How the Road Influences Vehicle Fuel Economy

Almost 75 percent of the oil consumed in the United States is used as vehicle fuel.1 Despite increases in vehicle fuel economy over the past few decades, fuel costs remain a significant budget item for the public and businesses alike. Numerous factors influence the fuel economy of a vehicle from its aerodynamic properties, engine, tire pressure, and air temperature; however, just three basic forces impact fuel economy: vehicle internal friction, air drag, and rolling resistance. While these three forces always affect fuel economy, they vary in importance based on the vehicle speed.2 For example, when a vehicle is traveling at 30 miles per hour, 45 percent of the energy needed to move the car is used to overcome rolling resistance, but at 70 miles per hour, the rolling resistance only comprises about 20 percent of the energy requirement.

 

eff1

eff2

Vehicle Energy Consumption by Speed2

The rolling resistance forces a vehicle must overcome to maintain speed are linked to its suspension system, bearings, transmission, and, in part, the properties of the pavement. Three pavement properties are commonly understood to influence rolling resistance:

  1. Surface texture — how rough the mixture is;
  2. Smoothness — how rough the road feels to a driver; and
  3. Pavement stiffness —how much the surface of the pavement compresses underneath a vehicle).3

Pavement surface texture influences fuel economy through the interaction of the tire and the contacted area of the pavement. As a tire deforms, energy is converted into heat, which is lost to the rest of the tire and the atmosphere. Higher texture leads to additional fuel consumption.4,5,6,7 While it is important to consider the relationship between texture and fuel consumption, one must remember that pavement texture is key to ensuring safe driving conditions, particularly on wet roadways.

Numerous field and modeling efforts have been undertaken to understand the effect of pavement stiffness on fuel economy. Some theorists suggest that when tires and pavements interact, the pavement compresses causing the tire to continually drive “uphill.”8 Despite efforts, research has provided conflicting results as to the importance of pavement stiffness of fuel economy. Some studies based on modeling and measured results have shown there is no practical difference,9,10,11,12 while others have shown the differences could range from small to significant.13,14,15 An honest evaluation of current knowledge shows that researchers and engineers are still struggling to quantify the true impact of pavement stiffness on fuel economy.

What science has consistently shown is that pavement smoothness always has an impact of vehicle fuel consumption. The smoother the road, the less fuel the vehicle consumes.16,17,18 Smoothness influences the fuel consumption. As a vehicle travels along a roadway, energy is lost by the shock absorbers, suspension, and tires as these devices try to make the ride more comfortable for drivers and passengers. If a vehicle bounces less, the energy lost through this action is minimized.

According to FHWA, “Roughness as measured by IRI generally has the greatest effect on fuel economy for typical ranges of IRI on U.S. highway networks.”19 The best way to provide the driving public with the greatest possible fuel economy from the pavement infrastructure is to design and maintain smooth roadway networks. In addition to aiding the driving public, smoother pavements increase pavement longevity and require less maintenance than rougher roads.20 For more details, a recent literature review by the National Center for Asphalt Technology outlines the current state of knowledge surrounding pavement–vehicle interactions, as well as current limitations based on the available studies.21

