will not transer that heat throughout the other pavement layers as quickly as pavement with higher conductivity. •
Heat Capacity. Many articial materi
als, such as pavement, can store more heat than natural materials, such as dry soil and sand. As a result, built-up areas typically capture more o the sun’s energy—sometimes retaining twice as much as their rural surroundings dur ing daytime.15 The higher heat capacity o conventional urban materials con tributes to heat islands at night, when materials in urban areas release the stored heat. •
Thickness. The thickness o a pave
ment also infuences how much heat it will store, with thicker pavements stor ing more heat.16 •
Urban Geometry. The dimensions and
spacing o buildings within a city, or ur ban geometry, can infuence how much heat pavements and other inrastruc ture absorb. For example, tall buildings along narrow streets create an “urban canyon.” (See Figure 7.) This canyon e ect can limit heat gain to the pavement during the day, when the buildings pro vide shade. But these same buildings may also absorb and trap the heat that is refected and emitted by the pave ment, which prevents the heat rom escaping the city and exacerbates the heat island eect, especially at night. The overall impact o the urban canyon eect will depend on how a specic city is laid out, the latitude, the time o year, and other actors. 10
More research is needed to determine the exact impacts these properties have on pavement temperatures and the urban heat island eect.
1.6 Temperature Eects Solar refectance and thermal emittance have noticeable eects on surace tempera tures, as discussed in Sections 1.2 and 1.3. Depending on moisture availability, perme able pavements also can lower pavement temperatures. Other properties, as noted in Section 1.5, also infuence pavement sur ace and subsurace temperatures through a variety o complex interactions. In gener al, lower surace temperatures will result in lower near-surace air temperatures, with the eect decreasing as one moves arther away rom the surace due to air mixing. Location-specic conditions, such as wind speed and cloud cover, can greatly infu ence surace and air temperatures. Currently, ew studies have measured the role pavements play in creating urban heat islands, or the impact cooler pavements can have on reducing the heat island e ect. Researchers at LBNL, however, have estimated that every 10 percent increase in solar refectance could decrease sur ace temperatures by 7ºF (4ºC). Further, they predicted that i pavement refec tance throughout a city were increased rom 10 percent to 35 percent, the air temperature could potentially be reduced by 1ºF (0.6ºC).17 Earlier research analyzed a combination o mitigation measures in the Los Angeles area, including pavement and roong solar refectance changes, and increased use o trees and vegetation. The study identied a 1.5ºF (0.8ºC) temperature improvement rom the albedo changes.18 A subsequent report analyzed the monetary benets associated with these temperature improvements, and estimated the indirect benets (energy savings and smog reduc tions) o the temperature reduction in Los RedUcING URBAN HeAt IslANds – dRAFt
Figure 7: Urban Canyons
r e i e M k r a M
The row o three- and our-story townhouses on the let creates a relatively modest urban canyon, while the skyscrapers on the right have a more pronounced eect.
Angeles rom pavement albedo improve ments would be more than $90 million per year (in 1998 dollars).19
2 Potential Cool Pavement Types Current cool pavements are those that have increased solar refectance or that use a permeable material. Some o these pave ments have long been established—such as conventional concrete, which initially has a high solar refectance. Others are emerging—such as microsuracing, which is a thin sealing layer used or mainte nance. 20 Some pavement applications are or new construction, while others are used or maintenance or rehabilitation. Not all applications will be equally suited to all cOOl PAVeMeNts – dRAFt
uses. Some are best or light trac areas, or example. Further, depending on local conditions—such as available materials, labor costs, and experience with dierent applications—certain pavements may not be cost eective or easible. Generally, decision-makers choose pav ing materials based on the unction they serve. Figure 8 shows the proportions o pavement used or dierent purposes in our cities. Parking lots typically make up a large portion o the paved suraces in urban areas. All current cool pavement technologies can be applied to parking lots, which may explain why many re search projects have been and are being conducted on them. 11
Figure 8: Percentage o Pavement Area by Type o Use21
•
contain voids and are designed to allow water to drain through the surace into the sublayers and ground below. These materials can have the same structural integrity as conventional pavements. For example, some orms o porous pavements, such as open-graded ric tion course (OGFC) asphalt pavements, have been in use or decades to improve roadway riction in wet weather.22 Recently, rubberized asphalt has been used on roads and highways to reduce noise, and pervious concrete applications are being studied or road way use. For some permeable pavement options, the typical use may be or lower trac areas such as parking lots, alleys, or trails. Examples o nonveg etated permeable pavements include:
60 50 40 e g a t n e c r e P
Roads Parking
30
Sidewalks 20
Other
10 0 Sacramento
Chicago
Salt Lake City
Houston
Cities
L N B L m o r d e f i d o M
LBNL conducted a paved surace analysis in our cities, dividing the uses into our general categories. Roads and parking lots make up the majority o paved areas.
Below are brie descriptions o potential cool pavements and their typical uses: •
Conventional asphalt pavements,
– Porous asphalt
which consist o an asphalt binder mixed with aggregate, can be modied with high albedo materials or treated ater installation to raise refectance. This material has been applied or de cades in a wide range o unctions rom parking lots to highways. •
•
Other refective pavements, made
rom a variety o materials, are mostly used or low-trac areas, such as side walks, trails, and parking lots. Exam ples include: – Resin based pavements, which use clear tree resins in place o petroleum-based elements to bind an aggregate – Colored asphalt and colored concrete, with added pigments or seals to increase refectance
12
– Rubberized asphalt, made by mix ing shredded rubber into asphalt – Pervious concrete – Brick or block pavers, are gener ally made rom clay or concrete, and lled with rocks, gravel, or soil; also available in a variety o colors and nishes designed to increase refectance
Conventional concrete pavements,
made by mixing Portland cement, water, and aggregate, can be used in a wide range o applications including trails, roads, and parking lots.
Nonvegetated permeable pavements
•
Vegetated permeable pavements,
such as grass pavers and concrete grid pavers, use plastic, metal, or concrete lattices or support and allow grass or other vegetation to grow in the inter stices. Although the structural integrity can support vehicle weights compa rable to conventional pavements, these materials are most oten used in areas where lower trac volumes would minimize damage to the vegetation, such as alleys, parking lots, and trails, and they may be best suited to climates with adequate summer moisture.
RedUcING URBAN HeAt IslANds – dRAFt
•
Chip seals consist o aggregate bound
in liquid asphalt, and are oten used to resurace low-volume asphalt roads and sometimes highways. •
Whitetopping is a layer o concrete
greater than 4 inches (10 cm) thick, oten containing bers or added strength. Typical applications include resuracing road segments, intersec tions, and parking lots. •
Ultrathin whitetopping is similar
to whitetopping and can be used in the same applications, but is only 2–4 inches (5–10 cm) thick. •
Microsuracing is a thin sealing layer
used or road maintenance. Light-col ored materials can be used to increase the solar refectance o asphalt. Re searchers recently applied light-colored microsuracing material that consisted o cement, sand, other llers, and a liq uid blend o emulsied polymer resin, and ound the solar refectance to be comparable to that o new concrete. 23 Table 2, beginning on page 15, provides summary inormation or decision-makers to consider. It is meant as a preliminary guide, as more research and locationspecic data are needed. Table 2 includes the ollowing: •
A brie description o the technology
•
The properties associated with it
•
•
•
The potential impacts on pavement and air temperatures Issues to consider Target unctions.
