The Transportation Greenhouse Gas Inventory: A First Step Toward City-Driven Emissions Rationalization

As global warming becomes a leading public policy issue, we find ourselves with a local and regional government structure poorly equipped to deal with emissions from transportation. Reducing transportation emissions will require, among other measures, reductions in how much and how far people drive. Due to a tradition of local self determination, cities hold land use policy levers that in the long run will play an indispensable role in emissions reduction, but commute- and travel-sheds have grown well beyond city borders. In order to encourage cities to induce VMT reduction, some researchers have suggested that cities be included in a carbon economy. In order to be effective, this will require a carefully crafted emissions inventory that rationally guides cities in emissions reduction. This paper proposes a new inventory methodology with three key features. First, emissions are attributed to trip ends, rather than geographically. Second, new households receive an emissions credit or debit determined by the difference between their projected transportation emissions and the regional average household transportation emissions. Third, full transportation system life cycle emissions are included. Application of this inventory methodology to the City of Berkeley, California reveals that the methodology proposed here generates results substantially different from the presently used methodology.