Smoothing Roadways at the Right Time to Cut Emissions

If you haven’t yet driven or bicycled along one of Philadelphia’s recently newly repaved streets (like Walnut or Chestnut), I suggest you give it a try.  The smooth surfaces of these streets not only make driving (and biking) much more comfortable but also decreases the rolling resistance for vehicles which helps limit carbon and other green house gas (GHG) emissions compared to a bumpy road with a high rolling resistance full of cracks and potholes.

Newly Repaved Walnut Street
(Photo Courtesy of

Since this is well understood, how come State and Municipal DOTs don’t repave all streets in order to lessen emissions?  A recent study by the University Of California Berkeley Institute Of Transportation Studies examined this issue and has showed that there are two influential factors at work.

First, when determining how to best decrease GHG emissions, it is necessary to view all potential solutions through the life-cycle of the road.  Resurfacing a large roadway can result in excessive GHG emissions, when accounting for the supply chain to repave – energy to mine the stone, producing the asphalt or concrete, the transportation of materials as well as operating construction equipment.

The UC Berkeley study looks at all different types of roads, from two lane rural roads to large interstates and determines the point at which repaving will lead to decreasing GHG emissions overall.

This curve identifies the best time to repave a street accounting for cost and emissions.
(from Berkeley ITS Report)

The second factor is the fiscal cost repaving roads.  Since DOTs do not have unlimited budgets, they must prioritize projects over others in order to make the best use of available resources.  In terms of environmental costs, this means comparing GHG emissions and dollars.  To account for this difference, the study compares the total life-cycle dollar costs per kilometer per year and the CO2 emissions per kilometer per year, thus identifying the interval when to repave a road to minimize the costs as well as the GHG emissions.

In Philadelphia, the Streets Department can use these metrics to identify when to repave roads in the city for the best price and to decrease the most carbon.  This will help the City of Philadelphia fulfill its Greenworks Goals to reduce 20% of emissions, as well as improve the quality of roads and transportation in the city.

Find out more at Berkeley ITS


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