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LSustainable Asphalt, Now and Tomorrow

Long before “sustainability” became an eagerly pur-sued part of the American business plan, the asphaltindustry initiated research and field practices thathave constantly enhanced the viability of asphalt asan environmentally sound building material.

To date, the monumental accomplishment ofthis initiative lies in recycling. Asphalt is the mostrecycled material in America. About 100 milliontons of old pavement are reclaimed every year, withabout 60 million tons reused in new asphalt mixes,and some 40 million used in other pavement-relat-ed applications, such as aggregate road base.1

Asphalt pavement is unique not only in thevolume recycled, but also its renewability. It is com-prised of approximately 95 percent aggregates(stone, sand and gravel) and about 5 percentasphalt cement. When asphalt pavement is reusedin a new asphalt mix, the old asphalt cement isrejuvenated so that it becomes an active part of theglue that holds the new pavement together, just likethe old aggregate becomes part of the aggregatecontent of the new mix. These singular propertiesmake asphalt a uniquely renewable pavement.

Powering the trend to recycling/reusing asphaltis economics. Decades of research and engineeringhave improved the cost efficiency of converting oldasphalt into a reusable resource that has tangiblevalue. Today, pavement engineers, governmentagencies and contractors regard old asphalt as anasset, not waste, and the trend to recycling andreuse continues to gain momentum as a result.

The industry has worked on other technologiesthat reduce air emissions including greenhousegases and other contributors to climate change.These technologies include warm-mix asphalt,

with lower emissions due to reduced temperatures,and long life pavements which reduce greenhousegas emissions by reducing the frequency of repairand replacement.

And modern asphalt technology has deliveredasphalt pavement designs that actually enhance thequality of stormwater runoff even as they improvedriving safety by reducing the amount of spray pro-duced by vehicle tires.

Past, current and future advancements inasphalt as an environmentally sustainable pavingmaterial are especially important because asphalt issuch a primary component of America’s transporta-tion system and because the quantities of materialused annually are so large.

Of the 2.6 million miles of paved roads in theUnited States, over 94 percent are surfaced withasphalt. Approximately 85 percent of the nation’sairfield pavements and 85 percent of the parkinglots are also surfaced with asphalt. There are about4,000 asphalt mixing plants located in the UnitedStates and the industry employs, directly or indi-rectly, 300,000 U.S. workers. Because of the vastextent of use of this material, even small changes inasphalt pavement technology can make a big differ-ence in terms of greenhouse gas emissions.

2 The Road Ahead

3 Converting to Warm-Mix Asphalt

4 Doubling the Use of Reclaimed Materialsin Asphalt Pavements

5 Expanding Implementation of Perpetual Pavement

7 Accelerating Appropriate Use of Porousand Open-graded Pavements

8 Conclusion

9 References

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None of the advancements in asphalt tech-nology would have been possible without avibrant research and technology deploy-

ment program. Leading the asphalt research effortis the National Center for Asphalt Technology(NCAT) in Auburn, Alabama, which originally wasendowed by industry and today is directed by apublic-private partnership. With its 1.7-mile pave-ment test track and its 40,000-square-foot researchfacility, NCAT conducts a productive, $5 millionper year research program that focuses on innova-tions that directly affect and improve the roads wedrive on every day.

An important aspect of the industry’s researchprogram is that it is based on partnering. Partnersin current and past initiatives include the NationalAsphalt Pavement Association (NAPA), the FederalHighway Administration (FHWA), the FederalAviation Administration (FAA), the AmericanAssociation of State Highway and TransportationOfficials (AASHTO), the state Departments ofTransportation (DOTs), the TransportationResearch Board (TRB), the U.S. Army Corps ofEngineers, the Environmental Protection Agency(EPA), related industry associations, theOccupational Safety and Health Administration(OSHA), the National Institute for OccupationalSafety and Health (NIOSH), and the labor unions.There is also a broad range of international partnerswith whom the industry shares knowledge, conductsjoint research, and cooperates on industry matters.

One of the first breakthroughs in asphalt pave-ment technology achieved by this partnership wasSuperpave, a pavement design system that hasenhanced pavement performance and durability inmany ways. It was developed with federal fundingunder the Strategic Highway Research Program

(SHRP) in the late 1980s and early 1990s.Superpave has become so widely accepted that useof the term is actually disappearing – what used tobe called the Superpave design system is now thenorm for designing asphalt pavements in much ofthe U.S.

