Reducing Urban Heat Islands: Cool Pavements

8/9/2019 Reducing Urban Heat Islands: Cool Pavements

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Reducing Urban Heat IslandsCompendium of Strategies

Cool Pavements

cOOl PAVeMeNts dRAFt 21


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Acknowledgements

Reducing Urban Heat Islands: Compendium of Strategiesdescribes the

causes and impacts o summertime urban heat islands and promotes

strategies or lowering temperatures in U.S. communities. This compendium

was developed by the Climate Protection Partnership Division in the U.S.

Environmental Protection Agencys 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 EPAs Heat Island Reduction Initiative.

Experts who helped shape this chapter include: Bruce Ferguson, Kim Fisher,

Jay Golden, Lisa Hair, Liv Haselbach, David Hitchcock, Kamil Kaloush, Mel

Pomerantz, Nam Tran, and Don Waye.


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Contents

Cool Pavements 1

1. How It Works. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .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

1.4 Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

1.5 Other Factors to Consider. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

1.6 Temperature Eects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

2. Potential Cool Pavement Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

3. Benets and Costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

3.1 Benets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

3.2 Costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

3.3 Benet-Cost Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

4. Cool Pavement Initiatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

5. Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Endnotes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31


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Cool PavementsCool pavements reer to a range oestablished and emerging materials.These pavement technologies tend tostore 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. Communities 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 120150F (4867C).2These

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 heatstormwater 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 communitys land cover, compared

with roo and vegetated suraces. As part o EPAs

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 showsthe 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 suns energy contributing to the

urban heat island eect, accounted or nearly 30 to

45 percent o land cover.

0 5 10 15 20 25 30 35 40 45 50

Chicago

Houston

Sacramento

Salt Lake City

Percent Coverage

Figure 1: Paved Surace Statistics or Four U.S. Cities

* 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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Figure 2: Conventional Pavement Temperatures

NationalCenteroExcellenceonSMARTInnova-

tionsatArizonaStateUniversity

This picture o Phoenix, Arizona, in the summer shows a variety o conventional pavements that reached

temperatures up to 150F (67C).

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 pavementswhich allow

air, water, and water vapor into the voids o a pavement, keeping the material cool

when moistsome 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 understandbetter 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 policy-

makers are directing more attention to the

impact pavements have on local and global

climates. This chapter discusses:

Pavement properties and how theycan be modied to reduce urban heat

islands

Conditions that aect pavement properties

Potential cool pavement technologies Cool pavement benets and costs

Cool pavement initiatives and researcheorts

Resources or urther inormation.Given that cool pavements are an evolv

ing technology and much is still unknownabout 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

RedUcING URBAN HeAt IslANds dRAFt2


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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 propertiessurace solar refectance and thermal

emittanceassociated 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 dailyoot 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 andresources 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 .

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 heatcapacities, surace roughness, heat transer

rates, thermal emittance, and permeability

aect pavement temperatures.

http://www.epa.gov/heatisland/index.htmhttp://www.epa.gov/heatisland/index.htmhttp://www.epa.gov/heatisland/index.htmhttp://www.epa.gov/heatisland/index.htm


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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 temperatures. 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 , and or inormation on vegetated sur

aces, see the Trees and Vegetation chapter o this compendium.

Figure 3: Solar Energy versus Wavelength Reaching Earths Surace on a Typical Clear Summer Day

1.000.900.800.700.600.500.400.300.200.100.00

0 200 400 600 800 100012001400160018002000220024002600

ultraviolet visible infrared

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.)

NormalizedSolarIntensity

http://www.epa.gov/smartgrowthhttp://www.epa.gov/smartgrowth


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Time in years

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 orays 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 Earths surace on a clear

summer day.

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

10has ocused on this property, and it is the5main determinant o a materials maximum

Most existing research on cool pave

ments ocuses on solar refectance,

which is the primary determinant o

a materials 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 Time45

40

Concrete pavements

Asphalt pavements

Solarreflectancein%

35

30

25

20

15

surace temperature.6Albedo 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 todetermine 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 atmosphere. (See Figure 4.) However, as Figure 4

also shows, these values depend on age and

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 materials 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

ASUNationalCenteroExcelle

nce

Albedo alone can signicantly inuence surace temperature, with the white stripe on the brick wall about 510F

(35C) cooler than the surrounding, darker areas.