Regarding impacts, the “+” sign indicates a positive eect; or example, a technology generally results in lower pavement tem peratures. A “-” signals a negative eect; or example, a technology may lead to higher air temperatures in certain conditions.
cOOl PAVeMeNts – dRAFt
Slag and Fly Ash Cement Slag and fy ash are sometimes added to concrete to improve its peror mance. Slag is a byproduct o pro cessing iron ore that can be ground to produce cement, and fy ash is a byproduct o coal combustion.24 These materials can make concrete stronger, more resistant to aggressive chemicals, and simpler to place. These cements also reduce material costs and avoid sending wastes to landlls. A key heat island benet o slag is its lighter color, which can increase the refectivity o the nished pavement. A 2007 study measured a solar refec tance o almost 60 percent or cement with slag, versus about 35 percent or a conventional concrete mix. 25 In contrast, fy ash tended to darken con crete unless counterbalanced, such as by added slag. However, substituting fy ash or a portion o the Portland cement reduces greenhouse gases and other emissions associated with pro ducing Portland cement. Because o such benets, Caliornia’s Department o Transportation typically requires use o 25 percent fy ash in cement mixtures.26 Eects described in the table do not con sider magnitude, which may be infuenced by local conditions. Thereore, this inor mation is not intended or comparison. The cool pavement technologies in Table 2 can have positive and negative impacts, depending on actual conditions such as moisture availability and urban design. The points listed under “issues and consid erations” urther illustrate the complexity associated with cool pavements. These bul lets only discuss concerns related to urban
13
heat islands and do not include other local actors or priorities that decision-makers generally consider when making pavement choices. Despite its limitations, Table 2 can be used as a starting point. For example, using Table 2, a city that generally uses asphalt paving can identiy alternative cool as phalt technologies or unctions rom bike trails to roads. They can also discern that high albedo pavements may be most eec tive in open areas, not surrounded by tall buildings. Most communities will urther investigate the benets and costs o the technology, as discussed in Section 3, and location-specic actors, such as political acceptance and experience with the tech nology.
14
Filling in the Gaps As more researchers and communi ties install cool pavement technolo gies, more data will be generated and shared in orums such as the Trans portation Research Board Subcom mittee on Paving Materials and the Urban Climate. (See Section 4 o this chapter.)
RedUcING URBAN HeAt IslANds – dRAFt
c O O l P A V e M e N t s – d R A F t
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications NEW CONSTRUCTION Pavement Type
Description o
Properties to Consider
Technology
Urban Climate Impacts
Impacts
Issues and
Target Use
Considerations
Reective Pavement Options Asphalt pavement,
Asphalt pavements
modied with high
consist o an asphalt
which initially may
temperature because
lower air tempera-
increases over time,
applications, such as
albedo materials or
binder mixed with sand
be 5%, can increase
more o the sun‘s
tures day and night,
and conventional
trails and roads.
treated ater installation or stone, reerred to as
to 15–20% as con-
energy is reected
although air tempera-
asphalt may reach a
• May be most eec
to raise albedo.
ventional asphalt
away, and there is less
tures are not directly
reectance o 20%
tive when paving
ages. 27
heat at the surace to
related to surace
ater seven years. 29
large, exposed areas
absorb into the pave
temperatures and
(See Section 1.2.)
such as parking lots.
ment.
many complicating
aggregate.
• Solar reectance,
• Using light-colored
aggregate, color pig
+ Lowers pavement
+ Can contribute to
ments, or sealants,
actors are involved. 28
the reectance o
– Reected heat can be
• Solar reectance
• Urban geometry,
in particular urban canyons, inuences
conventional asphalt
absorbed by the sides
the impact reective
can be increased.
o surrounding build
pavements have on
• Maintenance ap
ings warming the in
the urban climate.
plications such as
terior o the building
chip seals also can
and contributing to
increase solar reec
the nighttime urban
tance. (See below.)
heat island eect,
• Urban geometry can
1 5
Pavement Temperature
due to the additional
inuence the eect
heat that needs to be
o high albedo pave
released rom urban
ments.
inrastructure.
• Can be used in all
1 6
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) NEW CONSTRUCTION (continued) Pavement Type
Description o
Properties to Consider
Technology
Pavement Temperature
Urban Climate Impacts
Impacts
Issues and
Target Use
Considerations
Reective Pavement Options (continued) Concrete:
Portland cement mixed
•Conventional
with water and ag
• Initial solar reec
•Modied
gregate. Cured until it is
• This can be raised
strong enough to carry
to more than 70%
trafc.
tance can be 40%.
+ Can contribute to
• Solar reectance
• Can be used in all
temperature because
lower air tempera-
decreases over time,
more o the sun’s
tures day and night,
as soiling rom trafc
trails and roads.
energy is reected
although air tempera
darkens the surace.
• May be most eec
using white cement
away, and there is less
tures are not directly
instead o gray ce
heat at the surace to
related to surace
crete may reach a
large, exposed areas,
ment mixtures. 30
absorb into the pave
temperatures and
reectance o 25%
such as parking lots.
• Urban geometry can
inuence the eect o high-albedo pave ments. R e d U c I N G U R B A N H e A t I s l A N d s – d R A F t
+ Lowers pavement
ment.
many complicating actors are involved. – Reected heat can be
• Conventional con
ater 5 years.
31 (See
Section 1.2.) • Urban geometry,
absorbed by the sides
in particular urban
o surrounding build
canyons, inuences
ings warming the in
the impact reective
terior o the building
pavements have on
and contributing to
the urban climate.
the nighttime urban heat island eect, due to the additional heat that needs to be released rom urban inrastructure.
applications, such as
tive when paving
c O O l P A V e M e N t s – d R A F t
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) NEW CONSTRUCTION (continued) Pavement Type
Description o
Properties to Consider
Technology
Pavement Temperature
Urban Climate Impacts
Impacts
Target Use
Considerations
Reective Pavement Options (continued) Other refective
• Resin based pave
• These alternative
+ Lowers pavement
+ Can contribute to
• As with concrete,
• Use depends on the
pavements:
ments use clear
pavements will have
temperature because
lower air tempera-
solar reectance may
pavement applica-
• Resin based
colored tree resins in
varying solar reec
more o the sun’s
tures day and night,
decrease over time
tion. In general,
• Colored asphalt
place o cement to
tances based on the
energy is reected
although air tempera-
as soiling rom trafc
these alternative
• Colored concrete
bind the aggregate,
materials used to
away, and there is less
tures are not directly
makes the pavement
pavements are used
thus albedo is mainly
construct them.
heat at the surace
related to surace
darker and the sur
or low-trafc areas,
to absorb into the
temperatures and
ace wears away.
such as sidewalks,
pavement.
many complicating
• Urban geometry,
trails, and parking
determined by ag gregate color. • Colored asphalt or
concrete involve pig
• Urban geometry can
inuence the eect high-albedo pave ments have.
actors are involved. – Reected heat can be
particularly urban canyons, inuences
lots. • May be most eec
ments or seals that
absorbed by the sides
the impact high-
tive when paving
are colored and may
o surrounding build
albedo pavements
large, exposed areas,
be more reective
ings warming the in
have on the urban
such as parking lots.
than the conven
terior o the building
climate.
tional equivalent.
and contributing to
These can be applied
the nighttime urban
when new or during
heat island eect,
maintenance.
due to the additional heat that needs to be released rom urban inrastructure.