Another example of partnering was the initia-tive that began in the late 1980s in which NAPAworked with EPA on research into air emissions,including greenhouse gases from asphalt plants.The studies showed that emissions from asphaltplants are low and well controlled; they resulted inEPA declaring that asphalt plants are not majorsources of hazardous air pollutants.2

Nonetheless, the industry continued to work toreduce emissions. In fact, total emissions fromasphalt operations decreased by 97 percent from1970 to 1999, while production of asphalt pave-ment material increased by 250 percent.3 Theindustry is proud of its record of environmentalstewardship and its proactive position of continu-ously reducing emissions, including greenhouse gasemissions.

As impressive as our gains have been in recentyears, we can still achieve significant gains inaddressing climate change in the coming years byaccelerating research and deployment of technolo-gies that reduce greenhouse gas emissions. We canincrease use of warm-mix asphalt to represent themajority of all the pavement material produced inthe U.S.; we can double the reuse/recycling ofasphalt pavements; we can make PerpetualPavements the standard design method; and we canhave porous pavements accepted as a best manage-ment practice for reducing stormwater runoff andimproving water quality. More information aboutthese strategies follows.

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Warm-mix technologies allow for produc-tion and placement of asphalt pavementmaterial at lower temperatures than con-

ventional hot mix technologies. Conventionalasphalt pavement material is produced at around320o F and warm mix is typically produced at tem-peratures ranging from 280o F down to 212o F.4

The potential for warm mix has won broad supportamong road managers and contractors. In five yearsfollowing the first public demonstration of warmmix in the U.S. in 2004, scores of warm mix proj-ects have been constructed in 40 states.

Warm mix was originally explored for its envi-ronmental benefits, which include reduced fossilfuel consumption and reduced emissions, includinggreenhouse gas emissions. Contractors and agencieshave also discovered numerous construction andperformance benefits, including the potential toextend the paving season in northern climates, thepotential to store pavement mix for longer periods,a longer window of opportunity for compactingpavement, and increases in recycling rates.

Running warm mix can reduce energy con-sumption during the manufacturing of the asphaltpavement mixture by an average of 20 percent,which decreases total life-cycle greenhouse gas emis-sions by 5 percent. In terms of greenhouse gasemissions, this equates to cutting 1 million tons ofcarbon dioxide emissions annually. Combiningwarm mix with reuse/recycling yields even greaterbenefits. Warm mix with 25 percent reclaimedasphalt pavement could potentially offset asphalt

pavement life-cycle greenhouse gas emissions by 15to 20 percent. The potential for total savings ingreenhouse gas emissions using both warm mix andrecycling is about 3 million tons per year.

NAPA, FHWA, AASHTO, and researchers cre-ated a Technical Working Group whose purpose isto evaluate warm-mix technology performance,quantify environmental benefits, develop perform-ance specifications, provide technical guidance, anddisseminate information. The partnering approachhas been of immense support to efforts to deploywarm mix.

So far, implementation has proceeded with vir-tually no complications.5, 6, 7, 8, 9, 10 Demonstrationprojects, trials, and test projects have included thefull variety of asphalt mixture types. At least 10states have adopted permissive specifications, clear-ing the way for contractors to produce and placethe mix at low temperature as long as it meets allother criteria.

Experience with applied research and technolo-gy development suggests that warm mix may makeit possible to increase the rates of reuse/recyclingeven more. Applied research on this topic will behelpful in speeding the rate of acceptance of com-bining the two technologies.

Another opportunity for applied research is fulldocumentation of emission reductions, with specif-ic focus on greenhouse gas emissions. Such researchwould also assist agencies in taking full advantageof warm mix to meet air quality guidelines.

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04

The use of reclaimed asphalt pavement (RAP)has been widespread for about 30 years.11

Asphalt pavement is America’s most recycledmaterial. Every year, more than 100 million tons ofasphalt pavement material is reclaimed and virtuallyall of it is reused or recycled into new pavements.Materials from other industries, including roofingshingles and ground rubber from used tires, canalso be beneficially incorporated into asphalt pave-ments. The key to this is sound engineering,design, and technology.