1.3 Thermal Emittance

A materials thermal emittance determineshow 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 Table1 on page 7, ASTM methods can be used to

measure this property.

Thermal emittance plays a role in determin

ing a materials contribution to urban heatislands. 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.9Although 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 highemittance values.10



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Standards or Measuring Solar Reectance and ThermalEmittance

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 materials temperaturein 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 Test Method Equipment Used Test Location

Solar reectance ASTM E 903 - Standard Test Method

or Solar Absorbance, Reectance,

and Transmittance o Materials Using

Integrating Spheres.

Integrating sphere spectro

photometer

Laboratory

Solar reectance ASTM C 1549 - Standard Test Method

or Determination o Solar Reectance

Near Ambient Temperature Using a

Portable Solar Reectometer

Portable solar reectometer Laboratory or

eld

Solar reectance ASTM E 1918 - Standard Test Method

or Measuring Solar Reectance o

Horizontal and Low-Sloped Suraces in

the Field

Pyranometer Field

Total emittance ASTM E408-71 - Standard Test Methods

or Total Normal Emittance o Suraces

Using Inspection-Meter Techniques

Portable, inspection-meter

instruments

Laboratory or

eld

Solar reectance

index

ASTM E 1980 - Standard Practice or

Calculating Solar Reectance Index o

Horizontal and Low-Sloped Opaque

Suraces

None (calculation)



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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 concrete 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 Figure 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

Figure 6: Permeable versus

Conventional Asphalt

contain grass or low-lying vegetation, which

can stay particularly cool because the surace temperature o well-hydrated vegeta

tion typically is lower than the ambient air

temperature.

Permeable asphalt (oreground) allows water to

drain rom the surace and into the voids in the

pavement, unlike conventional asphalt (mid- and

background).

DepartmentoAgric

ulture

U.S.



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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 pavements surace

(and increasing daytime surace tempera

tures), but reducing bulk heat storage (re

ducing release o heat at nighttime).13The

larger surace area also may help increase

air movementconvectionover 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 duringthe nighttime. Release o stored heat rom

urban materials is a signicant contributor

to the nighttime heat island experienced in

many cities.

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 pavementsunction, 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 ismoist, 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.

Water Retentive Pavements

and Water Sprinkling inJapan

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 capillaryaction 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 havebeen eective in keeping pavement

temperatures low.14

Besides solar refectance, emittance, and

permeability, other properties and actors

infuence how readily pavements absorb or

lose heat.

Convection. Pavement transers heat tothe 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



13/39

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

aces net solar refectance.

Thermal Conductivity. Pavement withlow 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 materials, 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 suns

energysometimes retaining twice asmuch as their rural surroundings dur

ing daytime.15The 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 pavement also infuences how much heat it

will store, with thicker pavements stor

ing more heat.16

Urban Geometry.The dimensions andspacing 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 thatis 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.

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, withthe 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, haveestimated that every 10 percent increase

in solar refectance could decrease sur

ace temperatures by 7F (4C). 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 1F (0.6C).17 Earlier research analyzed

a combination o mitigation measures in

the Los Angeles area, including pavement

and roong solar refectance changes, andincreased use o trees and vegetation. The

study identied a 1.5F (0.8C) temperature

improvement rom the albedo changes.18A

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



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Figure 7: Urban Canyons

MarkMeier

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 establishedsuchas conventional concrete, which initially

has a high solar refectance. Others are

emergingsuch 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

uses. Some are best or light trac areas,

or example. Further, depending on local

conditionssuch as available materials,

labor costs, and experience with dierent

applicationscertain 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 opavement 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.



15/39

0

10

Figure 8: Percentage o Pavement Area by Type Nonvegetated permeable pavementso Use21 contain voids and are designed to allow

60 water to drain through the surace into

the sublayers and ground below. These50

materials can have the same structural40 integrity as conventional pavements.

Roads

Percentag

e

30 Parking For example, some orms o porousSidewalks pavements, such as open-graded ric

20 Other

tion course (OGFC) asphalt pave-

ModifedromL

BNL

ments, have been in use or decades

to improve roadway riction in wetSacramento Chicago Salt Lake Houston

weather.22 Recently, rubberized asphalt

has been used on roads and highways

City

CitiesLBNL 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,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.

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.

