Pre-Measure Your Carbon Footprint

Calculators help predict the environmental impact of roadbuilding projects

By Tom Kuennen, Contributing Editor

New tools keep appearing to help the highway, road and bridge community determine the environmental impact of the infrastructure they design and build.

Cold-in-place recycling of failed pavements optimizes use of in-place materials, relieving pressure on virgin aggregate extraction sites, on landfills, and greatly reduces truck trips with benefits to air quality, congestion, noise and reduced resource consumption.

Last month we looked at the proliferation of environmental certification programs available for highways (see Roadway Environmental Ratings: What’s Best for Your Agency?, November 2012, pp. 21-27). But in addition to these guidelines for a holistic summation of the environmental sustainability of a project, a plethora of environmental calculators now exist for a road builder to use in determining project sustainability in advance of construction.

These software-based eco-calculators allow an array of variables or “inputs” about a project – such as dimensions, materials, quantities, haul distances and equipment – and kick out data such as quantities of carbon dioxide emitted in construction or over the life of a project, other emissions and more. These data can provide a user with multiple paths to a sustainable project. In doing so a planner gets hard data projections he or she can use to justify or defend a project against those who would oppose it.

These calculators can be used in advance by an agency to establish project fundamentals, by a contractor to pose environmental alternatives that will favor his capabilities, or by consulting engineers to assist their agency clients.

For example, at the October semiannual meeting of the Asphalt Recycling & Reclaiming Association, Donald M. Matthews, P.E., of Pavement Recycling Systems in Riverside, Calif., said contractors can use the value engineering process – using environmental sustainability calculations – to suggest to clients that an alternate (in this case, cold-in-place recycling) could save time and money for a client.

“Use the calculations to suggest and prove that an alternative method will save an agency money, while providing them with an equal or better product,” Matthews says. “Sustainability calculators are valuable ways of showing even more benefit to an agency as agency personnel will get the pat on the back they deserve.”

Not surprisingly, eco-calculators first appeared in Europe, but now are making their way into North America. Some are proprietary and were developed by corporations for internal use; some are public domain, developed by government agencies; and some may promote one outcome or the other, depending on which business or national association is promoting it.

And contractors and agencies have been doing this type of evaluation in recent years without formal calculators. Using spreadsheets and their own knowledge, they’ve been able to informally determine the environmental impact of their projects.

National Asphalt Pavement Association’s Greenhouse Gas Calculator is an online tool that determines GHG emissions at the plant.

For example, in 2006, just by simple calculation that incorporated materials, quantities and truck trip inputs, Caltrans’ Joe Peterson, P.E. – now statewide chief of the Office of Roadway Materials Testing – was able to determine the benefits of an in-place recycling of busy I-80 through cities and countryside on the western slope of the Sierra Nevada.

“They saved approximately 112,200 short tons of aggregate, 2,860 tons of bitumen and 9,200 truck trips,” Robertson says in a presentation. “That’s an incredible number of truck trips, and that doesn’t include all the auxiliary equipment that would have been moving in and out of the work zone.”