The Sustainable Pavement - Asphalt Pavement … safety Smooth asphalt roads give vehicle tires...

The Sustainable PavementASPHALT

for constructingpavements. From the productionof the paving material, to theplacement of the pavement on theroad, to rehabilitation, throughrecycling, asphalt pavements mini-mize impact on the environment.Low consumption of energy forproduction and construction, lowemission of greenhouse gases,and conservation of naturalresources help to make asphalt theenvironmental pavement of choice.

ENERGY & RECYCLING PERFORMANCE WATER QUALITY CLEAN AIR & COOL CITIES

SMOOTH | QUIET | DURABLE | SAFE www.asphaltalliance.com

Asphalt is thesustainablematerial

Less energy consumed in building pavementsAsphalt pavements require about 20 percentless energy to produce and construct than otherpavements.1

Less energy consumed by thetraveling publicCongestion leads to unnecessary consumptionof fuel and production of emissions. Reducingcongestion by constructing asphalt pavementsjust makes sense. Asphalt pavements are fasterto construct and rehabilitate. And, a new or

newly rehabilitated asphalt pavement can beopened to traffic as soon as it has been com-pacted and cooled. There is no question ofwaiting for days or weeks for the material tocure.

America’s leading recyclerAccording to an EPA/FHWA study,2 the asphaltindustry recycles more than 70 million tons ofits own product every year, making it America’snumber one recycler. Asphalt recycling savestaxpayers about $1.8 billion a year.

Other materials are routinely recycled intoasphalt pavements. Some of the most commonare rubber from used tires, glass, asphalt roofing shingles, and blast furnace slag.

Energy and Recycling

The road doesn’t wear outAsphalt is the Perpetual Pavement. When appro-priately designed and constructed, the roaditself doesn’t wear out. Maintenance is simple:only the top layer is removed and replaced.This can be done quickly, even overnight, andit saves taxpayers money. The material that hasbeen reclaimed is then recycled. The newlyoverlaid road surface (which may also containrecycled material) is a good-as-new pavement.Total removal and reconstruction is not needed.This is a truly sustainable construction process.

Rubblizing for sustainabilityWhen concrete pavements reach the end oftheir useful life, they must undergo expensiverehabilitation—unless they are rehabilitatedthrough a sustainable process called

rubblization. Theworn-out concreteis “rubblized” (fractured) andbecomes the basefor the newasphalt road. Thissaves fuel thatwould have beenused by truckshauling the oldmaterial away;

saves the virgin materials that would have beenneeded to build a new road base; and can givethe traveling public a new Perpetual Pavement.In addition to the environmental and speed ofconstruction advantages, cost savings can besignificant.

SMOOTH | QUIET | DURABLE | SAFE

Performance

Public safetySmooth asphalt roads give vehicle tires superiorcontact with the road, improving safety.

Open-graded asphalt allows rainwater to drainthrough the pavement surface, reducing theamount of splash and spray kicked up by vehicles.

Noise reductionAsphalt is the quiet pavement. Newer quietpavement technologies include fine-gradeddense pavements, open-graded surfaces, andtwo-layer open-graded pavements.3 Studiesshow that the noise-reducing properties ofasphalt last for many years.4 Noise reduction of3 to 10 dB(a) are common. Reducing noise by

3 dB(a) is about the same as doubling the distance from the road to the listener, or reducing traffic volume by 50 percent.

Asphalt moves traffic alongAsphalt pavements are faster to construct andrehabilitate. In crowded urban areas, where clos-ing a road for rehabilitation or reconstructionwould dump increased traffic on neighboringroutes, asphalt is the answer. Highways androads can be milled for recycling, then overlaid, during off-peak hours. An entire freeway canbe resurfaced without commuters ever beinginconvenienced.

Water QualityStormwatermanagementwith porousasphaltPorous asphalt pave-ment systems canreplace impermeablesurfaces for parkinglots, roads, walk-ing/biking paths,

and other applications. Porous pavements canturn runoff into infiltration; restore the hydrolo-gy of a site, or even improve it; improve waterquality; and eliminate the need for detentionbasins.5

Asphalt pavements do not leachOnce constructed, asphalt pavements have min-imal impact on the environment. Studies showthat asphalt pavements and stockpiles ofreclaimed asphalt pavement do not leach.6, 7

EnvironmentalapplicationsAsphalt is used toconstruct liners andcaps for landfills. Theimpermeable materialis an effective barrierto potential leaks.