1 7
Issues and
1 8
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) NEW CONSTRUCTION (continued) Pavement Type
Description o
Properties to Consider
Pavement Temperature
Technology
Urban Climate Impacts
Impacts
Issues and
Target Use
Considerations
Permeable Pavement Options Nonvegetated permeable pavements
• Porous asphalt has
more voids than con ventional asphalt to
+ When wet, lowers
+ When moist, can
• Cooling mecha
• Structurally, avail
ing through
pavement tempera
contribute to lower
nism depends on
able or any use.
evaporation.
ture through evapora
air temperatures day
available moisture.
Rubberized asphalt
tive cooling.
and night, through
Supplemental water
and open-graded
evaporative cooling,
ing may keep them
riction course
cooler.35
asphalt are used on
allow water to drain
• Solar reectance o
through the surace
these materials de
into the base.
pends on individual
at the surace, but
although air tempera
materials (e.g., gravel
subsurace generally
tures are not directly
or crumb rubber, in
may be white and
will be same tempera
related to surace
aid in insulating the
and pervious con
volves mixing shred
very reective). In
ture as nonpermeable
temperatures and
subsurace rom heat
crete actively being
ded rubber into
general, permeable
equivalent.
many complicating
absorption.
asphalt. This material
pavements may be
actors are involved.
• More research
is generally used to
less reective than
reduce noise.
their nonpermeable equivalent due to
asphalts or opengrade course riction
• Rubberized asphalt,
R e d U c I N G U R B A N H e A t I s l A N d s – d R A F t
• Provides cool
• Other porous
suraces can also be
– When dry, may be hot
roads and highways
considered. • Technologies oten
needed to deter
applied to lower
contribute to higher
mine permeable
trafc areas, such as
daytime surace
pavement impacts
parking lots, alleys,
the increased surace
temperatures, but
on pavement and air
area.33
may not aect or may
temperatures.
• Increased convec
– When dry, can
• Void structure may
and trails. • May be best in cli
even reduce night
mates with adequate
used or reducing
tion may help cool
time air temperatures,
moisture during the
noise. 32
the pavement due
although air tempera
summer.
to increased surace
tures are not directly
area. 34
related to surace temperatures and many complicating actors are involved.
c O O l P A V e M e N t s – d R A F t
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) NEW CONSTRUCTION (continued) Pavement Type
Description o
Properties to Consider
Technology
Pavement Temperature
Urban Climate Impacts
Impacts
Issues and
Target Use
Considerations
Permeable Pavement Options (continued) Nonvegetated
• Pervious concrete
permeable pavements
has more voids than
(continued)
conventional con
(see prior page)
(see prior page)
(see prior page)
(see prior page)
(see prior page)
• Provides cooling
+ Lowers pavement
+ In most conditions
• Cooling mecha
• Low-trafc areas,
crete to allow water to drain through the surace into the base. • Brick or block pavers
are generally made rom clay or concrete blocks lled with rocks, gravel, or soil. Vegetated permeable
• Plastic, metal, or
pavements:
concrete lattices
• Grass pavers
provide support and
• Concrete
allow grass or other
grid pavers
through evapotrans
temperatures
will contribute to
nism depends on
piration.
through evapotrans
lower air tempera
available moisture.
piration, particularly
tures day and night,
Supplemental mois
through evapo
ture, or example
mates with adequate
transpiration and
watering pavements,
moisture during the
natural properties o
may keep them
summer.
other pavement
vegetation. Mois
cooler.36
options due to the
ture availability will
natural properties o
greatly increase its
needed to determine
vegetation.
eectiveness.
temperature impacts
• Sustainability o
vegetation to grow
vegetation may vary
when moist.
in the interstices.
with local conditions.
+ When dry may still be cooler than
• More research
rom vegetated pavements under 1 9
a wide range o conditions.
such as alleys, park ing lots, and trails. • May be best in cli
2 0
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) MAINTENANCE/REHABILITATION Pavement Type
Description o
Properties to Consider
Technology
Pavement Temperature
Urban Climate Impacts
Impacts
Issues and
Target Use
Considerations
Reective Pavement Options Chip seals made with
high-albedo aggregate
• Chip seals describe
• Solar reectance o
• Solar reectance
• Chip seals are most
chip seals will corre
ace and subsurace
lower air tempera
decreases over time,
oten used to resur
resurace low-
late with the albedo
temperature because
tures day and night,
as soiling rom trafc
ace low-volume
volume asphalt
o the aggregate
more o the sun’s
although air tempera
makes chip seals
asphalt roads,
roads and some
used. In San Jose, CA,
energy is reected
tures are not directly
darker.
although highway
times or highway
researchers identi
away, and there is less
related to surace
• Urban geometry, in
suraces.
ed albedo o 20%
heat at the surace
temperatures and
particular urban
or new chip seals,
to absorb into the
many complicating
canyons, inuences
which then decline
pavement.
actors are involved.
the impact high-
tive when paving
– Reected heat can be
albedo pavements
large, exposed areas,
absorbed by the sides
have on the urban
such as parking lots.
inuence the eect
o surrounding build
climate.
high-albedo pave
ings warming the in
ments have
terior o the building
with age. 37 • Urban geometry can R e d U c I N G U R B A N H e A t I s l A N d s – d R A F t
+ Lowers pavement sur + Can contribute to
aggregate used to
and contributing to the urban heat island eect.
applications also exist. • May be most eec
c O O l P A V e M e N t s – d R A F t
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) MAINTENANCE/REHABILITATION (continued) Pavement Type
Description o
Properties to Consider
Technology
Pavement Temperature
Urban Climate Impacts
Impacts
Target Use
Considerations
Reective Pavement Options (continued) Whitetopping
• Whitetopping is a
• The solar reectance
+ Lowers pavement sur
thick layer (thick
o whitetopping
ace and subsurace
lower air tempera
decreases over time,
ultra-thin whitetop
ness greater than
material can be as
temperature because
tures day and night,
as soiling rom trafc
ping are generally
high as concrete.
more o the sun’s
although air tempera
makes whitetopped
used to resurace
energy is reected
tures are not directly
suraces darker.
road segments,
4 inches or 10 cm) o concrete applied
• Urban geometry
+ Can contribute to
• Solar reectance
over existing asphalt
can inuence the
away, and there is less
related to surace
• Urban geometry, in
when resuracing
eect o high-albedo
heat at the surace
temperatures and
particular urban
or can be applied to
pavements.
to absorb into the
many complicating
canyons, inuences
actors are involved.
new asphalt. It oten
pavement.
• Whitetopping and
intersections, and parking lots. • May be most eec
the impact high-
tive when paving
– Reected heat can be
albedo pavements
large, exposed areas,
added strength.
absorbed by the sides
have on the urban
such as parking lots.
• Ultra-thin whitetop
o surrounding build
climate.
ping is generally 2–4
ings, warming the in
inches (5–10 cm)
terior o the building
thick and similar to
and contributing to
whitetopping.
the urban heat island
contains bers or
eect.
