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8/9/2019 Reducing Urban Heat Islands: Cool Pavements
1/39
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
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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.
cOOl PAVeMeNts dRAFt 3
http://www.epa.gov/heatisland/index.htmhttp://www.epa.gov/heatisland/index.htmhttp://www.epa.gov/heatisland/index.htmhttp://www.epa.gov/heatisland/index.htm8/9/2019 Reducing Urban Heat Islands: Cool Pavements
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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
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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
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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.
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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.
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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
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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.)
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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
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)NEW CONSTRUCTION (continued)
Pavement Type Description o
Technology
Properties to Consider Pavement Temperature
Impacts
Urban Climate Impacts Issu
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
Urban geometry caninuence the eect
o high-albedo pavements.
more o the suns
energy is reected
away, and there is less
heat at the surace to
absorb into the pave
ment.
tures day and night,
although air tempera
tures are not directly
related to surace
temperatures and
many complicating
actors are involved.
Reected heat can beabsorbed 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.
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)
NEW CONSTRUCTION (continued)
Pavement Type Description o
Technology
Properties to Consider Pavement Temperature
Impacts
Urban Climate Impacts Issu
Con
Reective Pavement Options (continued)
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.
Urban geometry caninuence the eect
high-albedo pave
ments have.
away, and there is less
heat at the surace
to absorb into the
pavement.
tures are not directly
related to surace
temperatures and
many complicating
actors are involved.
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.
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)NEW CONSTRUCTION (continued)
Pavement Type Description o
Technology
Properties to Consider Pavement Temperature
Impacts
Urban Climate Impacts Issu
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,
although air tempera
tures are not directly
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,
although air tempera
tures are not directly
related to surace
temperatures and
many complicating
actors are involved.
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)
NEW CONSTRUCTION (continued)
Pavement Type Description o
Technology
Properties to Consider Pavement Temperature
Impacts
Urban Climate Impacts Issu
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
tures day and night,
through evapo
transpiration and
natural properties o
vegetation. Mois
ture availability will
greatly increase its
eectiveness.
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)MAINTENANCE/REHABILITATION
Pavement Type Description o
Technology
Properties to Consider Pavement Temperature
Impacts
Urban Climate Impacts Issu
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
Urban geometry caninuence the eect
high-albedo pave
ments have
ace and subsurace
temperature because
more o the suns
energy is reected
away, and there is less
heat at the surace
to absorb into the
pavement.
lower air tempera
tures day and night,
although air tempera
tures are not directly
related to surace
temperatures and
many complicating
actors are involved.
Reected heat can beabsorbed by the sides
o surrounding build
ings warming the in
terior o the building
and contributing to
the urban heat island
eect.
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)
MAINTENANCE/REHABILITATION (continued)
Pavement Type Description o
Technology
Properties to Consider Pavement Temperature
Impacts
Urban Climate Impacts Issu
Con
Reective Pavement Options (continued)
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
away, and there is less
heat at the surace
to absorb into the
pavement.
+ Can contribute to
lower air tempera
tures day and night,
although air tempera
tures are not directly
related to surace
temperatures and
many complicating
actors are involved.
Reected heat can be
absorbed by the sides
o surrounding build
ings, warming the in
terior o the building
and contributing to
the urban heat island
eect.
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Table 2: Properties that Inuence Pavement TemperaturesImpacts and Applications (continued)MAINTENANCE/REHABILITATION (continued)
Pavement Type Description o
Technology
Properties to Consider Pavement Tempera
ture Impacts
Urban Climate Impacts Issues and
ations
Reective Pavement Options (continued)
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
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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
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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
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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)
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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
RedUcING URBAN HeAt IslANds dRAFt26
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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.
RedUcING URBAN HeAt IslANds dRAFt28
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%948/9/2019 Reducing Urban Heat Islands: Cool Pavements
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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.
cOOl PAVeMeNts dRAFt 29
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%948/9/2019 Reducing Urban Heat Islands: Cool Pavements
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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.
RedUcING URBAN HeAt IslANds dRAFt30
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.cfm8/9/2019 Reducing Urban Heat Islands: Cool Pavements
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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.
cOOl PAVeMeNts dRAFt 31
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.pdf8/9/2019 Reducing Urban Heat Islands: Cool Pavements
35/39
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,