Define "signal progression".

Signal progression refers to the coordinated timing of traffic signals to improve flow along a corridor. This process involves the synchronization of traffic lights in such a way that vehicles can move smoothly from one intersection to the next without having to stop frequently, thereby minimizing delays and enhancing overall traffic efficiency.

By establishing signal progression, traffic engineers can create a progression wave, where signals are timed to turn green at intervals that match the speed of traffic, allowing vehicles to travel uninterrupted. This technique aims to balance flow and can lead to reduced congestion, improved travel times, and lower emissions from idling vehicles.

The other provided choices do not capture the essence of signal progression. The rotation of traffic lights at different times does not imply coordination to aid flow; it simply refers to individual signal operations. Immediate changes in signal color motivated by traffic demand pertain more to reactive signal operations than to progression. Finally, the activation of pedestrian signals at crosswalks focuses on accommodating pedestrian traffic rather than the overall vehicular flow along a corridor, which is central to the concept of signal progression.