Driver Exposure - Impact of Idle Reduction Technologies

Abstract

Long-haul truck drivers spend extended periods of time in the cabin of trucks, both while driving and during rest periods. Drivers rest in the truck cabin with the truck engine idling to provide air conditioning or heating. Past studies indicate that in-cab particulate matter (PM) concentrations are higher during truck idling than at other times. The exposure of drivers to pollutants in the truck cabin during idling/rest periods has emerged as an area of concern, due to short-term impacts such as drowsiness, fatigue, and long-term health impacts such as heart disease and lung cancer. Idle reduction is also being promoted as an emissions reduction strategy and fuel saving measure for trucks. Idle reduction technologies (IRTs) are commercially available to provide drivers with heating and cooling in the truck cabin. However, there is limited knowledge on the impact of IRTs on driver exposure to diesel exhaust. This study, performed for the Federal Motor Carrier Safety Administration, examined how effective IRTs are in reducing driver exposure to diesel exhaust, while considering their cost-effectiveness. The study focused on diesel-powered IRTs, specifically auxiliary power units and fuel operated heaters and their impact on particulate matter of 2.5 micrometers or less. A test protocol was developed to assess in-cab exposures of diesel-powered IRTs against baseline conditions, and for the truck engine idling. The testing included field data collection across 24 trucks stops in three states to establish representative ambient PM2.5 concentrations at truck stops, for use in the laboratory testing stage. Laboratory testing was conducted in an environmentally controlled test chamber to assess in-cab PM2.5 levels under baseline conditions, compared to the truck idling and use of different IRTs. Five trucks, ranging from Model Year (MY) 2006 to 2014 were tested. A cost analysis was also conducted to assess cost-effectiveness and payback period for various IRTs. The results indicated that both IRTs and idling the truck engine reduced in-cab PM2.5 level compared to ambient levels. It was also found that all trucks post-MY2007 did not exhibit self-pollution, i.e., in-cab PM2.5 levels did not increase on account of the truck or IRT’s own emissions. Keeping in mind overall emissions and fuel consumption benefits, the findings support the use of idle reduction technologies to reduce in-cab PM2.5 levels. The cost analysis indicated that all IRTs are economically feasible (with payback period under two years), with fuel operated heaters showing the shortest payback period.