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,whichuse clear tree resins in place o

petroleum-based elements to bind

an aggregate

Colored asphalt and colored con-

crete,with added pigments or seals

to increase refectance

to reduce noise, and pervious concrete

applications are being studied or road

way use. For some permeable pavement

options, the typical use may be orlower trac areas such as parking lots,

alleys, or trails. Examples o nonveg

etated permeable pavements include:

Porous asphalt

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

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, thesematerials 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.



16/39

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 24

inches (510 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 location-

specic 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.

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 therefectivity 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 producing Portland cement. Because o

such benets, Caliornias 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 Table2 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



17/39

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.

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.)



18/39

Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications

NEW CONSTRUCTION

Pavement Type Description o

Technology

Properties to Consider Pavement Temperature

Impacts

Urban Climate Impacts Issu

Co

Reective Pavement Options

Asphalt pavement, Asphalt pavements Solar reectance, + Lowers pavement + Can contribute to Smodied with high consist o an asphalt which initially may temperature because lower air tempera-

albedo materials or binder mixed with sand be 5%, can increase more o the suns tures day and night, a

treated ater installation or stone, reerred to as to 1520% as con- energy is reected although air tempera- a

to raise albedo. aggregate. ventional asphalt

ages. 27

Using light-coloredaggregate, color pig

ments, or sealants,

the reectance o

conventional asphalt

can be increased.

Maintenance applications such as

chip seals also can

increase solar reec

tance. (See below.)

Urban geometry caninuence the eect

o high albedo pave

ments.

away, and there is less

heat at the surace to

absorb into the pave

ment.

tures are not directly

related to surace

temperatures and

many complicating

actors are involved.28

Reected heat can be

absorbed by the sides

o surrounding build

ings warming the in

terior o the building

and contributing to

the nighttime urban

heat island eect,

due to the additional

heat that needs to be

released rom urban

inrastructure.

a

c

t

t

cOOlPAVeMeN

tsdRAFt

15


19/39

Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)NEW CONSTRUCTION (continued)


Technology


Impacts


Con

Reective Pavement Options (continued)

Concrete: Portland cement mixed Initial solar reec + Lowers pavement + Can contribute to Conventional with water and ag tance can be 40%. temperature because lower air tempera-Modied gregate. Cured until it is

strong enough to carry

trafc.

This can be raisedto more than 70%

using white cement

instead o gray ce

ment mixtures.30


o high-albedo pavements.

more o the suns

energy is reected


heat at the surace to

absorb into the pave

ment.

tures day and night,

although air tempera


related to surace

temperatures and

many complicating

actors are involved.

Reected heat can beabsorbed by the sides

o surrounding build

ings warming the in


and contributing to

the nighttime urban

heat island eect,



released rom urban

inrastructure.

RedUcING

URBAN

HeAtIslANdsdRAFt

16


20/39

Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)

NEW CONSTRUCTION (continued)


Technology


Impacts


Con


Other refective Resin based pave These alternative + Lowers pavement + Can contribute to pavements: ments use clear pavements will have temperature because lower air tempera-

Resin based colored tree resins in varying solar reec more o the suns tures day and night, Colored asphalt place o cement to tances based on the energy is reected although air tempera-Colored concrete bind the aggregate,

thus albedo is mainly

determined by ag

gregate color.

Colored asphalt orconcrete involve pig

ments or seals that

are colored and may

be more reective

than the conven

tional equivalent.

These can be applied

when new or during

maintenance.

materials used to

construct them.


high-albedo pave

ments have.


heat at the surace

to absorb into the

pavement.


related to surace

temperatures and

many complicating


Reected heat can be


o surrounding build

ings warming the in


and contributing to

the nighttime urban

heat island eect,



released rom urban

inrastructure.

cOOlPAVeMeN

tsdRAFt

17


21/39

Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)NEW CONSTRUCTION (continued)


Technology


Impacts


Con

Permeable Pavement Options

Nonvegetated perme- Porous asphalt has Provides cool + When wet, lowers + When moist, can able pavements more voids than con

ventional asphalt to

allow water to drain

through the surace

into the base.

Rubberized asphalt,or crumb rubber, in

volves mixing shred

ded rubber intoasphalt. This material

is generally used to

reduce noise.

Other porousasphalts or open-

grade course riction

suraces can also be

used or reducing

noise. 32

ing through

evaporation.

