How much energy does a car need on the road?

A car often requires more energy when driven in daily operation than indicated by the manufacturer. This paper presents a model to derive this real-world energy demand for a passenger car, based on a few widely available input data on vehicle operation. The approach works for conventional and alternative propulsion technologies. The underlying data stem from an extensive Swiss chassis dynamometer and on-road measurement campaign, which lasted for more than a year. The test fleet consisted of a compressed natural gas, gasoline hybrid, gasoline plug-in hybrid, fuel cell electric, and a battery-electric vehicle. The derived model adjusts the propulsive power demand within the legislative WLTP cycle for class 3b vehicles to a road mission by incorporating effects of traffic, driving styles, and topography. It additionally accounts for load from auxiliary devices. The approach works with input data from a household travel survey or traffic flow simulation and can serve as a tool to everyone who needs to estimate the average on-road energy demand of any passenger car or a fleet of them, rather than their type-approval values. Tested on a compact-sized vehicle, the approach estimates a mean discrepancy in real-world energy demand to WLTP type-approval values for Switzerland of about 22% for conventional cars. Furthermore, we can show similar gaps for hybrid technologies of around 30% and for battery-electric cars of 25%.