Passenger car equivalent

Passenger Car Equivalent (PCE) or Passenger Car Unit (PCU) is a metric used in Transportation Engineering, to assess traffic-flow rate on a highway.^[1] 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 0.5
• bicycle 0.2
• horse-drawn vehicle 4
• bus, tractor, truck 3.5

Highway capacity is measured in PCE/hour daily

A common method used in the US is the density method. However, the PCU values derived from the density method are based on underlying homogeneous traffic concepts such as strict lane discipline, car following and a vehicle fleet that does not vary greatly in width.

On the other hand, highways in India, carry heterogeneous traffic, where road space is shared among many traffic modes with different physical dimensions. Loose lane discipline prevails; car following is not the norm. This complicates computing of PCE.

Using multiple heuristic techniques, transportation engineers convert a mixed traffic stream into a hypothetical passenger-car stream.

Methods

Many methods exist for determining passenger car units (PCUs)
examples:

• homogenization coefficient,
• semi-empirical method,
• Walker’s method,
• headway method,
• multiple linear regression method
• simulation method.

It may be appropriate to use different values for the same vehicle type according to circumstances. For example, in the UK in the 1960s and 1970s, bicycles were evaluated thus:

• on rural roads 0.5
• on urban roads 0.33
• on roundabouts 0.5
• at traffic lights 0.2.

References