Increased use of RAP as a percentage of thetotal asphalt mix can significantly reduce green-house gas emissions by eliminating the significantfuel consumption required to acquire and processraw materials for virgin mix. Currently, RAP makesup 12 percent of the average asphalt mix by vol-ume, with the remainder comprised of virgin aggre-gate and asphalt cement.

Contributing to this average are states that rou-tinely use 30 percent RAP and states that permitminimal use. If we increase RAP usage to 25 per-cent of the average mix, we will reduce total life-cycle greenhouse gas emissions by 10 percent,which equates to 2 million tons offset annually.

One of the unique qualities of asphalt cement isthat it is rejuvenated when RAP is incorporated intonew pavement, becoming an integral part of thebinder. This is referred to as the highest and best use.

In view of the high reuse/recycling rate in leadstates, including a preponderance of evidence thatthe quality of asphalt pavements incorporating RAPis equal to or better than pavements using all virginmaterials, there is ample opportunity to double thequantity of RAP used within five years.

Part of the challenge is to encourage agencies inrural areas to allow milling on pavements prior tothe placement of asphalt overlays. This will providemore material for recycling in areas where RAP is

scarce, and it will improve the performance of therehabilitated pavement by removing distresses fromthe existing surface.

FHWA has organized the RAP Expert TaskGroup (ETG), which brings together stakeholdersfrom government, industry, and academia to investi-gate obstacles to increasing RAP use. As part of thismission, the ETG has identified states with particu-larly high and particularly low levels of reuse/recy-cling. The ETG is also charged with achieving thedesired increases through technology transfer/accel-erated deployment strategies, and eliminating artifi-cial and arbitrary barriers to increased recycling infavor of performance-based pavement criteria.

There are also opportunities for applied research,including quantifying the environmental benefits ofincreased RAP use, developing technologies and pro-cedures to recycle high percentages of reclaimedmaterial, developing technologies and procedures tobetter preserve the aggregate gradation in RAP, andimproving performance testing methods and specifi-cations for use of RAP and roofing shingle mixtures.All these activities would contribute to increasing theoverall rate of recycling and therefore provide reduc-tions in emissions of greenhouse gases.12

Economic SustainabilityReuse/recycling is not only an environmentally

sustainable practice, it is an economically sustain-able one. NAPA estimates that we have 18 billiontons of asphalt pavement already in place onAmerica’s roads and highways. Because of the abili-ty to reuse and recycle this material indefinitely, ourhighways are a resource for future generations. Notonly are our roads a primary engine of the econo-my, they have a high residual value as a source ofconstruction materials. As a note, the process ofreclaiming and processing these materials has a verylow environmental impact.

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B L A C K A N D

09 GREENB L A C K A N D 05

Perpetual Pavement is the name given to anasphalt pavement that is designed not to fail.Construction is in layers whose properties serve

a combination of different functions; they all add upto an extraordinarily long-lasting pavement. Surfacedistresses may occur eventually, but they do not pen-etrate deep into the pavement’s structure. Routinemaintenance involves infrequent milling of the toplayer for recycling, then placing a smooth, quiet,durable, safe new overlay. A Perpetual Pavementnever needs to be completely removed and replaced.In the world of pavements, this is the ultimate ineconomic and environmental sustainability.

Perpetual Pavements can mitigate climatechange by reducing greenhouse gas emissions, bothnow and for generations to come. PerpetualPavements reduce greenhouse gas production inseveral ways.

� Since only the surface is renewed, the basestructure stays in place, thereby significantlyreducing greenhouse gases associated with vir-gin raw materials acquisition and placement.

� Greenhouse gas emissions associated withcomplete removal and replacement of pave-ments that have reached the end of their usefullife is avoided.

� Greenhouse gas emissions associated withconstruction delays are greatly reduced becausemaintenance and rehabilitation can be donequickly in off-peak hours, unlike the remove-and-replace option, which necessitates 24-hourroad closures. Limiting closures to off-peakhours can reduce delays for road users by atleast a factor of 12, i.e., a 2 1/2-minute delayversus a 30-minute delay.