2 1
Issues and
2 2
Table 2: Properties that Inuence Pavement Temperatures—Impacts and Applications (continued) MAINTENANCE/REHABILITATION (continued) Pavement Type
Description o
Properties to Consider
Technology
Pavement Tempera
Urban Climate Impacts
ture Impacts
Issues and Consider
Target Use
ations
Reective Pavement Options (continued) Microsuracing
with highalbedo materials
•Athinsealing
+ Lowers pavement
+ Can contribute to lower
•Solarreectance
•Usedtoextendpavement
microsuracing will cor-
surace and sub-
air temperatures day and
may decrease over
lie and on worn pave-
maintenance.
relate with the albedo
surace tempera
night, although air tem
time, i soiling rom
ments that need improved
•Light-colored
o the materials used.
ture because more
peratures are not directly
trafc makes high-
riction, such as low- to
o the sun’s energy
related to surace tempera
albedo microsurac
medium-volume roads,
ing materials darker.
airport runways, and park
materials can be
R e d U c I N G U R B A N H e A t I s l A N d s – d R A F t
•Solarreectanceof
layer used or road
•Researchersrecently
used to increase
measured solar reec
is reected away,
tures and many complicat
the solar reec
tances o microsurac
and there is less
ing actors are involved.
tance o asphalt.
ing applications over
heat at the surace
35%.38
to absorb into the
absorbed by the sides o
canyons, inuences
pavement.
surrounding buildings,
the impact high-
warming the interior o the
albedo pavements
building and contributing
have on the urban
to the urban heat island
climate.
– Reected heat can be
eect.
•Urbangeometry,
particularly urban
ing areas.
3 Benets and Costs Currently, ew studies provide detailed data on the benets and costs o cool pavements. This section aims to provide a general discussion as a starting point or decision-makers to consider and gives examples where available. Again, decisionmakers will also consider location-specic actors such as unctionality o pavements in the local climate, political acceptance, and experience with the technology. Re sources and examples providing the latest inormation are listed in Sections 4 and 5.
3.1 Benets Installing cool pavements can be part o an overall strategy to reduce air tempera tures, which can result in a wide range o benets. The inormation below highlights existing research in this area. Reduced Energy Use
As noted earlier, researchers predicted that i pavement refectance throughout a city were increased rom 10 to 35 percent, the air temperature could potentially be re duced by 1°F (0.6°C), which would result in signicant benets in terms o lower energy use and reduced ozone levels. For example, an earlier, separate study esti mated over $90 million/year in savings rom temperature reductions attributed to increased pavement albedo in the Los An geles area.39 Similarly, when permeable pavements evaporate water and contribute to lower air temperatures, they also provide other energy benets.40 Permeable pavements can allow stormwater to inltrate into the ground, which decreases stormwater runo. With reduced runo, communities may realize energy savings associated with pumping stormwater and maintaining con veyance structures. These cost savings may
cOOl PAVeMeNts – dRAFt
Measuring Energy Savings rom Cool Roos versus Cool Pavements Measuring the energy impacts rom a cool roo is relatively easy compared with quantiying those rom pave ment installations. With a roo, one can measure energy demand beore and ater the installation, and in a controlled experiment, the change in demand can be associated with the roong technology. In contrast, pave ments aect building energy demand through infuencing air temperature, which is a more complex relation ship to isolate and measure. be signicant in areas where there are old, combined sewers (where stormwater drains into the sanitary sewer system). Air Quality and Greenhouse Gas Emissions
Depending on the electric power uel mix, decreased energy demand associated with cool pavements will result in lower as sociated air pollution and greenhouse gas emissions. Cooler air temperatures also slow the rate o ground-level ozone or mation and reduce evaporative emissions rom vehicles. A 2007 paper estimated that increasing pavement albedo in cit ies worldwide, rom an average o 35 to 39 percent, could achieve reductions in global carbon dioxide (CO2) emissions worth about $400 billion.41 Water Quality and Stormwater Runo
Pavements with lower surace temperatures—whether due to high solar refec tance, permeability, or other actors—can help lower the temperature o stormwater runo, thus ameliorating thermal shock to
23
aquatic lie in the waterways into which stormwater drains.42 Laboratory tests with permeable pavers have shown reductions in runo temperatures o about 3–7ºF (2–4ºC) in comparison with conventional asphalt paving.43 Permeable pavements allow water to soak into the pavement and soil, thereby reducing stormwater runo, recharging soil moisture, and improving water qual ity by ltering out dust, dirt, and pollut ants.44,45 Outdoor testing and laboratory measurements have ound that permeable pavements can reduce runo by up to 90 percent.46 Reducing runo decreases scouring o streams, and, in areas with combined sewers, this fow reduction can help minimize combined sewer overfows that discharge sewage and stormwater into receiving waters. The amount o water that these pavements collect varies based on the type o aggregate used and the po rosity o the pavements, as well as on the absorptive ability o the materials support ing the pavement.
Figure 9: Slag Cement Airport Expansion
n o i t a i c o s s A t n e m e C g a l S
The Detroit Metro Airport used 720,000 square eet (67,000 m2) o slag cement in an airport terminal expansion project. In this region, the local aggregate is susceptible to alkali-silica reaction, whereas slag resists that orm o corrosion better than plain cement and is easier to place in hot weather. This approach increased the lie expectancy o the paved suraces, as well as allowed or the use o a high-albedo product. 48
take pavement color into account when planning lighting.49 •
tive or permeable pavements where people congregate or children play can provide localized comort benets through lower surace and near-surace air temperatures.50
Increased Pavement Lie and Waste Reduction
Reducing pavement surace temperatures can increase the useul lie o pavements and reduce waste. Some simulations o asphalt pavements showed that pavements that were 20°F (11°C) cooler lasted 10 times longer than the hotter pavements, and pavements that were 40°F (22°C) cool er lasted 100 times longer beore showing permanent damage.47
•
Cool pavements may provide additional benets, such as: Nighttime illumination. Refective
pavements can enhance visibility at night, potentially reducing lighting requirements and saving money and energy. European road designers oten 24
Noise reduction. The open pores o
permeable pavements, such as an opengraded course layer on highways, can reduce tire noise by two to eight deci bels and keep noise levels below 75 decibels.51,52 Noise reduction may de cline over time, however, and some o these pavements may not be as strong and durable as conventional suraces. Researchers at the National Center o Excellence at Arizona State University are studying these issues.53
Quality o Lie Benefts
•
Comort improvements. Using refec
•
Saety. Permeable roadway pavements
can enhance saety because better wa ter drainage reduces water spray rom moving vehicles, increases traction, and may improve visibility by draining wa ter that increases glare.54 RedUcING URBAN HeAt IslANds – dRAFt
3.2 Costs Cool pavement costs will depend on many actors including the ollowing: •
The region
•
Local climate
•
Contractor
•
Time o year
•
Accessibility o the site
•
Underlying soils
•
Project size
•
Expected trac
•
The desired lie o the pavement.
Most cost inormation is project specic, and ew resources exist that provide general cost inormation. For permeable pavement, however, the Federal Highway Administration (FHWA) has noted that
porous asphalt costs approximately 10 to 15 percent more than regular asphalt, and porous concrete is about 25 percent more expensive than conventional concrete. 55 These comparisons pertain to the surace layer only. Table 3 (below) summarizes a range o costs or conventional and cool pave ments, based on available sources. The data should be read with caution, as many project-specic actors—as highlighted above—will infuence costs. These costs are estimates or initial construction or perorming maintenance, and do not refect lie-cycle costs. Decision-makers generally contact local paving associations and contractors to obtain more detailed, location-specic inormation on the costs and viability o cool pavements in their particular area.
