Passenger Car Unit

A Passenger Car Unit is a measure used primarily to assess highway capacity, for modelling purposes. Different vehicles are assigned different values, according to the space they take up. A car has a value of 1; smaller vehicles will have lower values, and larger vehicles will have higher values. 

The current Transport for London modelling values are shown in the table below (taken from here).

PCU values are also used by the Dutch cycle planners to give a truer reflection of the nature and density of traffic volume on a particular street. Rather than simply counting vehicles (as current British guidance does), the CROW manual uses PCU values. Thus if a relatively large number of HGVs and buses are travelling on a particular road or street, that will be captured by a PCU value, unlike a simple vehicle count. 

More suitable provision for cycling can then be used (for instance, greater separation), according to the PCU value.