Drinking water reservoirs are often lined with asphalt. Asphalt cement is also used to line water pipes that supply potable water to humans.

Oregon and Washington state fish and wildlife agencies use asphalt pavement to line their fish rearing ponds.8

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Asphalt plants are environmentally soundEmissions from asphalt plants, including green-house gases, are very low and well-controlled.Since 1970, the asphalt industry has decreasedtotal emissions from plants by 97 percent whileincreasing production by 250 percent.9

Emissions from asphalt plants are so low, theEPA considers them as onlyminor sources of industrial pollution.10

Cool CitiesThe urban heat island effectis not a black and whiteissue. 11 Porous asphalt pave-ments have been shown tolower nighttime surface temperatures as comparedto impervious pavements.In at least one city, thehottest heat signature is atthe airport, with its thick,dense, impervious runways.

Traffic reliefWhen cars and trucks are mired in congestion,they consume fuel and produce greenhousegases. Asphalt’s speed of construction allowsplanners and managers a way to fix congestionhot spots and bottlenecks, quickly and cost-effectively.


Clean Air & Cool Cities

R E F E R E N C E S1. Gambatese, John A. and Sathyanarayanan Rajendran,“Sustainable Roadway Construction: Energy Consumption andMaterial Waste Generation of Roadways,” American Society ofCivil Engineers, Reston, VA. Proceedings of 2005 ConstructionResearch Congress.(http://www.pubs.asce.org/WWWdisplay.cgi?0520020.Downloaded June 22, 2006.)

2. A Study of the Use of Recycled Paving Material: Report toCongress, June 1993, Federal Highway Administration and UnitedStates Environmental Protection Agency, Washington, DC. FHWA-RD-93-147 and EPA/600/R-93/095.

3. Newcomb, Dave, and Larry Scofield, “Quiet Pavements Raisethe Roof in Europe,” Hot Mix Asphalt Technology, National AsphaltPavement Association, Lanham, MD, September/October 2004.

4. Reyff, James, et al., I-80 Davis OGAC Pavement Noise Study:Traffic Noise Levels Associated With an Open Grade AsphaltConcrete Overlay. Prepared for California Department ofTransportation by Illingworth & Rodkin, Inc., Sacramento, CA,December 1, 2002.

5. Jackson, Newt, Design, Construction and Maintenance Guidefor Porous Asphalt Pavements (IS-131), National Asphalt PavementAssociation, Lanham, MD, 2003.

6. Kriech, AJ, et. al. “Determination of polycyclic aromatic com-pounds in asphalt and in corresponding leachate water.” PolycyclicAromatic Compounds, Taylor & Francis Group, Philadelphia, PA.Volume 22, Numbers 3-4, pp. 517-535. 2002.

7. Townsend, Timothy, and Allen Brantley. Leaching Characteristicsof Asphalt Road Waste. University of Florida, 1998.(http://www.hinkleycenter.com/publications/townsend_98-2.pdf,accessed September 1, 2006)

8. Environmental Applications for Hot Mix Asphalt (PR-1). AsphaltInstitute, Lexington, KY. Undated.

9. Report to Members 2001, National Asphalt PavementAssociation, Lanham, MD. 2002.

10. Federal Register, February 12, 2002, pp. 6521 ff.(http://frwebgate.access.gpo.gov/cgi-bin/getpage.cgi?dbname=2002_register&position=all&page=6521,accessed September 7, 2006.)Also, Federal Register, November 8, 2002, pp. 68124 ff.

(http://frwebgate.access.gpo.gov/cgi-bin/getpage.cgi?dbname=2002_register&position=all&page=68124, accessed September 7, 2006.)