Solar reectance othese materials de

pends on individual

materials (e.g., gravel

may be white and

very reective). In

general, permeablepavements may be

less reective than

their nonpermeable

equivalent due to

the increased surace

area.33

Increased convection may help cool

the pavement due

to increased surace

area. 34

pavement tempera

ture through evapora

tive cooling.

When dry, may be hot

at the surace, but

subsurace generally

will be same tempera

ture as nonpermeable

equivalent.

contribute to lower

air temperatures day

and night, through

evaporative cooling,



related to surace

temperatures and

many complicatingactors are involved.

When dry, can

contribute to higher

daytime surace

temperatures, but

may not aect or may

even reduce night

time air temperatures,



related to surace

temperatures and

many complicating


RedUcING

URBAN

HeAtIslANdsdRAFt

18


22/39


NEW CONSTRUCTION (continued)


Technology


Impacts


Con

Permeable Pavement Options (continued)

Nonvegetated

permeable pavements

(continued)Pervious concretehas more voids than

conventional con

crete to allow water

to drain through

the surace into the

base.

Brick or block paversare generally made

rom clay or concrete

blocks lled with

rocks, gravel, or soil.

(see prior page) (see prior page) (see prior page) (se

Vegetated permeable

pavements:

Grass paversConcretegrid pavers

Plastic, metal, orconcrete lattices

provide support and

allow grass or other

vegetation to grow

in the interstices.

Provides coolingthrough evapotrans

piration.

Sustainability ovegetation may vary

with local conditions.

+ Lowers pavement

temperatures

through evapotrans

piration, particularly

when moist.

+ When dry may

still be cooler than

other pavement

options due to the

natural properties o

vegetation.

+ In most conditions

will contribute to

lower air tempera


through evapo

transpiration and

natural properties o

vegetation. Mois

ture availability will

greatly increase its

eectiveness.

cOOlPAVeMeN

tsdRAFt

19


23/39

Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)MAINTENANCE/REHABILITATION


Technology


Impacts


Con

Reective Pavement Options

Chip seals made with Chip seals describe Solar reectance o + Lowers pavement sur + Can contribute to high-albedo aggregate aggregate used to

resurace low-

volume asphalt

roads and some

times or highway

suraces.

chip seals will corre

late with the albedo

o the aggregate

used. In San Jose, CA,

researchers identi

ed albedo o 20%

or new chip seals,

which then decline

with age.37


high-albedo pave

ments have

ace and subsurace

temperature because

more o the suns

energy is reected


heat at the surace

to absorb into the

pavement.

lower air tempera




related to surace

temperatures and

many complicating


Reected heat can beabsorbed by the sides

o surrounding build

ings warming the in


and contributing to

the urban heat island

eect.

RedUcING

URBAN

HeAtIslANdsdRAFt

20


24/39


MAINTENANCE/REHABILITATION (continued)


Technology


Impacts


Con


Whitetopping Whitetopping is athick layer (thick

ness greater than

4 inches or 10 cm)

o concrete applied

over existing asphalt

when resuracing

or can be applied to

new asphalt. It oten

contains bers or

added strength.

Ultra-thin whitetopping is generally 24

inches (510 cm)

thick and similar to

whitetopping.

The solar reectanceo whitetopping

material can be as

high as concrete.

Urban geometrycan inuence the

eect o high-albedo

pavements.

+ Lowers pavement sur

ace and subsurace

temperature because

more o the suns

energy is reected


heat at the surace

to absorb into the

pavement.

+ Can contribute to

lower air tempera




related to surace

temperatures and

many complicating


Reected heat can be


o surrounding build

ings, warming the in


and contributing to

the urban heat island

eect.

cOOlPAVeMeN

tsdRAFt

21


25/39

Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)MAINTENANCE/REHABILITATION (continued)


Technology

Properties to Consider Pavement Tempera

ture Impacts

Urban Climate Impacts Issues and

ations


Microsuracing Athinsealing Solarreectanceof + Lowers pavement + Can contribute to lower Solarrewith high- layer used or road microsuracing will cor- surace and sub- air temperatures day and may decr

albedo materials maintenance.

Light-coloredmaterials can be

used to increase

the solar reec

tance o asphalt.

relate with the albedo

o the materials used.

