A comparison of the energy uses of gasoline and electric vehicles under on-road commuter driving conditions

The purpose of this study was to assess the energy efficiency of For electric and gasoline vehicles under on-road driving conditions. this purpose, an experiment between an electric and a gasoline vehicle was conducted along a typical commuter route in Knoxville, Tennessee. The vehicles were chosen to be structurally comparable, thus controlling for the effects of nonpropulsion components. The vehicles were operated in tandem for five days (Monday through Friday) during the morning and afternoon peak hours of traffic; the gasoline vehicle was constrained to follow the electric vehicle. Within each time period the vehicles were driven in both peak and nonpeak directions. An appropriate experimental design was chosen so that several drivers could be randomly assigned to vehicle operation.

The energy consumption of both vehicles was monitored during the tests. The gasoline vehicle's energy consumption was monitored using a simple measuring technique while that of the electric vehicle was recorded using a strip chart device. Also collected during the course of the experiment were a speed/time history of the vehicle trips for use in the computer program RUNCOST; this provided an additional estimation of gasoline use. This data was also used to correlate the vehicles' energy uses to trip-related variables.

There are several results and conclusions that were drawn from the research. The electric vehicle proved to be approximately 25 percent more energy efficient than the gasoline vehicle in terms of propulsion energy. From a systems viewpoint, however, the gasoline vehicle was found to be nearly twice as efficient. The energy economy of the electric vehicle was not influenced to an appreciable degree by trip-related variables such as travel time; number and duration of stops; and average running speed. Good relationships were found between these variables and the fuel consumption of the gasoline vehicle. The efficiency of the charger/battery/controller system in the electric vehicle was found to be 45.1 percent. Also, procedures were developed to convert manually collected speed/time data into an appropriate input form for RUNCOST and a method of updating RUNCOST to replicate the performance of current fuel efficient cars was developed, tested, and found to give reasonable results. Recommended areas of further research include the effect of charger operation, especially "topping charge", on electric vehicle energy economy; the effects of roadway geometrics on electric vehicle fuel economy; tests of additional gasoline vehicles on a variety of routes to develop quick response estimations of fuel consumption; and assessing the impact of not driving the vehicles in a tandem fashion.