On a typical weekday a transit bus idles for an average of 3.7 of the 9 hours that the bus is in operation. The analysis of the National Renewable Energy Laboratory’s Fleet DNA data included 415 conventional heavy-duty vehicles with over 120,000 hours of operation from 36 states. Combination-unit long-haul trucks had the next highest average idling times, but the highest average extended idling times, which are greater than one hour of continuous idling. Refuse trucks averaged 5.2 hours per day in operation but idled for 48% of that time.
- Idle is when a vehicle’s wheel speed is less than 1 mph and engine speed is greater than 0 rpm. Idling does not include additional “hoteling” activity from devices such as auxiliary power units, auxiliary battery power, auxiliary heating units, and other engine-off hoteling operations.
- Workday idle is an idling session of one hour or less.
- Extended idle is an idling session greater than one hour.
Source: National Renewable Energy Laboratory, MOVES Activity Updates Using Fleet DNA Data: Interim Report, NREL/TP-5400-70671, January 2019.