Perpetual Pavements are more cost-effectivethan traditional asphalt pavements while enhancingdurability, performance, and long life. Reuse/recy-cling is part of the maintenance and rehabilitationprocess.13 All these factors conserve constructionmaterials and reduce greenhouse gases.

Once the road is constructed, it becomes a per-manent asset within the transportation infrastruc-ture system. A Perpetual Pavement does notbecome a reconstruction problem for future genera-tions.

Perpetual Pavements can also keep roadssmoother. Significant fuel savings are associatedwith smooth pavements. It has been documentedunder tightly controlled conditions that driving aheavily loaded truck on a smooth road consumesabout 4.5 percent less diesel than driving on arough one.14

The history of Perpetual Pavements goes backto the 1960s, although the term was not used untilaround 2000. Full-depth asphalt pavements firstachieved wide acceptance in the 1960s as a way ofminimizing materials use and construction costs.11

At that time, it was assumed that the design wouldresult in a “20-year design life,” but experience hasshown that such pavements have lasted for over 40years with no sign of structural failure. Engineeringstudies in the states of Kansas,15 Minnesota,16

Ohio,17 Oregon,18 and Washington18 have validatedthese observations.

Beginning in 1999 and 2000, asphalt pave-ment researchers initiated efforts to understand theengineering features and performance characteris-tics of Perpetual Pavements. Research has been con-ducted at NCAT, the Asphalt Institute, theUniversity of California at Berkeley, the University

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09 GREENB L A C K A N D 06

of Illinois, and other leading institutions in theU.S. and around the world. The research has led tothe development of materials, design methods, andperformance criteria to enable agencies to designpavements that ensure long life without wastingmaterials due to overdesign.

There are already many pavements around theUnited States that fit the Perpetual Pavement defi-nition. In recognition of that fact, in 2001 theasphalt industry created a program to identifyPerpetual Pavements and honor the agencies thathave designed and maintained them. Fifty-ninePerpetual Pavement Awards have been presentedthrough 2008.

In addition to working toward the full integra-tion of Perpetual Pavement technologies into pave-ment design guides, the asphalt industry will con-tinue to pursue research to advance PerpetualPavement best practices.

There are currently two national studies onPerpetual Pavement through the NationalCooperative Highway Research Program (NCHRP)

focused on the engineering characteristics that willbe critical to the design of long-life pavements.Pavements have been constructed with instrumentsembedded in the various layers to ascertain theirresponses to truck loadings at a variety of locations.These include the NCAT Pavement Test Track andthe Minnesota Road Research Project, as well as inhighways located in Kansas, Ohio, Pennsylvania,Wisconsin, and other states. These will provide cru-cial information on the field behavior of PerpetualPavements.

Significant opportunities for applied researchon Perpetual Pavements include an investigation ofhigh-stiffness base materials, which have the poten-tial to reduce both costs and greenhouse gas emis-sions, and research on the impact of these long-lifepavements on climate change, specifically green-house gases.

In summary, Perpetual Pavements conserve natural resources, reduce life-cycle costs, save fuel,and reduce fuel consumption and greenhouse gasemissions.

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Porous and open-graded asphalt pavementshave been shown to have a dramatic beneficialeffect on water quality. These pavements have

been used widely for over 30 years with an excellentrecord of success. Open-graded pavement is madewith same-size rocks, creating a web of interlockingpores that allow water to flow through the surface.19

Open-graded pavements are used mainly in twotypes of applications. First, open-graded frictioncourses are widely used for surfacing roads and high-ways. The pavement layer directly beneath this isimpermeable. During a rainstorm, instead of pool-ing on the surface or bouncing off it, rain drainsthrough the surface and out to the sides. Splash andspray are greatly reduced, enhancing safety.

