Reducing Heavy Vehicle Idling
Anyone who has driven on interstate highways knows that big rigs idle overnight while their drivers sleep. The trucks are kept running to heat and cool the cab and sleeper, mask noises, keep the fuel warm in winter, avoid cold starting, and for personal safety. Long-haul trucks typically idle 6 hours per day, or 1,830 hours per year, but actual practice varies, from idling 1-2 nights per week to hardly ever turning the engine off.
Locomotives are also idled overnight and part of the day as well. These much larger engines (1,500-6,000 horsepower) produce larger fuel consumption and emissions effects per engine. Even though the crew does not sleep in the cab, they must remain ready while cars are changed or while the train waits on sidings for other trains to pass — sometimes for as long as 8 hours. In addition, heating is required to keep the engine warm overnight to make sure it starts and to keep the water in the toilet from freezing. Typically, switcher locomotives idle 75% of the time, accounting for 27% of their total fuel use.
 Each year, about 20 million barrels of diesel fuel are consumed by idling long-haul trucks. Estimated truck emissions total about 10 million tons of CO2, 50,000 tons of nitrogen oxides, and 2,000 tons of particulates. Several technologies are available that can reduce these effects by as much as 90%. The graph below shows how the percent of total fuel saved increases with the number of idling hours avoided. Technologies available for trucks include direct-fired heaters, auxiliary power units, thermal storage systems, and truck stop electrification. Most of these could be applied or adapted for use on locomotives, with even more dramatic results. Reducing locomotive idling by only 8 hours per day reduces total fuel use by over 11%. Actual savings could be even higher because locomotives often run in "high idle" (Notch 3) in cold weather, where fuel flow is six times as high as at normal idle.
To date, Argonne researchers have estimated the potential for locomotive energy savings and emission reductions as a result of implementing idling reduction and investigated the institutional factors that could impede implementation.
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