Passenger car equivalent (PCE) or passenger car unit (PCU) is a metric used in transportation engineering, to assess traffic-flow rate on a highway. A passenger car equivalent is essentially the impact that a mode of transport has on traffic variables (such as headway, speed, density) compared to a single car. For example, typical values of PCE (or PCU) are: * private car (including taxis or pick-up) 1 * motorcycle 0.75 * bicycle 0.5 * horse-drawn vehicle 4 * bus, tractor, truck 3 Highway capacity is measured in PCE/hour daily