Table 3: Comparative Costs o Various Pavements56 Approximate Basic Pavement Types
Example Cool Approaches
Installed Cost,
Estimated Service
$/square oot*
Lie, Years
New Construction Asphalt (conventional)
Hot mix asphalt with light aggregate,
$0.10–$1.50
7–20
i locally available Concrete (conventional)
Portland cement, plain-jointed
$0.30–$4.50
15–35
Nonvegetated permeable pave-
Porous asphalt
$2.00–$2.50
7–10
ment
Pervious concrete
$5.00–$6.25
15–20
Paving blocks
$5.00–$10.00
> 20
Grass/gravel pavers
$1.50–$5.75
> 10
$0.10–$0.15
2–8
Microsuracing
$0.35–$0.65
7–10
Ultra-thin whitetopping
$1.50–$6.50
10–15
Vegetated permeable pavement
Maintenance Surace applications
Chip seals with light aggregate, i locally available
* Some technologies, such as permeable options, may reduce the need or other inrastructure, such as stormwater drains, thus lowering a project’s overall expenses. Those savings, however, are not reected in this table. (1 square oot = 0.09 m2)
cOOl PAVeMeNts – dRAFt
25
3.3 Benet-Cost Considerations Lie-cycle cost assessments can help in evaluating whether long-term benets can outweigh higher up-ront costs. The National Institute o Standards and Tech nology (NIST) has developed Building or Environmental and Economic Sustainabil ity (BEES), a sotware tool that uses the ISO 14040 series o standards to estimate lie-cycle costs rom the production and use o asphalt, Portland cement, fy ash cement, and other paving materials. 57 Al though not directly related to urban heat island mitigation, this tool can help quan tiy some o the impacts rom a variety o pavement choices. Further, although permeable pavement costs may be higher than conventional, impermeable technologies, these costs are oten oset by savings rom reduced re quirements or grading, treatment ponds, or other drainage eatures, such as inlets and stormwater pipes.58 For a community, the cumulative reductions in stormwater fows rom sites can provide signicant savings in the municipal inrastructure. I the community has combined sewers, there could also be environmental, social, and cost benets rom reducing combined sewer overfows, as well as potentially avoiding part o the increased inrastruc ture costs associated with combined sewer operation. In general, until more data on cool pave ment benets and costs exist, communities may need to think broadly to determine i a cool pavement application is appropriate. Sustainability initiatives, in some areas, are motivating communities to try cooler alter natives, as discussed in Section 4.
26
4 Cool Pavement Initiatives The growing interest in lowering urban temperatures and designing more sustain able communities has helped spur activ ity in the cool pavement arena. Most o the eort has ocused on research, due to inormation gaps and the lack o specic data quantiying cool pavement benets. More inormation on resources and exam ples are provided at the end o this sec tion and in Section 5. Highlights o some cool pavement eorts are below: •
Arizona State University’s National Center o Excellence (NCE) SMART Innovations or Urban Climate and Energy. 59 This group is studying es
tablished and emerging designs that optimize albedo, emissivity, thermal conductivity, heat storage capacity, and density in laboratory and eld sites. NCE is developing models, particularly or the Phoenix area but also beyond, to help decision-makers predict the eects o material properties, shading, and energy use on urban temperatures. •
The National Academies o Science’s Transportation Research Board (TRB) Subcommittee on Paving Ma terials and the Urban Climate. TRB
established this Subcommittee in Janu ary 2008 to help advance the science o using pavements or heat island mitiga tion and addressing other urban climate concerns. •
Trade association eorts. Represen
tatives rom the asphalt and concrete trade associations are participating in cool pavement eorts, such as the TRB Subcommittee on Paving Materials and the Urban Climate, as well supporting research and training related to cool pavement. For example, the National
RedUcING URBAN HeAt IslANds – dRAFt
Asphalt Pavement Association has been investigating high-albedo asphalt pave ments, the National Ready Mixed Con crete Association is leading seminars on pervious concrete, and the Interlocking Concrete Pavement Institute (ICPI) is providing proessional seminars on per meable pavements in cooperation with the Low Impact Development Center and North Carolina State University. 60 These research eorts are expanding op portunities or identiying, applying, and studying cool pavement technologies. Sustainability or green building initiatives are helping to encourage cool pavement installations. •
Evanston, Illinois, includes permeable
pavements in its assessment o green buildings.61 •
Chicago’s Green Alley program aims
Growing Concern about Synthetic Tur Many communities have begun to examine the health impacts rom synthetic tur suraces, which include the eects rom high temperatures. One researcher in New York ound that articial sports elds could be up to 60°F (16°C) hotter than grass, potentially causing skin injuries to athletes as well as contributing to the heat island eect. These data, though not directly related to pavements, can help advance our understanding o how dierent materials interact with the urban climate.63
Figure 11: Grass Paving
to use green construction techniques to repave over 1,900 miles o alleys, and oers a handbook or installing per meable pavements or heat reduction, stormwater management, and other benets.62 •
Environmental rating programs such
as Leadership in Energy and Environ mental Design (LEED), Green Globes, and EarthCrat award points to designs that incorporate certain permeable pavements or pavements o a certain solar refectance index. They also give points or using local and recycled ma terials, such as slag, and reducing the pavement used on a site. Table 4 on page 28 summarizes other cool pavement initiatives. Reer to the “Heat Island Reduction Activities” chapter o this compendium or urther examples.
cOOl PAVeMeNts – dRAFt
C R A H , k c o c h c t i H d i v a D
This 300,000-square-oot (28,000 m2) parking lot outside a stadium in Houston uses plastic grid pavers that allow grass to grow in the open spaces.
27
Alternative Paving under the Cool Houston Plan While most communities have no, or limited, cool pavement experience, Houston’s heat island initiative recommends alternative pavements as part o the city’s overall approach to improving air quality and public health. The plan’s three-tiered strategy includes: •
•
•
Targeting alternative paving options or specic types o paved suraces, such as highways or parking lots, or expanding residential or commercial roadways. This requires coordination with the Texas Department o Transportation and the Texas Commission on Environmental Quality. Educating local and state decision-makers about public health, environmental management, and public works maintenance benets o alternative pavements. Combining and embedding alternative paving incentives into larger programs and regulations, such as meeting Clean Air or Clean Water Act standards, with the support o the Greater Houston Builders Association and the Texas Aggregates and Concrete Association.
Table 4: Examples o Cool Pavement Initiatives Type o Initiative Research
Description Industry
Links to Examples —Since 1928, the National Ready Mixed Concrete Association’s research laboratory has helped evaluate materials and set technical standards. Recent projects include developing permeability tests and assessing concrete with high yash content.
National
—Th e Heat Island Group at Lawrence
laboratory
Berkeley National Laboratory (LBNL) provides research and inormation about cool paving and other heat island mitigation measures. The Cool Pavements section describes the benets o this technology, and published reports are included under Recent Publications.
University-
—Arizona State University’s National Center
supported
o Excellence collaborates with industry and government to research and develop
and similar
technologies to reduce urban heat islands, especially in desert climates.
consortia
—The Houston Advanced Research Center (HARC) brings together universities, local governments, and other groups interested in improving air quality and reducing heat islands. It has examined how cool paving could be implemented in the Houston area to reduce urban heat island eects. and —North Carolina State University has an active permeable pavement research program, as well as a specialized collaborative eort with ICPI and the Low Impact Development Center on permeable interlocking concrete pavements.
28
RedUcING URBAN HeAt IslANds – dRAFt
Table 4: Examples o Cool Pavement Initiatives (cont.) Type o Initiative
Description
Links to Examples
Voluntary
Demonstration
—
eorts
programs
Poulsbo, Washington, used a $263,000 grant rom the Washington Department o Ecology to pave 2,000 eet o sidewalk with pervious pavement, making it one o the largest pervious surace projects in the state. —Th e nonprot Heier Interna tional used pervious pavement and other sustainable techniques or its new head quarters in Arkansas.