11. Golden, Jay, and Kamil Kaloush, “A Hot Night in the Big City:How to Mitigate the Urban Heat Island,” Public Works, December2005. (http://www.pwmag.com/industry-news.asp?sectionID=770&articleID=268116, accessed September5, 2006)

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Lower greenhouse gases, lowerfuel consumptionThe production and placement of asphaltpavements consumes less fuel and pro-duces lower levels of greenhouse gases.According to a recent study, asphalt pave-ments require about 20 percent less ener-gy to produce and construct than otherpavements.

1Less fuel consumption means

less production of carbon dioxide andother greenhouse gases.

Since 1970, the asphalt industry hasdecreased total emissions from plants by97 percent while increasing production by250 percent.

2Emissions from asphalt

plants are so low, the EPA considers themas only minor sources of industrial pollution.

3

The asphalt industry is also working onways to reduce the temperatures at whichasphalt pavements are produced andplaced. Typically, asphalt paving tempera-tures are in the range of 280 to 320°F.Lowering these temperatures by 50°F ormore would save fuel and reduce produc-tion of greenhouse gases and other emis-sions. Working in cooperation with theFederal Highway Administration, stateDepartments of Transportation, and otherkey stakeholders, the asphalt industry’sresearch on several new warm-mix tech-nologies holds great future promise.

Asphalt moves traffic alongWhen traffic backs up, cars and trucksconsume fuel unnecessarily and produceexcess emissions. One way to reduceboth fuel consumption and emissions is

to keep traffic moving along. Asphalt’sspeed of construction allows plannersand managers a way to fix congestion hotspots and bottlenecks, quickly and cost-effectively—often, all the work can bedone at off-peak hours, so that the morn-ing and evening commutes go smoothly.Because a newly rehabilitated asphalt roadcan be opened for traffic as soon as ithas been compacted and cooled, keepinglanes coned off for curing is not necessary.

Driving on smooth roads also saves fuel.Studies at a Nevada test track showedthat vehicles driving on smooth roadsconsumed 4.5 percent less fuel, on average, than on rough pavement.4

Asphalt can make rough roads smoother,quickly, cost-effectively, and without prolonged road closures.

Urban heat island reduction: howasphalt pavements can helpThe urban heat island (UHI) effect—thephenomenon that makes cities 2 to 10°Fwarmer than nearby rural areas on a hotsummer day—is not a black and whiteissue. Many factors contribute to heatretention in urban areas. And, manystrategies for reducing the UHI effect arebeing explored.5

Because pavements cover a large percent-age of urban areas, and because improve-ments to pavements occur more frequent-ly than improvements to buildings, pave-ment-related strategies for cooling off thecity core are of interest.

Some attention has been given to the ideaof making pavements more reflective, onthe theory that a lighter-colored or morereflective surface may keep things cooler.But on closer look, it is seen that manyfactors other than color and reflectivity—including pavement thickness and thetype of surface used—can influence theway a pavement retains, radiates, and/or

ENERGY & RECYCLING PERFORMANCE WATER QUALITY

ASPHALTCLEAN AIR & COOL CITIES

The Sustainable Pavement

Clean Air & Cool Cities


Clean Air & Cool Citiesreleases heat. When and how heat isreleased is also of importance.

Porous asphalt pavements have beenshown to lower nighttime surface temper-atures as compared to other pavements.A thermal image taken by satellite(ASTER) over Phoenix in October 2003(Figure1) shows that an impervious freeway which has been resurfaced withopen-graded asphalt is actually cooler atnight than nearby freeways without theasphalt surface. Also influencing the cooling of pavements is the presence ofsound walls (which can trap heat), vegetation cover on the adjacent landscape, whether the pavements are ator below grade, and the thickness of thepavement itself. In the same ASTERimage, the hottest heat signature is at theairport, where the impervious runwaysare 23 inches thick.

REFERENCES

1. Gambatese, John A. and Sathyanarayanan Rajendran, “Sustainable Roadway Construction: Energy Consumption and Material Waste Generation ofRoadways,” American Society of Civil Engineers, Reston, VA. Proceedings of 2005 Construction Research Congress.(http://www.pubs.asce.org/WWWdisplay.cgi?0520020. Downloaded June 22, 2006.)

