Which of the following is NOT a typical functionality of transit priority systems?

Transit priority systems are designed to enhance the efficiency of public transportation by enabling buses and other transit vehicles to have priority at traffic signals. This is crucial for reducing delays and improving adherence to schedules.

Among the functionalities typical of these systems, green light extension allows for an existing green signal to be extended when a transit vehicle approaches, minimizing wait times. Red light extension involves allowing a transit vehicle to have more time when the light is red, although this is less common and context-dependent. Red truncation is a strategy where the red phase of a signal is shortened when a transit vehicle approaches, facilitating quicker passage through intersections.

The option identified as not a typical functionality is green light retraction. This would imply shortening the green signal time for vehicles already in the intersection to accommodate transit vehicles, which contradicts the purpose of transit priority systems. Such a retraction would not service the goals of enhancing transit efficiency, as it would generally create more delays for both transit vehicles and regular traffic.