Passenger car equivalent

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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. Traffic studies and/or analysis must be done to obtain the number of trips, which shall then be converted to PCUs based on the above standards. Each region has its own manual with regards to PCU equivalence factors. 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.