2. Report to Members 2001, National Asphalt Pavement Association, Lanham, MD. 2002.

3. Federal Register, February 12, 2002, pp. 6521 ff.(http://frwebgate.access.gpo.gov/cgi-bin/getpage.cgi?dbname=2002_register&position=all&page=6521, accessed September 7, 2006.) Also, Federal Register,November 8, 2002, pp. 68124 ff.(http://frwebgate.access.gpo.gov/cgi-bin/getpage.cgi?dbname=2002_register&position=all&page=68124, accessed September 7, 2006.)

4. Sime, M., et al. WesTrack Track Roughness, Fuel Consumption, and Maintenance Costs. Tech Brief published by Federal Highway Administration,Washington, DC. January 2000.

5. Golden, Jay, and Kamil Kaloush, “A Hot Night in the Big city: How to Mitigate the Urban Heat Island,” Public Works, December 2005.(http://www.pwmag.com/industry-news.asp?sectionID=770&articleID=268116, accessed September 5, 2006.)

Figure 1

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3/4 inchopen gradedasphalt over

imperviouspavement

Airport: impervious pavement

Interstate w/ impervious pavement

Highway w/ impervious pavement

Below gradew/ sound walls

Above gradew/ landscape

Below grade w/ sound walls

ENERGY & RECYCLING PERFORMANCE

ASPHALT


Better Water QualityPorous asphalt...• Conserves water• Allows for better use of land • Reduces runoff• Promotes infiltration• Cleans stormwater• Replenishes aquifers• Protects streams

Porous asphalt offers a powerfultool in the toolbox for storm-water management.In the natural environment, rainfall sinksinto soil, filters through it, and eventuallyfinds its way to streams, ponds, lakes,and underground aquifers. The builtenvironment, by way of contrast, seals thesurface. Rainwater and snowmelt becomerunoff which may contribute to flooding.Contaminants are washed from surfacesdirectly into waterways without undergo-ing the filtration that nature intended.1

For these reasons, managing stormwateris a significant issue in land use planningand development. Stormwater manage-ment tools can serve to mitigate theimpact of the built environment on natu-ral hydrology. Unfortunately, however,

they also can lead to unsound solutionssuch as cutting down stands of trees inorder to build detention ponds.

Porous asphalt pavements allow for landdevelopment plans that are more thought-ful, harmonious with natural processes,and sustainable. They conserve water,reduce runoff, promote infiltration whichcleanses stormwater, replenish aquifers,and protect streams.

A typical porous pavement has an open-graded surface over an underlying stonerecharge bed.2 The water drains throughthe porous asphalt and into the stonebed, then, slowly, infiltrates into the soil.If contaminants were on the surface at thetime of the storm, they are swept alongwith the rainfall through the stone bed.From there they infiltrate into the subbaseso that they are subjected to the naturalprocesses that cleanse water.

Construction and performancePorous asphalt pavements are fast andeasy to construct. With the proper infor-mation, most asphalt plants can easilyprepare the mix and general paving con-tractors can install it.

The stone bed, often eighteen to thirty-six inches in depth, provides a tremen-dous subbase for the pavement. As aresult, porous asphalt pavements tend notto exhibit cracking and pothole formationproblems. The surface wears well. Underthe stone bed is a geotextile which keepsfine particles from moving into the stonebed from below and filling in the spaces.

Porous asphalt has been proven to last fordecades, even in extreme climates, andeven in areas with many freeze-thawcycles.3

The underlying stone bed can also pro-vide stormwater management for adjacentimpervious areas such as roofs androads. To achieve this, stormwater is con-veyed directly into the stone bed, whereperforated pipes distribute the waterevenly.

