I Effectivenessof Priority Lanes in Reducing Travel Time and Carbon Monoxide Exposure

I n September 1975, the Federal Highway Administration (FHWA) and the Urban Mass Transportation Administration (UMTA) of the U.S. Department of Transportation issued joint regulations that required urban traffic planners and managers to make more efficient use of existing facilities for the purpose of expanding service and thereby avoiding increasing capital investment. 1 This federal program, known as Transportation System Management (TSM), among other things encourages use of contra-flow and with-flow (priority) lanes on a highway for the exclusive use of express buses, carpools, and vanpools. Priority lanes give these vehicles a speed advantage during their line-haul phase to compensate for the extra time they need to collect passengers. Some of the usual criteria for evaluating the effectiveness of priority lanes include passenger volumes, traffic safety, travel time, operating costs, and public attitudes. This study considers a new cri-terion—commuter exposure to motor vehicle exhaust inside the vehicle on the roadway. Carbon monoxide (CO) is commonly used as an indicator pollutant of exhaust because of its prevalence in tailpipe emissions and its nonreactivity. Study has shown that vehicle speed is a major factor affecting commuter CO exposure .' Thus commuters traveling in different lanes at different speeds may be exposed to different levels of CO in vehicle exhaust. This article discusses the results of an empirical study in Honolulu, Hawaii, to test the theory that priority lanes are effective in reducing not only commuter travel time, but also exposure to carbon monoxide. Honolulu is an ideal setting for testing this theory, because its background CO concentrations are negligible , Therefore, one can assume that the principal source of commuter CO exposure is surrounding traffic on a roadway. The study focused on a 4-mile segment of the Kalanianaole Highway (Figure 1), which is the sole connecting link between eastern Honolulu and the city's primary urban center (PUC). Of the corridors serving the PUC, this highway has the highest ratio (1.36) of one-way peak hour volume to capacity.' The vehicle mix consists almost entirely (97.1$%) of passenger cars and other light-duty vehicles , as this route primarily serves residential and light commercial areas.4 Coned-off contraflow and with-flow lanes, as depicted in Figure 2, are in effect during the morning peak period only. This 4-mile segment of the Kalani-anaole Highway is split into undivided and divided portions. The 1.9-mile un-divided portion (no median strip) extends from Kawaihae St. to the vicinity of Kirkwood St. …