Outreach &
< www.epa.gov/heatisland/>—EPA’s Heat Island Reduction Initiative provides inor
education
mation on the temperature, energy, and air quality impacts rom cool pavements and other heat island mitigation strategies. —EPA’s Ofce o Water highlights design options, including permeable pavements that reduce stormwater runo and water pollution. —The Green Highways Partnership, supported by a number o groups including EPA and the U.S. Department o Transportation is a public-private partnership dedicated to transorming the relationship between the environment and transportation inrastructure. The partnership’s Web site includes a number o cool pave ment resources, especially with respect to permeable pavements. —Th e University o Connecticut runs Nonpoint Education or Municipal Ofcials (NEMO), which helps educate local governments about land use and environmental quality.
Tools www.brl.nist.gov/oae/sotware/bees/>—The < National Institute o Standards and Technology (NIST) has developed a sotware tool, Building or Environmental and Economic Stability (BEES). The tool enables communities to conduct lie cycle cost assessments or various types o building initiatives, including pavement projects.
Policy
Municipal
—Th e Cool Hous
eorts
regulations that
ton! Plan promotes cool paving as well as other techniques to reduce the region’s
support cool
heat island.
pavements
— Toronto’s “Design Guidelines or ‘Greening’ Surace Parking Lots” encourage reective and permeable pavements to reduce sur ace temperatures.
Although cool pavements are still in their inancy compared with the other heat island mitigation strategies—trees and veg etation, green roos, and cool roos—inter est and momentum are growing. Research eorts these past ew years have greatly increased, particularly in the area o per meable pavements. As local and state trans portation and environmental agencies work together to address energy, sustainability, cOOl PAVeMeNts – dRAFt
heat-health, and other concerns, communi ties can expect to see more cool pavement installations. Activity in the private sector has also been encouraging, as architects, developers, and others are taking leader ship roles in advancing sustainable tech nologies. This chapter, which currently provides a starting point or communities and decision-makers, will evolve as more inormation becomes available. 29
5 Resources The organizations below may provide additional inormation on alternative, or cool, pavement technologies. Program/Organization
Role
Web Address
The Federal Highway
The Ofce o Pavement Technology conducts research
Administration’s (FHWA)
and training related to asphalt and concrete pavements.
pavement/hq/welcome.
Ofce o Pavement
cm>
Technology FHWA’s Ofce o Planning,
This ofce’s Web site provides inormation regarding
Environment, and Realty
transportation planning and the environment.
index.htm>
American Association
AASHTO created the Center or Environmental Excellence
o State Highway and
in cooperation with the Federal Highway Administration
transportation.org/>
Transportation Ofcials
to oer technical assistance about environmental
Center or Environmental
regulations and ways to meet them.
Excellence (AASHTO) Association o Metropolitan
AMPO supports local MPOs through training,
Planning Organizations
conerences, and assistance with policy development.
(AMPO) The American Concrete
ACPA promotes concrete pavement by working with
Pavement Association (ACPA)
industry and government.
The Asphalt Pavement
A consortium o the National Asphalt Paving Association
Alliance (APA)
(NAPA), the Asphalt Institute (AI), and state paving
com>
associations, APA promotes hot mix asphalt through research, development, and outreach. Individual state asphalt associations are a good source or local paving considerations. Interlocking Concrete
ICPI has a document that compares permeable pavement
Pavement Institute (ICPI)
technologies and helps readers nd certied installers.
National Center or Asphalt
NCAT provides up-to-date strategies or designing and
Technology (NCAT)
constructing asphalt pavements.
National Ready Mixed
Since 1928, the National Ready Mixed Concrete
Concrete Association
Association’s research laboratory has helped evaluate
materials and set technical standards. Recent projects include developing permeability tests and assessing concrete with high y-ash content. Portland Cement Association
PCA represents cement companies in the United States
(PCA)
and Canada and conducts research, development, and
outreach.
30
RedUcING URBAN HeAt IslANds – dRAFt
Endnotes 1
Statistics are rom urban abric analyses conducted by Lawrence Berkeley National Laboratory. Rose, L.S., H. Akbari, and H. Taha. 2003. Characterizing the Fabric o the Urban Environment: A Case Study o Greater Houston, Texas. Texas. Paper LBNL-51448. Lawrence Berkeley National Labora tory, Berkeley, CA. Akbari, H. and L.S. Rose. 2001. Characterizing the Fabric o the Urban Environment: A Case Study o Metropolitan Chicago, Illinois. Paper LBNL-49275. Lawrence Berkeley National Labora tory, Berkeley Berkeley,, CA. Akbari, H. and L.S. Rose. 2001. Characterizing the Fabric o the Urban Envi ronment: A Case Study o Salt Lake City, Utah. Paper LBNL-47851. Lawrence Berkeley Berkeley National Laboratory, Berkeley, CA. Akbari, H., L.S. Rose, and H. Taha. 1999. Characterizing the Fabric o the Urban Environment: A Case Study o Sacramento, Caliornia. Paper LBNL-44688. Lawrence Berkeley National Laboratory, Berkeley, CA.
2
Pomerantz, M., B. Pon, H. Akbari, and S.-C. Chang. 2000. The Eect o Pavements’ Temperatures on Air Temperatures in Large Cities. Paper LBNL-43442. Lawrence Berkeley National Laboratory, Berkeley,, CA. See also Cambridge Systematics. 2005. Cool Pavement Drat Repor t. Prepared or Berkeley U.S. EPA.
3
See, generally, U.S. EPA 2008. Green Parking Lot Resource Guide. EPA 510-B-08-001.
4
Golden, J.S., J. Carlson, K. Kaloush, and P. Phelan. 2006. A Comparative Study o the Thermal and Radiative Impacts o Photovoltaic Canopies on Pave Pavement ment Surace Temperatures. Solar Energy.. 81(7): 872-883. Energy 872-883 . July 2007.
5
Kinouchi, T., T. Yoshinaka, N. Fukae, and M. Kanda. 2004. Development o Cool Pavement with Dark Colored High Albedo Coating. Paper or 5th Conerence or the Urban Environment. Vancouver, Canada. Retrieved November 15, 2007, rom .
6
National Center o Excellence on SMART Innovations at Arizona State University. 2007. What Fac tors Infuence Elevated Pavement Temperatures Most During Day and Night? Case Study 1(1).
7
The Portland Cement Association thoroughly explains concrete cement at < www.cement.org/ < www.cement.org/ tech/cct_concrete_prod.asp>, tech/cct_concrete_pr od.asp>, a nd state and ederal government sites, among others, dene as phalt. Two Two useul ones are < www www.virginiadot.org/business/re .virginiadot.org/business/resources/bu-mat-Chapt1AP sources/bu-mat-Chapt1AP.pd> .pd> and < www.thrc.gov/hnr20/recycle/waste/app.htm>.
8
Levinson, R. and H. Akbari. 2001. Eects o Composition and Exposure on the Solar Refec tance o Portland Cement Concrete. Paper LBNL-48334. Lawrence Berkeley National Laboratory, Berkeley, CA.
9
National Center o Excellence on SMART Innovations at Arizona State University. 2007. What Factors Infuence Elevated Pavement Temperatures Temperatures Most During Day and Night? Case Study 1(1).
10
Levinson, R., H. Akbari, S. Konopacki, Konopacki, and S. Bretz. 2002. Inclusion o Cool Roos in Nonresi dential Title 24 Prescriptive Requirements. Paper LBNL-50451. Lawrence Berkeley National Laboratory, Berkeley, CA.