  1. EIA (2012). Annual Energy Review 2011. DOE/EIA-384(2011). U.S. Energy Information Administration. Washington, DC.
  2. Beuving, E., T. De Jonghe, D. Goos, T. Lindahl, & A. Stawiarski (2004). Environmental Impacts and Fuel Efficiency of Road Pavements. European Roads Review, No. 2.
  3. Köppen, S. (2009). ISO 28580: Passenger Car, Truck and Bus Tyres — Method of measuring rolling resistance — Single point test and correlation of measurement results. Working Paper No. STD-01-05, 1st informal meeting, Joint GRB/GRRF Informal Group on Special Tyre Definitions (STD), United Nations Economic Commission for Europe, Geneva, Switzerland.
  4. Deraad, L.W. (1978). The Influence of Road Surface Texture on Tire Rolling Resistance. SAE Technical Paper Society of Automotive Engineers, Troy, MI. doi:10.4271/780257
  5. Descornet, G. (1990). Road-surface influence on tire rolling resistance. In Surface Characteristics of Roadways: International Research and Technologies. ASTM STP 1031. (W.E. Meyer & J. Reichert, eds.). American Society for Testing and Materials, Philadelphia, PA. pp. 401–415.
  6. Sandberg, U., A. Bergiers, J.A. Ejsmont, L. Goubert, R. Karlsson, & M. Zöller (2011). Road Surface Influence on Tyre/Road Rolling Resistance. Report MIRIAM_SP1_04. Danish Road Directorate, Copenhagen, Denmark.
  7. Zaabar, I., & K. Chatti (2011). A Field Investigation of the Effect of Pavement Surface Conditions on Fuel Consumption. In Proceedings of the TRB 90th Annual Meeting. Transportation Research Board of the National Academies, Washington, DC.
  8. Flügge, W. (1975). Viscoelasticity (2nd Revised Ed.). Springer-Verlag, Berlin, Germany.
  9. Walter, J.D., & F.S. Conant (1974). Energy Losses in Tires. Tire Science and Technology, 2, No. 4. pp. 235–260. doi:10.2346/1.2167188
  10. Bester, C.J. (1984). Effect of Pavement Type and Condition on the Fuel Consumption of Vehicles. In Transportation Research Record 1000, TRB, National Research Council, Washington, DC. pp. 28–32.
  11. De Graaff, D.F. (1999). Rolweerstand van ZOAB — een pilotstudie (Dutch Report: Rolling Resistance of Porous Asphalt — A Pilot Study). Report No. M+P.MVM.97.2.1, rev. 2, M+P, Vught, Netherlands.
  12. Pouget, S., C. Sauzéat, H. Di Benedetto, & F. Olard (2012). Viscous Energy Dissipation in Asphalt Pavement Structures and Implication for Vehicle Fuel Consumption. Journal of Materials in Civil Engineering, Vol. 24, No. 5, pp. 568–576. doi:10.1061/(ASCE)MT.1943-5533.0000414
  13. Stubstad, R. (2009). Fuel Efficiency Study of Concrete Pavements. Presented at The 2009 California Pavement Preservation Conference, April 8-9, 2009, Oakland, CA. http://www.techtransfer.berkeley.edu/pavementpres09downloads/stubstad_thurs_fuel-efficiency.pdf
  14. Akbarian, M., & F. Ulm. (2012). Model Based Pavement-Vehicle Interaction Simulation for Life Cycle Assessment of Pavements. MS Thesis. Concrete Sustainability Hub, Massachusetts Institute of Technology, Cambridge, MA. doi:1721.1/73847
  15. Sumitsawan, P., S.A. Ardenkani, & S. Romanoschi (2009). Effect of Pavement Type on Fuel Consumption and Emissions. In Proceedings of the 2009 Mid-Continent Transportation Research Symposium, Ames, IA.
  16. Velinsky, S.A., & R.A. White (1979). Increased Vehicle Energy Dissipation Due to Changes in Road Roughness with Emphasis on Rolling Losses. SAE Technical Paper Society of Automotive Engineers, Troy, MI. doi:10.4271/790653
  17. Du Plessis, H.W., A.T. Visser, & P.C. Curtayne (1990). Fuel consumption of vehicles as affected by road-surface characteristics. In Surface Characteristics of Roadways: International Research and Technologies. ASTM STP 1031. (W.E. Meyer & J. Reichert, eds.). American Society for Testing and Materials, Philadelphia, PA. pp. 480–496.
  18. Soliman, A.M.A. (2006). Effect of Road Roughness on the Vehicle Ride Comfort and Rolling Resistance. SAE Technical Paper 2006-01-1297. Society of Automotive Engineers, Troy, MI. doi:10.4271/2006-01-1297
  19. Van Dam, T.J., J.T. Harvey, S.T. Muench, K.D. Smith, M.B. Snyder, I.L. Al-Qadi, H. Ozer, J. Meijer, P.V. Ram, J.R. Roesler, & A. Kendall (2015). Towards Sustainable Pavement Systems: A Reference Document. Report FHWA-HIF-15-002. Federal Highway Administration, Washington, DC. www.fhwa.dot.gov/pavement/sustainability/ref_doc.cfm
  20. Smith, K.L., L. Titus-Glover, & L.D. Evans (2002). Pavement Smoothness Index Relationships, Final Report. Report FHWA-RD-02-057. Federal Highway Administration, McLean, Virginia. www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/02057
  21. Willis, J.R., M.M. Robbins, & M. Thompson (2014). Effects of Pavement Properties on Vehicular Rolling Resistance: A Literature Review. NCAT Report 14-07. National Center for Asphalt Technology, Auburn, AL. http://www.ncat.us/files/reports/2014/rep14-07.pdf
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