significant improvements can be achieved simply by considering these important factors in the selection process used for pavements. At present, most decisions are based on first cost, and to a limited degree life-cycle cost. New, more comprehensive selection processes could take these very real agency- and societal-impacts into consideration.

"A stronger federal position on the use of federal-aid funds, coupled with an objective and more comprehensive pavement selection policy, would help ensure state transportation agencies and others effectively apply appropriate considerations for energy use and sustainability," he said.

He added concrete pavements are inherently more sustainable than asphalt pavements, and then said there are a number of energy-related factors that are not presently considered in the typical pavement-type selection processes used by state transportation departments. Among those considerations is the energy required to build pavements and the energy consumed by vehicles to drive on pavements once they are opened to traffic.

Concrete Pavements, Naturally
Citing other environmental features and benefits of concrete pavements, Voigt said:

• Concrete pavements inherently have the lowest overall energy footprint. The reasons for this are many, but the primary factors are the exceptional longevity of concrete pavements; the relatively low amounts of fuel required to place concrete pavements; and, of course, the fact that concrete is not a byproduct of petroleum refining and production, and thus, has much lower embodied primary energy (including feedstock energy.)" ²
• Most pavements are placed with a targeted design life of 20 years, but concrete pavements generally last much longer. In fact, he said, there are well-documented cases of heavily trafficked concrete pavements that have performed for longer than 40 years, while most asphalt pavements last less than 20 years.
• Concrete is 100 percent recyclable and reusable. Routinely, old concrete is crushed, steel components are removed and recycled, and then, the crushed concrete is used for roadbed materials, for stormwater management, for aggregate in new concrete mixtures, and also for some non-paving applications.
• Construction of hot-mix asphalt roadways consumes more than five times as much diesel fuel as the construction of comparable concrete roadways. ³ Approximately 1.2 billion gallons of diesel fuel could be saved annually if comparable asphalt pavements were built with concrete. This would be equivalent to taking 2.7 million cars off the road annually. ⁴
• Trucks traveling on concrete pavements use between 0.8 percent to 6.9 percent less fuel. ⁵ If the 59 percent of the 160,000 lineal mile National Highway System were converted to concrete pavements, the annual savings would be 2.1 billion gallons of diesel fuel per year, or roughly $8.2 billion dollars (based on diesel fuel prices at $4.00/gallon). This also would reduce the nation's dependence on oil; lower the emissions from vehicles; and decrease the cost of transporting goods.
• Concrete pavements are also naturally light-colored, reflect light and do not retain as much heat as darker-colored asphalt pavements. This enhances night-time visibility, which in turn, improves both pedestrian and vehicle safety. These properties also can have a profound effect on energy savings, as it requires fewer lighting fixtures or lower wattage fixtures to illuminate concrete roadways in comparison to the darker asphalt surfaces. When properly accounted for during design, cities and municipalities can save up to 1/3 on energy costs associated with street-lights.

Voigt also noted that cement represents only about 8 percent of a typical concrete pavement (by volume). He added member companies of the American Concrete Pavement Association and Portland Cement Association have voluntarily adopted four goals aimed at improving environmental performance:

• Carbon Dioxide—Reduce carbon dioxide emissions by 10 percent (from a 1990 baseline) per ton of cementitious product produced or sold by 2020.
• Cement Kiln Dust—Reduce the disposal of cement kiln dust by 60 percent (from a 1990 baseline) per ton of clinker produced by 2020.
• Environmental Management Systems—At least 75 percent of U.S. cement plants will implement an auditable and verifiable environmental management system by 2010 and 90 percent by 2020.
• Energy Efficiency—Improve energy efficiency by 20 percent (from a 1990 baseline) as measured by total Btu per unit of cementitious product by 2020.

Voigt said in the past two decades, there has been a trend toward using less portland cement to be used per cubic yard of concrete. He attributed this to improved mixture technology, as well as the industry's use of industrial by-products, such as fly ash (from coal-fired energy plants) and slag (from iron blast furnaces), to replace cement. Cement manufacturers also have developed new products where these supplementary materials are combined during manufacturing as a blended cement product.

Current and Future Needs
Voigt cited specific research projects being conducted or facilitated by ACPA, the National Concrete Pavement Technology Center (CP Tech Center), and Arizona State University's National Center of Excellence on SMART Innovations for Urban Climate and Energy.