Onboard unit for charging occupant number-dependent tolls for a vehicle in the context of a road toll system, comprising a Doppler radar or UWB impulse radar that can be directed onto the vehicle interior for measuring movements and generating at least one measurement signal representing these; and an evaluation device, which is configured to detect signal patterns in the measurement signal that are typical for heart or respiratory activity of an occupant, to count those signal patterns which occur simultaneously at an observation time, and to calculate toll data as a function of that count value.