UC Davis Institute of Transportation Studies

Heavy-duty truck engine idling results in significant costs, fuel consumption, emissions, noise, and engine maintenance. Two promising alternatives to idling, grid connection ("shore power") and onboard auxiliary power units (APUs), are being pursued by industry and government. Their attractiveness is uncertain, however, because of limited information about truck operations and driver behavior. A nationwide survey of long-haul truck drivers was conducted to characterize truck operations and driver behavior better. Key variables included usage rates for accessories, duration of idling, and engine speed at idle. It was found that long-haul truck engines idled for an average of 34% of total engine run time, roughly 1,700 h per truck annually. But these averages are deceptive. Approximately 10% of drivers reported idling 10% or less of engine run time, while another 100;" reported idling more than 54% of engine run time, with differences related to season, truck ownership, company idling strategies, and driver experience. The mean annual fuel used during idle was estimated to be 1,600 gal per year, but the standard deviation was 1,300. An estimated 25% of drivers consumed more than 2,300 gal of fuel during idle (worth more than $3,000 per year in U.S. dollars), and 10% of drivers consumed more than 3,400 gal per year. These findings suggest that grid connections and APUs have the potential to provide large energy, environmental, and possibly even economic benefits.