Second, porous pavement systems are stormwa-ter management tools with an open-graded surfaceover a stone recharge bed. The system is designedand constructed to collect stormwater, which theninfiltrates into the ground. Porous pavement sys-tems are used mostly for parking lots, but they havealso been used successfully for roads in communi-ties like Pringle Creek in Salem, Oregon.20

Both applications can be used to improve waterquality. Porous asphalt surfaces allow roads andhighways to function as linear stormwater manage-ment systems. Porous parking lots store stormwater,reduce runoff, promote infiltration and groundwa-ter recharge, allow evaporative cooling of theatmosphere, diminish erosion on stream banks,reduce particulates in stream water after storms,and improve water quality.21

Porous asphalt pavements are accessible andaffordable. They can be produced and constructedby any qualified contractor. Open-graded highwaysurfaces have additional environmental and safetybenefits. They reduce road noise significantly.22, 23, 24,

25, 26 Texas DOT reported that replacing a conven-tional surface with open-graded friction course in ahigh-accident area reduced wet-weather accidentsby 93 percent and reduced fatalities by 86 percent.27

With respect to porous pavement systems forstormwater management, some local authoritiesmay allow the construction of porous pavementsystems but still require total redundancy with theuse of conventional stormwater management struc-tures. Applied research documenting the effective-ness of porous pavements, together with a programof continuing education, could be helpful inexpanding the use of these pavements and avoidingusing them inappropriately.

The industry and partners will use appliedresearch, demonstration projects, open houses,Web-based tools, and other continuing educationefforts to accelerate the deployment of porousasphalt solutions in the months and years to come.Industry will also assist federal and state agencies indeveloping design guidance for porous asphaltapplications. And we will look for opportunities todocument the environmental effectiveness and costbenefits of porous asphalt pavement, improve mate-rials and mix designs, and evaluate highways as lin-ear stormwater management systems.

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09 GREENB L A C K A N D 08

The engineers, scientists, contractors andmanagers who guide the development ofasphalt pavement have made it one of the

most environmentally advanced building materialsin the world by constantly improving its cost effec-tiveness and safety.

By extending pavement life – by improvingmaterials, designs, or best practices – these profes-sionals reduce the cost to the environment and tothe taxpayer. By improving the desirability ofreclaimed asphalt in new mixes, they have reducedthe cost of the mix and the demand for virginasphalt cement and virgin aggregates.

Going forward, the industry and its partnerswill pursue the same mandate. It is not enough thatthe asphalt industry is capable of cutting green-house gas emissions or reducing energy usage orenhancing the quality of stormwater runoff.Solutions must also make sense economically forthe agencies and companies that buy them.

Going forward, there will be more research, notless. As we conceive and prove new warm-mix tech-nologies, more pavement managers will use warmmix in more applications. As we document the long

life and long-term cost effectiveness of PerpetualPavement, more engineers will adopt this designsystem for high-load, high-volume roads. As we testand verify new mix dynamics for porous asphalt,road managers will find more ways to use it.

That is how we will make warm-mix asphaltthe primary pavement material – and reduce energyconsumption and greenhouse gas emissions in theprocess. That is how we will double the reuse/ recy-cling of asphalt pavements – and reduce energyconsumption, emissions, and the use of virgin nat-ural resources. That is how we will make PerpetualPavements the standard design method for road-ways – and completely redefine the life-cycle expec-tations and economics of highways in America.And that is how we will make porous pavementsaccepted as a best management practice for reduc-ing stormwater runoff and improving water quality.

In responding to these challenges, the asphaltpavement industry and its partners will continue toimprove the environmental performance of asphalt,already one of the most sustainable pavement mate-rials on earth.

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1. Hansen, K., and D. Newcomb, RAP Usage Survey,National Asphalt Pavement Association, Lanham,Maryland, August 2007.

2. 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 March 26, 2009.) 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 March 26, 2009.)

3. Cervarich, M., Report to Members 2001, NationalAsphalt Pavement Association, Lanham, Maryland,2002.

4. Prowell, B. D., and G. C. Hurley, Warm-Mix Asphalt:Best Practices. Quality Improvement Series 125,National Asphalt Pavement Association, Lanham,Maryland, 2008.

5. Prowell, B. D., G. C. Hurley and E. Crews, FieldPerformance of Warm Mix Asphalt at the NCAT TestTrack. Transportation Research Record 1998Transportation Research Board, Pp 96-102.Washington, D.C., 2007.

6. Acott, M., Warm-Mix Asphalt in the U.S.A., State ofthe Practice. Eurasphalt and Eurobitume 4thCongress, Copenhagen, Denmark, 2008.