EconomicsPorous pavement is a sound choice oneconomics alone. A porous asphalt pave-ment surface costs approximately thesame as conventional asphalt. Becauseporous pavement is designed to “fit into”the topography of a site, there is general-ly less earthwork. The underlying stonebed is usually more expensive than aconventional compacted sub-base, butthis cost difference is offset by eliminat-ing the detention basin and other compo-nents of stormwater management sys-tems. On projects where unit costs havebeen compared, the porous pavement hasbeen the less expensive option. Porouspavements are therefore attractive onboth environmental and economicgrounds.1

An installation at the University of NorthCarolina in Chapel Hill included parkinglots where some sections were construct-ed from porous asphalt and others usedporous concrete. The cost differential wasapproximately 4:1 – that is, the porousconcrete pavement cost four times asmuch as the porous asphalt pavement.1


CLEAN AIR & COOL CITIES


WATER QUALITY


Impact on groundwaterAsphalt pavements are compatible withclean water. Studies show that asphaltpavements and stockpiles of reclaimedasphalt pavement do not leach.4,5

Contaminants on the surface of pave-ments tend to become part of runoff, butwith a porous pavement, they are washedinto the stone bed. From there they flowdown into the soil, where beneficial bac-teria and other natural processes cleansethem. Data are limited, but indicate avery high removal rate for total suspend-ed solids, metals, and oil and grease.1

Figure 1 shows the effect of a porousasphalt pavement on the hydrology of adeveloped site.

Cooler citiesPorous asphalt pavements have beenshown to mitigate the urban heat islandeffect. Open-graded asphalt roads andhighways—which use the same surfacematerial as porous parking lots—havebeen shown to lower nighttime surfacetemperatures as compared to imperviouspavements. In at least one city, the hottestheat signature is at the airport, with itsthick, dense, impervious runways.6

Comparisons to other asphaltpavementsThe surface of a porous asphalt pavementwears well. While slightly coarser thansome pavements, it is attractive andacceptable. Most people driving or

walking on the pavement will not notice(or believe) that it is porous.

Like all asphalt pavements, porous pavements are ADA-friendly.

Environmental applicationsAsphalt pavements have been used formany years to enhance water quality. Atlandfills, asphalt liners and caps keepcontaminants from leaking into ground-water. Drinking water reservoirs linedwith asphalt pavement have been used inCalifornia since the 1950s. Salmon hatch-eries and fish rearing ponds in the PacificNorthwest use asphalt liners.7

Variations on the themePorous asphalt can be used successfullyin parking lots, walkways, and play-grounds. Several current suburban proj-ects are exploring its use in subdivisionroads. A few porous highways and citystreets have been constructed, both in theU.S. and in Europe, and have performedwell.

The open-graded asphalt surface used forporous pavements has been used exten-sively to surface high-volume highwaysthat carry heavy trucks. Its benefitsinclude noise reduction, a decrease insplash and spray kicked up by vehicles inheavy downpours, and mitigation of theurban heat island effect.

Better Water Quality

REFERENCES1. Cahill, Thomas H., et al., “Porous Asphalt: The Right Choice for PorousPavements,” Hot Mix Asphalt Technology, National Asphalt Pavement Association,Lanham, MD, September/October 2003.

2. Jackson, Newt, Design, Construction and Maintenance Guide for Porous AsphaltPavements (IS-131), National Asphalt Pavement Association, Lanham, MD, 2003.

3. MacDonald, Chuck, “Porous Pavements Working in Northern Climates,” Hot MixAsphalt Technology, National Asphalt Pavement Association, Lanham, MD,July/August 2006.

4. Kriech, AJ, et. al. “Determination of polycyclic aromatic compounds in asphalt andin corresponding leachate water.” Polycyclic Aromatic Compounds, Taylor & FrancisGroup, Philadelphia, PA. Volume 22, Numbers 3-4, pp. 517-535. 2002.

5. Townsend, Timothy, and Allen Brantley. Leaching Characteristics of Asphalt RoadWaste. University of Florida, 1998.(http://www.hinkleycenter.com/publications/townsend_98-2.pdf, accessed September1, 2006)

6. Golden, Jay, and Kamil Kaloush, “A Hot Night in the Big City: How to Mitigate theUrban Heat Island,” Public Works, December 2005. (http://www.pwmag.com/indus-try-news.asp?sectionID=770&articleID=268116, accessed September 5, 2006)

7. Environmental Applications for Hot Mix Asphalt (PR-1). Asphalt Institute,Lexington, KY. Undated.

Figure 1: Hydrograph comparison showing how porous pavement reduces peak flow andtotal volume of runoff

Source: Cahill Associates

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decreased stormwater dischargewith porous pavement

ENERGY & RECYCLING PERFORMANCE WATER QUALITY

ASPHALT


Recycling & Energy Reduction


CLEAN AIR & COOL CITIES


Asphalt pavementsare America’s most recycled productAccording to the U.S.