Researchersrecently measured solar reec

tances o microsurac

ing applications over

35%.38

surace tempera

ture because more

o the suns energy

is reected away,

and there is less

heat at the surace

to absorb into the

pavement.

night, although air tem

peratures are not directly

related to surace tempera

tures and many complicat

ing actors are involved.

Reected heat can be

absorbed by the sides o

surrounding buildings,warming the interior o the

building and contributing

to the urban heat island

eect.

time, i so

trafc ma

albedo m

ing mate

Urbange

particula

canyons,

the impaalbedo pa

have on t

climate.RedUcING

URBAN

HeAtIslANdsdRAFt

22


26/39

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 givesexamples where available. Again, decision-

makers 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 1F (0.6C), which would resultin 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 otherenergy 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

Measuring Energy Savings

rom Cool Roos versusCool 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 withcool 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 tempera-

tureswhether due to high solar refec

tance, permeability, or other actorscan

help lower the temperature o stormwater

runo, thus ameliorating thermal shock to



27/39

aquatic lie in the waterways into which

stormwater drains.42 Laboratory tests with

permeable pavers have shown reductions

in runo temperatures o about 37F

(24C) 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.

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 20F (11C) cooler lasted 10

times longer than the hotter pavements,

and pavements that were 40F (22C) cool

er lasted 100 times longer beore showing

permanent damage.47

Quality o Lie BeneftsCool 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

Figure 9: Slag Cement Airport Expansion

SlagCementAssociation

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

Comort improvements. Using refec

tive or permeable pavements where

people congregate or children play

can provide localized comort benets

through lower surace and near-suraceair temperatures.50

Noise reduction.The open pores opermeable pavements, such as an open-

graded 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

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



28/39

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

Table 3: Comparative Costs o Various Pavements56

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 actorsas highlighted

abovewill 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.

Basic Pavement Types Example Cool Approaches

Approximate

Installed Cost,

$/square oot*

Estimated Service

Lie, Years

New Construction

Asphalt (conventional) Hot mix asphalt with light aggregate, $0.10$1.50 720

i locally available

Concrete (conventional) Portland cement, plain-jointed $0.30$4.50 1535

Nonvegetated permeable pave- Porous asphalt $2.00$2.50 710

ment Pervious concrete $5.00$6.25 1520

Paving blocks $5.00$10.00 > 20

Vegetated permeable pave- Grass/gravel pavers $1.50$5.75 > 10

ment

Surace applications Chip seals with light aggregate, i $0.10$0.15 28

locally available

Microsuracing $0.35$0.65 710

Ultra-thin whitetopping $1.50$6.50 1015

Maintenance

* Some technologies, such as permeable options, may reduce the need or other inrastructure, such as stormwater

drains, thus lowering a projects overall expenses. Those savings, however, are not reected in this table. (1 square oot

= 0.09 m2)



29/39

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 orEnvironmental 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.

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 toinormation 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 Universitys NationalCenter o Excellence (NCE) SMART

Innovations or Urban Climate and

Energy.59This group is studying established 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 SciencesTransportation 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 incool 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



30/39

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

Chicagos Green Alley program aims

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 otherbenets.62

Environmental rating programs suchas 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.

Growing Concern about

Synthetic Tur

Many communities have begun toexamine 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 60F (16C) 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 ohow dierent materials interact with

the urban climate.63

Figure 11: Grass Paving

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.

DavidHitchcock,

HARC



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Alternative Paving under the Cool Houston Plan

While most communities have no, or limited, cool pavement experience, Houstons

heat island initiative recommends alternative pavements as part o the citys overallapproach to improving air quality and public health. The plans three-tiered strategy

includes:

Targeting alternative paving options or specic types o paved suraces, such ashighways 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, environmentalmanagement, and public works maintenance benets o alternative pavements.

Combining and embedding alternative paving incentives into larger programsand regulations, such as meeting Clean Air or Clean Water Act standards, with thesupport o the Greater Houston Builders Association and the Texas Aggregates

and Concrete Association.

Table 4: Examples o Cool Pavement Initiatives

Type o

Initiative Description Links to Examples

Research Industry Since 1928, the National Ready Mixed Concrete Associations

research laboratory has helped evaluate materials and set technical standards. Recent

projects include developing permeability tests and assessing concrete with high y-ash content.

National

laboratory

Th e Heat Island Group at Lawrence

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-

supported

and similar

consortia

Arizona State Universitys National Center

o Excellence collaborates with industry and government to research and develop

technologies to reduce urban heat islands, especially in desert climates.

