Estimating Greenhouse Gases from Roadway Transportation—Methodology Overview

Since Greenhouse gases (GHG) are believed to lead to global warming, emission of such gases are now considered an environmental threat that must be confronted. About 30% of the GHG emissions in the United States are from transportation sources. This is why, transportation planners, policy makers, and the public often wants to know what effects a transportation project or a policy decision will have on GHG emissions. How to estimate GHG emissions in planning stage of a project or at policy decision levels? The standard process involves running a travel demand model as well as a sophisticated vehicle emission model. Data requirements of most of these emission modeling tools strain the ability of travel demand models to produce inputs at sufficiently fine detail. Moreover, due to emission model's complexity, time-consuming data collection, and staff and project budget constrains, it may not be feasible for transportation professionals to apply such sophisticated tools for estimating vehicle emissions for all transportation projects. Rather a quick and easy approach would help planners/engineers to apply travel demand model for vehicle emission estimation. The purpose of this paper is to provide an overview of methodologies that can help estimate GHG emissions without requiring too much of difficult to find data. This paper will first provide an overview of the common approaches about applying travel demand modeling data for roadway vehicle emission estimation. Several quick and easy vehicle emission estimation approaches will then be described.