"The environmental impact from pavements has been misleadingly represented as stemming from only a few components in the life cycle," Nicholas Santero told environmentalresearchweb. "By focusing exclusively on processes associated with materials, transportation and construction, important areas of impact are overlooked. Rolling resistance, albedo, traffic delay, roadway lighting and carbonation are components of the pavement life cycle that are not usually assessed in existing pavement life-cycle assessments, but may pose significant environmental impacts."

Santero and colleague Arpad Horvath examined data for the five phases of the pavement life cycle – materials, construction, use, maintenance and end of life. The pair quantified global-warming potential ranges for each of the eight components making up these phases.

"Previously, there was no concept as to the impact of any one component relative to others in the life cycle," said Santero. "For instance, it was unclear as to whether materials, on-site equipment or traffic delay is the dominant component or whether they contribute relatively comparable impacts. The same lack of understanding is true of most of the other components as well. Understanding the relative importance of each component will provide valuable insight into best-practice methods to improving environmental performance."

Based on their findings, the researchers have developed a systematic approach for improving the environmental performance of a pavement. To maximize the efficiency of environmental improvements, they recommend prioritizing components with high-impact potential, since small changes in high-impact components will have more effect than large changes in low-impact components.

Typically rolling resistance would have the highest impact, with on-site equipment use and concrete carbonation having the lowest effect. However, factors such as the traffic loading, climate, structure and location of the pavement will all affect which components have the most sway.

"If a transportation agency or pavement contractor wishes to improve their carbon footprint, the most effective path is not necessarily the most obvious," said Santero. "Focusing on high-impact potential components, such as rolling resistance or traffic delay, may very well be a more effective reduction approach than fighting for marginal gains in more traditional areas such as materials production. However, each project is unique and thus there is no one-size-fits-all solution."

Of course, global-warming potential is only one of the environmental indicators for evaluating pavement. "Similar analyses using other metrics may produce significantly different results," said Santero. "For instance, although on-site equipment is shown to have low global-warming potential ceiling relative to the other life-cycle components, its human-health impacts will be much larger due to high exposure to carbon monoxide, particulate matter and other local pollutants."

The scientists believe that more research is needed to understand how other impact categories are affected by the components of the pavement life cycle

The researchers reported their results in Environmental Research Letters.