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.

http://www.nrmca.org/%3E%E2%80%94http://eetd.lbl.gov/HeatIsland/Pavements/%3E%E2%80%94http://www.asusmart.com/pavements.php%3E%E2%80%94http://www.harc.edu/Projects/CoolHouston/%3E%E2%80%94http://ncsu.edu/picp/index.htmlhttp://www.bae.ncsu.edu/info/permeable_pavement/index.html%3E%E2%80%94http://www.bae.ncsu.edu/info/permeable_pavement/index.html%3E%E2%80%94http://www.bae.ncsu.edu/info/permeable_pavement/index.html%3E%E2%80%94http://www.bae.ncsu.edu/info/permeable_pavement/index.html%3E%E2%80%94http://ncsu.edu/picp/index.htmlhttp://www.harc.edu/Projects/CoolHouston/%3E%E2%80%94http://www.asusmart.com/pavements.php%3E%E2%80%94http://eetd.lbl.gov/HeatIsland/Pavements/%3E%E2%80%94http://www.nrmca.org/%3E%E2%80%94


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Table 4: Examples o Cool Pavement Initiatives (cont.)

Type o

Initiative Description Links to Examples

Voluntary

eorts

Demonstration

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 &

education

< www.epa.gov/heatisland/>EPAs Heat Island Reduction Initiative provides inor

mation on the temperature, energy, and air quality impacts rom cool pavements and

other heat island mitigation strategies.

EPAs 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 partnerships 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 The National Institute o Standards and

Technology (NIST) has developed a sotware tool, Building or Environmental andEconomic Stability (BEES). The tool enables communities to conduct lie cycle cost

assessments or various types o building initiatives, including pavement projects.

Policy

eorts

Municipal

regulations that

support cool

pavements

Th e Cool Hous

ton! Plan promotes cool paving as well as other techniques to reduce the regions

heat island.

Torontos Design Guidelines or Greening Surace Parking Lots encourage reective

and permeable pavements to reduce surace temperatures.

Although cool pavements are still in their

inancy compared with the other heatisland mitigation strategiestrees and veg

etation, green roos, and cool roosinter

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,

heat-health, and other concerns, communi

ties can expect to see more cool pavementinstallations. 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.

http://www.cityofpoulsbo.com/CityCouncil/PDFsDOCs/Works/2007/4-25minutes.pdf%3E%E2%80%94http://www.heifer.org/site/c.edJRKQNiFiG/b.1484715/%3E%E2%80%94http://www.epa.gov/heatisland/%3E%E2%80%94http://cfpub.epa.gov/npdes/home.cfm?program_id=298%3E%E2%80%94http://www.greenhighways.org/%3E%E2%80%94http://nemo.uconn.edu/index.htm%3E%E2%80%94http://www.bfrl.nist.gov/oae/software/bees/%3E%E2%80%94http://files.harc.edu/Projects/CoolHouston/CoolHoustonPlan.pdf%3E%E2%80%94http://www.toronto.ca/planning/urbdesign/greening_parking_lots.htm%3E%E2%80%94http://www.toronto.ca/planning/urbdesign/greening_parking_lots.htm%3E%E2%80%94http://files.harc.edu/Projects/CoolHouston/CoolHoustonPlan.pdf%3E%E2%80%94http://www.bfrl.nist.gov/oae/software/bees/%3E%E2%80%94http://nemo.uconn.edu/index.htm%3E%E2%80%94http://www.greenhighways.org/%3E%E2%80%94http://cfpub.epa.gov/npdes/home.cfm?program_id=298%3E%E2%80%94http://www.epa.gov/heatisland/%3E%E2%80%94http://www.heifer.org/site/c.edJRKQNiFiG/b.1484715/%3E%E2%80%94http://www.cityofpoulsbo.com/CityCouncil/PDFsDOCs/Works/2007/4-25minutes.pdf%3E%E2%80%94


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5 Resources

The organizations below may provide additional inormation on alternative, or cool,

pavement technologies.

Program/Organization Role Web Address

The Federal Highway

Administrations (FHWA)

Ofce o Pavement

Technology

The Ofce o Pavement Technology conducts research

and training related to asphalt and concrete pavements.

FHWAs Ofce o Planning,

Environment, and Realty

This ofces Web site provides inormation regarding

transportation planning and the environment.

