The Impact of a Bus Rapid Transit System on Commutersʼ Exposure to Air Pollutants in Mexico City

Abstract

MS7-07 Abstract: Bus rapid transit (BRT) systems are being implemented in cities all around the world as a sustainable alternative to conventional public transport, providing a more rapid, metro-like service with separated busways. In addition, the use of modern engine technology leads to reduced vehicular emissions and environmental impact. These factors may further result in a benefit to users of the BRT system due to reduced personal exposures to on-board air pollutants. To our knowledge, this benefit has never before been evaluated experimentally in a Latin American city. The objective of this study was to determine the reduction in commuters’ exposure to air pollutants that may result from a change from a conventional bus transport system to a BRT system in Mexico City. During the summer of 2004, personal exposures to particulate matter (PM2.5 and PM10), benzene, and carbon monoxide (CO) were measured inside 37 conventional buses and 36 minibuses during the morning rush hour along one of the main avenues of Mexico City. During the summer of 2005, after the substitution of the conventional transport modes by a new BRT system with new vehicles, these air pollutants were again measured in 63 BRT buses on the same route. Portable sampling pumps, canisters, and sensors were deployed for these measurements. Significant reductions in personal exposures inside vehicles of the BRT system were found for air pollutants associated with vehicular emissions. Median personal PM2.5 exposures dropped from 152 μg/m3 and 129 μg/m3 inside conventional minibuses and autobuses, respectively, to 99 μg/m3 in the interior of vehicles of the BRT system. Even greater relative reductions were observed for personal benzene exposures, which dropped from 10.2 ppbv and 8.9 ppbv in minibuses and autobuses, respectively, to 4.2 ppbv in BRT vehicles. Similarly, personal CO exposures dropped from 15.8 ppm and 11.4 ppm in minibuses and autobuses to 7.5 ppm in BRT vehicles. However, personal PM10 exposures were not significantly different between conventional transportation modes and BRT vehicles. Finally, commuting times were reduced by approximately 20% in BRT vehicles. These findings show the potential of BRT systems to reduce in-vehicle concentrations of air pollutants in comparison to conventional transport modes. The additional reduction of commuting times further decreases total exposure and thus the health impact of commuting. Therefore, the installation of BRT systems should be encouraged as a means to decrease population exposure to air pollutants, shorten commuting times, and thus elevate the quality of life of public transport users.