Environmental Protection Agency and theFederal Highway Administration, about90 million tons of asphalt pavement isreclaimed each year, and over 80 percentof that total is recycled.1

Reclaimed asphalt pavement (RAP) canbe recycled into pavement that is as high,or even higher, in quality as pavementsmade of all-virgin materials. And, thesame material can be recycled again andagain; it never loses its value. The asphaltcement—the glue that holds the pavementtogether—retains its ability to function asglue or cement, so that it is reused for itsoriginal purpose. The aggregates (rocks,sand and gravel) in the original pavementare also conserved. Many pavements thatare more than 20 years old are actuallyworth more than they were when origi-nally constructed.

It is estimated that recycling of asphaltpavements saves the American taxpayer$1.8 billion per year. It also saves hundreds of acres of landfill space each year.

Materials from other industries are rou-tinely recycled into asphalt pavementsinstead of going into landfills. Some ofthe most common are rubber from usedtires, glass, asphalt roofing shingles, andblast furnace slag.

Asphalt plants also recycle the fine miner-al particles that are generated in theprocess of producing asphalt pavementmaterial. This routine recycling of co-gen-erated material helps to conserve naturalresources.

Less energy consumed in building pavementsAsphalt pavements require about 20 per-cent less energy to produce and constructthan other pavements.2

Rubblization of concrete pavement withan asphalt overlay also saves energy. Therubblized pavement does not need to behauled away; new base material does notneed to be trucked in; and landfill spaceis saved. In addition, the need for mining,crushing, and processing of virgin materi-als is reduced.3


Recycling & Energy Reduction Less energy consumed by thetraveling public Reducing congestion—which wastes fuel—by constructing asphalt pavements justmakes sense. Asphalt pavements arefaster to construct and rehabilitate.

Asphalt pavement rehabilitation can beaccomplished during off-peak hours. Onhighly traveled routes, much of this workcan be done at night. One or more lanescan be closed after the evening rush hour,milled for recycling, resurfaced, and then

opened for traffic the following morning.Most motorists do not have to deal withthe inconvenience of construction delay.

Because a new or newly rehabilitatedasphalt pavement can be opened to trafficas soon as it has been compacted andcooled, there is no question of waiting fordays or weeks, with traffic being detouredor squeezed into fewer lanes, for thematerial to cure.

REFERENCES

1. A Study of the Use of Recycled Paving Material: Report to Congress, June 1993, Federal Highway Administration and United States EnvironmentalProtection Agency, Washington, DC. FHWA-RD-93-147 and EPA/600/R-93/095.

2. Gambatese, John A. and Sathyanarayanan Rajendran, “Sustainable Roadway Construction: Energy Consumption and Material Waste Generation ofRoadways,” American Society of Civil Engineers, Reston, VA. Proceedings of 2005 Construction Research Congress.(http://www.pubs.asce.org/WWWdisplay.cgi?0520020. Downloaded June 22, 2006.)

3. Decker, Dale, Rubblization: Design and Construction Guidelines on Rubblizing and Overlaying PCC Pavements with Hot-Mix Asphalt (IS-132). NationalAsphalt Pavement Association, Lanham, MD. 2006.

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Performance Means Sustainability

ENERGY & RECYCLING PERFORMANCE WATER QUALITY CLEAN AIR & COOL CITIES

ASPHALT



Roads that don’t wear outOne of the keys to sustainability is long life.With Perpetual Pavements, asphalt pave-ments have an extremely long lifespan.1

A Perpetual Pavement is constructed so thatdistress occurs in the top layer only. Theonly rehabilitation required is removal of thesurface and resurfacing with an asphaltoverlay. Using current pavement technolo-gies, this can be done on an infrequentbasis—every 15 to 20 years. The reclaimedmaterial is then recycled. Perpetual Pavementis the ultimate in sustainable design andconstruction.

