Pavement smoothness is also a factor. The smoother a pavement is, the less fuel that will be required to propel vehicles along the roadway. Any roughness along the way will translate into vertical motion and consequently heat in vehicle suspension systems, leaving less energy available for forward motion. This concept is very similar to the hypotheses associated with rigid versus flexible pavements. Any energy that is “bled-off” to do such things as deflect the pavement, or excite the suspension system, will not be available to propel the vehicle forward. Hence, more energy is required to propel the vehicle, and fuel economy suffers.
A number of studies published since 1990 suggest there are significant fuel consumption efficiency gains associated with pavement smoothness gains. A Federal Highway Administration report published in 2000 suggests that a reduction in International Roughness Index (IRI) from 150 inches/mile to 75 inches/mile (i.e., improvement in smoothness) on asphalt pavement results in an accompanying 4.5 percent improvement in truck fuel economy.
These benefits are relevant not only for new pavements (i.e., specifying smooth pavements), but it is also important when deciding on maintenance strategies and schedules. Diamond grinding is a particularly useful technique used to restore pavements and improve smoothness. This can extend the service life of a smooth concrete pavement to twice its normal design life.
The other critical operational-phase impact that should be considered in a sustainability assessment relates to concrete pavement’s capacity to reflect light. This characteristic of pavement, generally referred to as albedo or solar reflectance, is a function of both type and age of the material. This has obvious visibility and safety implications, but the higher albedo that concrete pavement can provide is advantageous for other important sustainability-related reasons as well. High albedo pavements can significantly reduce the amount of energy needed for artificial roadway illumination during nighttime.
High-albedo or cool pavements can also reduce the amount of energy needed to cool urban environments associated with the urban heat island effect. Cool pavements can also mitigate the greenhouse effect and contribute to global cooling by reducing the amount of solar radiation absorbed by the earth’s surface.
The use of high albedo pavements has a significant sustainability impact and may even prove to be a useful tool in helping mitigate climate change. Moreover, because pavements remain in service for decades, lying exposed every hour of every day, the cumulative impact of these use factors over the pavement service life are enormous.
Leif G. Wathne is vice president-highways and federal affairs with the American Concrete Pavement Association (ACPA). Visit ACPA online at www.pavement.com.