American Association

o State Highway and

Transportation Ofcials

Center or Environmental

Excellence (AASHTO)

AASHTO created the Center or Environmental Excellence

in cooperation with the Federal Highway Administration

to oer technical assistance about environmental

regulations and ways to meet them.

Association o Metropolitan

Planning Organizations

(AMPO)

AMPO supports local MPOs through training,

conerences, and assistance with policy development.

The American Concrete

Pavement Association (ACPA)

ACPA promotes concrete pavement by working with

industry and government.

The Asphalt Pavement

Alliance (APA)

A consortium o the National Asphalt Paving Association

(NAPA), the Asphalt Institute (AI), and state paving

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

Pavement Institute (ICPI)

ICPI has a document that compares permeable pavement

technologies and helps readers nd certied installers.

National Center or Asphalt

Technology (NCAT)

NCAT provides up-to-date strategies or designing and

constructing asphalt pavements.

National Ready Mixed

Concrete Association

Since 1928, the National Ready Mixed Concrete

Associations 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)

PCA represents cement companies in the United Statesand Canada and conducts research, development, and

outreach.

http://www.fhwa.dot.gov/pavement/hq/welcome.cfmhttp://www.fhwa.dot.gov/pavement/hq/welcome.cfmhttp://www.fhwa.dot.gov/pavement/hq/welcome.cfmhttp://www.fhwa.dot.gov/hep/index.htmhttp://www.fhwa.dot.gov/hep/index.htmhttp://environment.transportation.org/http://environment.transportation.org/http://www.ampo.org/http://www.pavement.com/http://www.asphaltalliance.com/http://www.asphaltalliance.com/http://www.icpi.org/http://www.ncat.us/http://www.nrmca.org/http://www.cement.org/http://www.cement.org/http://www.nrmca.org/http://www.ncat.us/http://www.icpi.org/http://www.asphaltalliance.com/http://www.asphaltalliance.com/http://www.pavement.com/http://www.ampo.org/http://environment.transportation.org/http://environment.transportation.org/http://www.fhwa.dot.gov/hep/index.htmhttp://www.fhwa.dot.gov/hep/index.htmhttp://www.fhwa.dot.gov/pavement/hq/welcome.cfmhttp://www.fhwa.dot.gov/pavement/hq/welcome.cfmhttp://www.fhwa.dot.gov/pavement/hq/welcome.cfm


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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. 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 CaseStudy 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.

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 Report. Prepared or

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 Pavement Surace Temperatures. Solar

Energy. 81(7): 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 , and state and ederal government sites, among others, dene as

phalt. Two useul ones are and

.

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 Most During Day and Night? Case Study

1(1).

10 Levinson, R., H. Akbari, S. Konopacki, and S. Bretz. 2002. Inclusion o Cool Roos in Nonresi

dential Title 24 Prescriptive Requirements. Paper LBNL-50451. Lawrence Berkeley NationalLaboratory, 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 Transportation Research Board Annual Meeting.

http://ams.confex.com/ams/pdfpa%EF%BF%BDrs/79804.pdfhttp://ams.confex.com/ams/pdfpa%EF%BF%BDrs/79804.pdfhttp://www.cement.org/tech/cct_concrete_prod.asphttp://www.cement.org/tech/cct_concrete_prod.asphttp://www.virginiadot.org/business/resources/bu-mat-Chapt1AP.pdfhttp://www.tfhrc.gov/hnr20/recycle/waste/app.htmhttp://www.tfhrc.gov/hnr20/recycle/waste/app.htmhttp://www.virginiadot.org/business/resources/bu-mat-Chapt1AP.pdfhttp://www.cement.org/tech/cct_concrete_prod.asphttp://www.cement.org/tech/cct_concrete_prod.asphttp://ams.confex.com/ams/pdfpa%EF%BF%BDrs/79804.pdfhttp://ams.confex.com/ams/pdfpa%EF%BF%BDrs/79804.pdfhttp://ams.confex.com/ams/pdfpa%EF%BF%BDrs/79804.pdf


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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 Japans 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 .

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 .

15 Christen, A. and R. Vogt. 2004. Energy and radiation balance o a Central European city. International Journal o Climatology. 24(ii):1395-1421.

16 Golden,

Documents

Reducing Urban Heat Islands: Cool Pavements