11
See: Haselbach, L. 2008. Pervious Concrete and Mitigation o the Urban Heat Island Eect. Un der review or the 2009 Transportation Research Board Annual Meeting. Kevern, J., V.R. Schaeer, and K. Wong. 2008. Temperature Behavior o a Pervious Concrete System. Under review or the 2009 200 9 Transportation Research Board Annual Meeting.
cOOl PAVeMeNts – dRAFt
31
12
For a general overview o permeable pavements, see Ferguson, B. 2005. Porous Pavements.
13
See, generally: Haselbach, L. 2008. Pervious Concrete and Mitigation o the Urban Heat Island Eect. Un der review or the 2009 Transportation Research Board Annual Meeting. Kevern, J., V.R. Schaeer, and K. Wong. 2008. Temperature Behavior o a Pervious Concrete System. Under review or the 2009 Transportation Research Board Annual Meeting.
14
There are a number o resources available on Japan’s eorts with water retentive pave ments, although there is no centralized source that compiles these initiatives. For examples o the research and published summaries available, see the ollowing (all Web sites accessed September 17, 2008): Karasawa, A., K. Toriiminami, N. Ezumi, K. Kamaya. 2006. Evaluation O Perormance O Water-Retentive Concrete Block Pavements. 8th International Conerence on Concrete Block Paving, November 6-8, 2006, San Francisco, Caliornia. Ishizuka, R., E. Fujiwara, H. Akagawa. 2006. Study On Applicability O Water-Feed-Type Wet Block Pavement To Roadways. 8th International Conerence on Concrete Block Paving, November 6-8, 2006, San Francisco, Caliornia. Yamamoto, Y. 2006. Measures to Mitigate Urban Heat Islands. Quarterly Review No. 18. January 2006. Available online at < www.nistep.go.jp/achiev/tx/eng/stc/stt018e/qr18pd/ STTqr1806.pd>. Yoshioka, M., H. Tosaka, K. Nakagawa 2007. Experimental and Numerical Studies o the Eects o Water Sprinkling on Urban Pavement on Heat Island Mitigation. American Geo physical Union, Fall Meeting 2007, abstract #H43D-1607. Yamagata H., M. Nasu, M. Yoshizawa, A. Miyamoto, and M. Minamiyama. 2008. Heat island mitigation using water retentive pavement sprinkled with reclaimed wastewater. Water science and technology. 57(5): 763-771. Abstract available online at < http://cat.inist.r/ ?aModele=acheN&cpsidt=20266221>.
15
Christen, A. and R. Vogt. 2004. Energy and radiation balance o a Central European city. Interna tional Journal o Climatology. 24(ii):1395-1421.
16
Golden, J.S. and K. Kaloush. 2006. Meso-Scale and Micro-Scale Evaluations o Surace Pavement Impacts to the Urban Heat Island Eects. The International Journal o Pavement Engineering. 7(1): 37-52. March 2006.
17
Pomerantz, M., B. Pon, H. Akbari, and S.-C. Chang. 2000. The Eect o Pavements’ Temperatures on Air Temperatures in Large Cities. Paper LBNL-43442. Lawrence Berkeley National Laboratory, Berkeley, CA.
18
Taha, H. 1997. Modeling the impacts o large-scale albedo changes on ozone air quality in the South Coast Air Basin. Atmospheric Environment. 31(11): 1667-1676 . Taha, H. 1996. Modeling the Impacts o Increased Urban Vegetation on the Ozone Air Quality in the South Coast Air Basin. Atmospheric Environment. 30(20): 3423-3430.
19
20
32
Roseneld, A.H., J.J. Romm, H. Akbari, and M. Pomerantz. 1998. Cool Communities: Strategies or Heat Islands Mitigation and Smog Reduction. Energy and Buildings. 28:51-62. Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strategies or Design and Con struction o High-Refectance Asphalt Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
RedUcING URBAN HeAt IslANds – dRAFt
21
22
23
Statistics are rom urban abric analyses conducted by Lawrence Berkeley National Laboratory. Rose, L.S., H. Akbari, and H. Taha. 2003. Characterizing the Fabric o the Urban Environment: A Case Study o Greater Houston, Texas. Paper LBNL-51448. Lawrence Berkeley National Labora tory, Berkeley, CA. Akbari, H. and L.S. Rose. 2001. Characterizing the Fabric o the Urban Environment: A Case Study o Metropolitan Chicago, Illinois. Paper LBNL-49275. Lawrence Berkeley National Labora tory, Berkeley, CA. Akbari, H. and L.S. Rose. 2001. Characterizing the Fabric o the Urban Envi ronment: A Case Study o Salt Lake City, Utah. Paper LBNL-47851. Lawrence Berkeley National Laboratory, Berkeley, CA. Akbari, H., L.S. Rose, and H. Taha. 1999. Characterizing the Fabric o the Urban Environment: A Case Study o Sacramento, Caliornia. Paper LBNL-44688. Lawrence Berkeley National Laboratory, Berkeley, CA. See, e.g., Mallick, R.B., P.S. Kandhal, L.A. Cooley, Jr., and P.E. Watson. 2000. Design, Construc tion, and Perormance o New-generation Open-graded Friction Courses. Paper prepared or annual meeting o Association o Asphalt Paving Technologists, Reno, NV, March 13-15, 2000. Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strategies or Design and Con struction o High-Refectance Asphalt Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
24
More inormation on fy ash is available through EPA’s Coal Combustion Products Partnership, < www.epa.gov/rcc/c2p2/index.htm>.
25
Boriboonsomsin, K. and F. Reza. 2007. Mix Design and Benet Evaluation o High Solar Refec tance Concrete or Pavements. Paper or 86 th Annual Meeting o the Transportation Research Board. Washington, D.C.
26
Oce o the Governor. 2006. Statement by Gov. Schwarzenegger on U.S. EPA Award or Cali ornia’s Leadership in the Construction Use o Waste Products. Retrieved July 15, 2008, rom
27
Pomerantz, M., B. Pon, H. Akbari, and S.-C. Chang. 2000. The Eect o Pavements’ Temperatures On Air Temperatures in Large Cities. Paper LBNL-43442 . Lawrence Berkeley National Labora tory, Berkeley, CA. See also Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strate gies or Design and Construction o High-Refectance Asphalt Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
28
Aseda, T., V.T. Ca, and A. Wake. 1993. Heat Storage o Pavement and its Eect on the Lower Atmosphere. Atmospheric Environment. 30(3): 413–427. 1996.
29
Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strategies or Design and Con struction o High-Refectance Asphalt Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
30
Levinson, R. and H. Akbari. 2001. Eects o Composition and Exposure on the Solar Refec tance o Portland Cement Concrete. Paper LBNL-48334. Lawrence Berkeley National Laboratory, Berkeley, CA.
31
Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strategies or Design and Con struction o High-Refectance Asphalt Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
32
National Center o Excellence on SMART Innovations at Arizona State University. 2007. Alternative Paving—Recycling Crumb Rubber. Case Study, 1(3).
33
Haselbach, L. 2008. Pervious Concrete and Mitigation o the Urban Heat Island Eect. Under review or the 2009 Transportation Research Board Annual Meeting.
cOOl PAVeMeNts – dRAFt
33
34
Haselbach, L. 2008. Pervious Concrete and Mitigation o the Urban Heat Island Eect. Under review or the 2009 Transportation Research Board Annual Meeting.
35
Yamagata H., M. Nasu, M. Yoshizawa, A. Miyamoto, and M. Minamiyama. 2008. Heat island miti gation using water retentive pavement sprinkled with reclaimed wastewater. Water science and technology. 57(5): 763-771. Abstract available online at < http://cat.inist.r/?aModele=acheN&c psidt=20266221>.
