Measuring the Effect of Level of Service on Vehicle Emissions

An ongoing research program at North Carolina State University, North Carolina, USA, is motivated by an overall objective to quantify the linkages between traffic performance and vehicle emissions. Empirical data are collected using a portable emission measurement device (PEMS) that simultaneously measures micro-scale vehicle dynamics and emissions in a real-world setting. These data are used to evaluate the relationship between average link speed and emissions for light-duty vehicles on several facility types including freeways, ramps and signalized arterials. Since average link speed is an indicator of traffic Level of Service (LOS) for these facilities, a more direct tie between LOS and emissions can be established. The proposed procedure, when supplemented with larger data samples, can be used to extend Highway Capacity Manual (HCM) models to include environmental considerations. In general, pollutant emission rates (in gm/sec) increased with the average link speed for all facilities. However, since the total emissions also depend on the amount of time spent on a link, the total emissions on a link could increase or decrease depending on the travel time and the pollutant considered.