7. D’Angelo, J., E. Harm, J. Bartoszek, G. Baumgardner,M. Corrigan, J. Cowsert, T. Harman, M. Jamshidi,W. Jones, D. Newcomb, B. D. Prowell (ReportFacilitator), R. Sines, and B. Yeaton, Warm-MixAsphalt: European Practice. International TechnologyScanning Program, Federal Highway Administration,February 2008.

8. Davidson, J., “Evotherm® Trial – Ramara Township,”McAsphalt Industries Limited, December 12, 2005.

9. Harder, G., Y. LeGoff, A. Loustau, Y. Martineau, andB. Heritier, “Energy and Environmental Gains ofWarm and Half-Warm Mix: Quantitative Approach.”Transportation Research Board 87th Annual Meeting,Washington, D.C., CD-ROM, 2008.

10. MacDonald, C., Warm-Mix Asphalt: Contractors’Experiences. Information Series 134, NationalAsphalt Pavement Association, Lanham, Maryland,2008.

11. McNichol, D., Paving the Way: Asphalt in America.National Asphalt Pavement Association, Lanham,Maryland, 2005.

12. Federal Highway Administration, AmericanAssociation of State Highway and TransportationOfficials, Asphalt Institute, National AsphaltPavement Association, and National Stone, Sand,and Gravel Association. National Asphalt Roadmap– A Commitment to the Future. NAPA SpecialReport 194, Lanham, Maryland, 2007.

13. Perpetual Bituminous Pavements, 2001.Transportation Research Circular 503,Transportation Research Board, Washington, D.C.

14. Sime, M., et al., WesTrack Track Roughness, FuelConsumption, and Maintenance Costs. Tech Brief,Federal Highway Administration, Washington,D.C., January 2000.

15. Cross, S. and R. Parsons, Evaluation of Expenditureson Rural Interstate Pavements in Kansas, KansasUniversity Transportation Center, University ofKansas, Lawrence, Kansas, February, 2002.

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16. Lukanen, E., Performance History of HMAPavements with Aggregate Base and PortlandCement Concrete Pavements, Minnesota AsphaltPavement Association, New Brighton, Minnesota,2002.

17. Gibboney, W., Flexible and Rigid Pavement Costson the Ohio Interstate Highway System, Westerville,Ohio, 1995.

18. Transportation Research Board, Pavement LessonsLearned from the AASHTO Road Test andPerformance of the Interstate Highway System,Transportation Research Circular E-C118,Washington, D.C., July 2007.

19. Hansen, K. Porous Asphalt Pavements forStormwater Management, Information Series 131,National Asphalt Pavement Association, 2008.

20. Estes, T. Green Paving Grows Beyond Parking Lots.Better Roads Magazine, Des Plaines, Illinois,October 2007.

21. University of New Hampshire Stormwater Center.(2007). University of New Hampshire StormwaterCenter 2007 Annual Report. Durham, NewHampshire: UNH Stormwater Center.

22. Hansen, D.I., R.S. James, and B. Waller, KansasTire/Pavement Noise Study, Asphalt PavementAlliance, Lanham, Maryland, June 2005.

23. Hansen, D.I., R.S. James, and B. Waller, OklahomaTire/Pavement Noise Study, Asphalt PavementAlliance, Lanham, Maryland, January 2005.

24. Hansen, D.I., R. S. James, and B. Waller,Tire/Pavement Noise Study for Arkansas APA,Asphalt Pavement Alliance, Lanham, Maryland,January 2005.

25. Newcomb, D., and L. Scofield, Quiet PavementsRaise the Roof in Europe, HMAT Magazine,National Asphalt Pavement Association, Lanham,Maryland, September/October 2004.

26. Reyff, J., et al., I-80 Davis OGAC Pavement NoiseStudy: Traffic Noise Levels Associated With anOpen Grade Asphalt Concrete Overlay. Prepared forCalifornia Department of Transportation byIllingworth & Rodkin, Inc., Sacramento, CA,December 1, 2002.

27. Rand, D. PFC Mixes Can Reduce Wet WeatherAccidents, HMAT Magazine, National AsphaltPavement Association, Lanham, Maryland,January/February 2007.

28. Barrett, M. E., & Shaw, C. B. (2007). StormwaterQuality Benefits of a Porous Asphalt Overlay.Transportation Research Record: Journal of theTransportation Research Board.

SUSTAINABLE ASPHALT, NOW AND TOMORROW