36
Yamagata H., M. Nasu, M. Yoshizawa, A. Miyamoto, and M. Minamiyama. 2008. Heat island miti gation using water retentive pavement sprinkled with reclaimed wastewater. Water science and technology. 57(5): 763-771. Abstract available online at < http://cat.inist.r/?aModele=acheN&c psidt=20266221>.
37
38
Pomerantz, M., H. Akbari, S.-C. Chang, R. Levinson and B. Pon. 2003. E xamples o Cooler Refec tive Streets or Urban Heat-Island Mitigation: Portland Cement Concrete and Chip Seals. Paper LBNL-49283. Lawrence Berkeley National Laboratory, Berkeley, CA. Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strategies or Design and Con struction o High-Refectance Asphalt Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
39
Roseneld, A.H., J.J. Romm, H. Akbari, and M. Pomerantz. 1998. “Cool Communities: Strategies or Heat Islands Mitigation and Smog Reduction,” Energy and Buildings, 28, pp. 51-62.
40
Pomerantz, M., B. Pon, H. Akbari, and S.-C. Chang. 2000. The Eect o Pavements’ Temperatures on Air Temperatures in Large Cities. Paper LBNL-43442. Lawrence Berkeley National Laboratory, Berkeley, CA.
41
Akbari, H., and S. Menon. 2007. Global Cooling: Eect o Urban Albedo on Global Temperature. Paper or the Proceedings o the International Seminar on Planetary Emergencies. Erice, Sicily.
42
43
U.S. EPA. 2003. Beating the Heat: Mitigating Thermal Impacts. Nonpoint Source News-Notes. 72:23-26. James, W. 2002. Green Roads: Research into Permeable Pavers. Stormwater. Retrieved May 8, 2008 rom < www.stormcon.com/sw_0203_green.html>.
44
U.S. EPA. Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices. EPA 841-F-07-006, December 2007. Retrieved April 2, 2008 rom < www.epa.gov/ owow/nps/lid/costs07/>.
45
Booth, D. and J. Leavit. 1999. Field Evaluation o Permeable Pavement Systems or Improved Stormwater Management. Journal o the American Planning Association. 65(3): 314-325.
46
James, W. 2002. Green Roads: Research into Permeable Pavers. Stormwater. Retrieved May 8, 2008 rom < www.stormcon.com/sw_0203_green.html>.
47
Pomerantz, M., H. Akbari, and J. Harvey. 2000. Durability and Visibility Benets o Cooler Re fective Pavements. Paper LBNL-43443. Lawrence Berkeley National Laboratory, Berkeley, CA.
48
Bijen, Jan. 1996. Benets o slag and fy ash. Construction and Building Materials 10.5: 30 9-314. See also the Federal Highway Administration’s summary o slag cement at < www.thrc.gov/ hnr20/recycle/waste/bs3.htm>.
49
U.S. Department o Transportation, Federal Highway Administration. European Road Lighting Technologies. International Technology Exchange Program: September 2001. Retrieved June 16, 2008, rom . See also: Interna tional Commission on Illumination. 2007. Road Transport Lighting or Developing Countries. CIE 180:2007.
34
RedUcING URBAN HeAt IslANds – dRAFt
50
Kinouchi, T., T. Yoshinaka, N. Fukae, and M. Kanda. 2004. Development o Cool Pavement with Dark Colored High Albedo Coating. Paper or 5 th Conerence or the Urban Environment. Vancouver Va ncouver,, Canada. Retrieved November 15, 2007, rom .
51
Glazier, G. and S. Samuels. 1991. Eects o Road Surace Texture on Trac and Vehicle Noise. Transportation Research Record. 1312: 141-144.
52
53
Pipien, G. 1995. Pervious Cement Concrete Wearing Wearing Course Oering Less than 75 dB(A) Noise Level. Revue Revue Generale des Routes et Aerodromes. 735: 33-36. National Center o Excellence on SMART Innovations at Arizona State University. 2007. Alternative Paving—Recycling Crumb Rubber. Case Study, 1(3).
54
U.S. Department o Transportation, Federal Highway Transportation Administration. 2005. Tech nical Advisory: Surace Texture or Asphalt and Concrete Pavements. Retrieved Retrieved September 17, 2008, rom < www.hwa.dot.gov/legsregs/directiv ww.hwa.dot.gov/legsregs/directives/techadvs/t504036.htm>. es/techadvs/t504036.htm>. M ichigan Depart ment o Environmental Quality. Quality. 1992. Porous Asphalt Pavem Pavement. ent. Retrieved 16 Sep 2008 rom < www.deq.state.mi.us/documents/deq-swq-nps-pap.pd>.
55
U.S. Department o Transportation, Federal Highway Administration. Stormwater Best Manage ment Practices in an Ultra-Urban Setting: Selection and Monitoring. Fact Sheet - Porous Pave ments. Retrieved Retrieved April 2, 2008, rom < www.hwa.dot.gov/environment/ultraurb/3s15.htm>.
56
Figures are taken rom multiples sources and express the maximum range o the values: 1) Cambridge Systematics. 2005. Cool Pavement Drat Report. Prepared or U.S. EPA. 2) ASU’s drat o the Phoenix Energy and Climate Guidebook. 3) Center or Watershed Watershed Protection. 2007. Rede velopment Projects. New York York State Stormwater Management Design Manual. Prepared or New York Y ork State Department o Environmental Conservation. Retrieved June 13, 2008, rom < www. < www. dec.ny.gov/docs/water_pd/ dec.ny .gov/docs/water_pd/swdmredev swdmredevelop.pd>. elop.pd>. 4) Bean, E.Z.,W.F. Hunt, D.A. Bidelspach, and J.T.. Smith. 2004. Study on the Surace Inltration Rate o Permeable Pavements. J.T Pavements. Prepared or Interlocking Concrete Pavement Institute. 5) Interlocking Concrete Pavement Institute. 2008. Permeable Interlocking Concrete Pavements: Pavements: A Comparison Guide to Porous Asphalt and Pervi ous Concrete. 6) Pratt, C.J. 2004. Sustainable Drainage: A Review o Published Material on the Perormance o Various SUDS Components. Prepared or The Environment Agency. Agency. Retrieved June 13, 2008, rom < www.ciria.org/suds/pd/suds_lit_re www.ciria.org/suds/pd/suds_lit_review_04.pd>. view_04.pd>. 7) NDS, Inc. Technical Specications or Grass Pavers. Retrieved June 13, 2008, rom < www.ndspro.com/cms/inde < www.ndspro.com/cms/inde x. php/Engineers-and-Architects.html>. php/Engineers-and-Architects.html >. 8) Tran, N., B. Powell, H. Marks, R. West, and A. Kvasnak. 2008. Strategies or Design and Construction o High-Refectance Asphalt Pavements. Pavements. Under review or the 2009 Transportation Research Board Annual Meeting.
57
See the Building or Environmental and Economic Sustainability (BEES) sotware at < www.brl.nist.gov/oae/sotware/bees/>.
58
U.S. EPA. EPA. 2007. Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices. EPA 841-F-07-006. Retrieved April 2, 2008, rom < www.epa.gov/owow/nps/li d/ costs07/documents/reducingstormwatercosts.pd >. >.
59
National Center o Excellence on SMART Innovations at Arizona State University .
cOOl PAVeMeNts – dRAFt
35
