Measuring Impacts of High-Occupancy-Vehicle Lane Operations on Light-Duty-Vehicle Emissions

Abstract

High-occupancy-vehicle (HOV) lanes on urban highways have long been proved to increase the efficiency of highway operations, as measured by person throughput, vehicle occupancy, travel time, speed, and reliability. Operational measures of effectiveness, such as speed and travel time, for HOV facilities are superior to general purpose (GP) lanes, in which predominantly single-occupancy vehicles operate. Few studies have attempted to study the emissions on HOV facilities vis-à-vis their GP lane counterparts. In this research, differences in vehicle emissions between HOV lane and GP lane facilities were measured with portable emissions sensors. Several hundred miles of on-road emissions data were collected by vehicles instrumented with portable emissions-monitoring systems (PEMSs) operated in HOV and GP lanes during peak hours in the metropolitan Washington, D.C., area. Data were collected at HOV facilities with buffer separation and at HOV facilities with barrier separation (limited-access lanes). Experimental runs were conducted with pairs of nearly identical instrumented vehicles that simultaneously began trips in parallel HOV and GP lanes and ended them at a common location. The experimental design controlled for vehicle type and driver characteristics. Analysis identified the emissions profiles of vehicles operating in barrier-separated HOV lanes (I-95) and vehicles operating in buffer-separated HOV lanes (I-66). Experiences related to the experimental design with the PEMS, the field deployment of the PEMS, data collection, and analysis are discussed. Included in the discussion is a description of the application of a geographic information system for data reduction and analysis.