Practical reserve capacity

In traffic engineering, the practical reserve capacity (PRC) of a traffic signal junction is a commonly used measure of its available spare capacity.

The practical reserve capacity is related to the degree of saturation of a traffic signal junction. A positive PRC indicates that a junction has spare capacity and may be able to accept more traffic. A negative PRC indicates that the junction is over capacity and is suffering from traffic congestion.

A PRC value is calculated by the commonly used traffic signal modelling software LINSIG.

...
Wikipedia