While the Perpetual Pavement name is rela-tively new, the concept is not. In fact, morethan 35 pavements have received thePerpetual Pavement Award since 2001.These award-winning roads, streets, high-ways, and airport runways have been inplace for at least 35 years, with a minimumof maintenance and no full-depth recon-struction.

RubblizationWhen concrete pavements reach the end oftheir useful life, they must undergo expen-sive, time-consuming rehabilitation. Thisprocess squanders precious naturalresources, in addition to inconveniencingthe traveling public. Prolonged road closuresalso lead to congestion, which consumesenergy and produces excess emissions.Asphalt’s answer is a sustainable processcalled rubblization, in which the concretepavement is left in place, rubblized (frac-

tured), and used as the base for a newPerpetual Pavement.

In addition to the environmental advantages,cost savings can be significant. The rub-blization process is much faster than theremove-and-replace option. It can also beaccomplished through temporary lane clo-sures, without the necessity for traffic to bedetoured onto parallel routes.

Public safetySmooth asphalt roads give vehicle tiressuperior contact with the road.

One type of asphalt surface, known asopen-graded friction course, allows rainwater

to drain through the surface layer and off tothe sides, reducing the amount of splashand spray kicked up by vehicles.

Noise reductionAsphalt is the quiet pavement. Quiet pave-ment technologies include open-graded sur-faces, fine-graded surfaces, and two-layeropen-graded pavements.2 Studies show thatthe noise-reducing properties of asphalt lastfor many years.3

Noise reductions of 3 to 10 dB(a) are com-mon. Reducing noise by 3 dB(a) is about thesame as doubling the distance from the roadto the listener, or reducing traffic volume by50 percent.

For more information on quiet pavementtechnology, visit www.quietpavement.com.

Congestion reductionAsphalt pavements are faster to constructand rehabilitate. In crowded urban areas,where closing a road for rehabilitation orreconstruction would dump increased trafficon neighboring routes—adding to conges-tion—asphalt is the answer. Highways androads can be milled for recycling, then over-laid, during off-peak hours, so that mostmotorists are never inconvenienced.

Smoothness and conservationStudies at a pavement test track in Nevadahave shown that driving on smoother sur-faces can reduce fuel consumption in theneighborhood of 4.5 percent.4

When trucks are driven on rough surfaces,the tires bounce and deliver heavy,


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Performance Means Sustainabilitypunishing impacts to the pavement. Someexperts estimate that a 25 percent increasein smoothness can result in a 9 to 10 per-cent increase in the life of pavements.

Building smooth asphalt roads is simple andcost effective. Keeping them that way is fast,easy and inexpensive.

Taking the punishmentAny doubts about whether asphalt isdurable can be answered at racetracks andairports. These pavements are punished byheavy loads, but asphalt stands up to them.

When vehicles reach speeds of 200 mphand more, and a car’s undercarriage clearsthe pavement by about one inch, the pave-ment had better be smooth. That’s whynearly all racetracks—for both Formula Oneand NASCAR racing—use asphalt.

REFERENCES

1. Perpetual Bituminous Pavements. Transportation Research Circular Number 503. Transportation Research Board, Washington, DC. December 2001.

2. Newcomb, Dave, and Larry Scofield, “Quiet Pavements Raise the Roof in Europe,” Hot Mix Asphalt Technology, National Asphalt Pavement Association,Lanham, MD, September/October 2004.

3. Reyff, James, et al., I-80 Davis OGAC Pavement Noise Study: Traffic Noise Levels Associated With an Open Grade Asphalt Concrete Overlay. Prepared forCalifornia Department of Transportation by Illingworth & Rodkin, Inc., Sacramento, CA, December 1, 2002.

4. Sime, M., et al. WesTrack Track Roughness, Fuel Consumption, and Maintenance Costs. Tech Brief published by Federal Highway Administration,Washington, DC. January 2000.

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The Sustainable Pavement - Asphalt Pavement … safety Smooth asphalt roads give vehicle tires...

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