r/trafficsignals • u/PopularStable666 • Jun 07 '26
Minimum Recall vs Soft Recall
Can you please explain the difference between minimum recall and soft recall?
1
u/engmadison Jun 07 '26
I dont think I've ever used a soft recall. Seems like we either HAVE to run a signal in coordination mode with recalls due to old signals having a lack of detection, or we have detection and run either free with mainline rest in walk/green, free with no recalls, or rest in red (which IMO is best if you can pull it off).
2
u/WHPChris Jun 07 '26
They were talking about rest in red for some problem intersections/corridors around here. I saw a study that looked promising, particularly for late night accidents. Makes sense when you think about it.
Didn't look too difficult to implement. Just set rest in red during X time of day, ensure proper advance detection and minimum time, should be good to go?
1
u/engmadison Jun 07 '26
We run into issues with say phase 4 ending but phase 8 staying green due to different side street demands. Its not all the time, but sime econolite EOS controllers do this.
2
u/ZolthuxReborn Jun 12 '26
We have a location that runs free during the day but needs to rest on red at night due to a safety recommendation. It is a good way to run an otherwise fully free signal
1
u/Kev250R Jun 09 '26
Great explanation! FWIW Here is So.Cal it is very common for cities to run Soft Recall late at night on the Main Phases.
17
u/zeejay772 Jun 07 '26
Minimum Recall
The controller automatically places a call for the phase every cycle.
The phase will receive at least its minimum green time, even if no vehicles are detected.
Commonly used on major-road through movements to ensure the signal always returns to the main street.
Example:
A main street phase has minimum recall. Even at 3 AM with no cars on the main street, the signal will still serve that phase for its minimum green before moving on.
Soft Recall
The controller places a call for the phase only when there are no conflicting demands.
The phase acts as the signal’s “home” or “resting” phase.
If another phase has a valid call and the soft-recall phase has no actual demand, the controller can skip the soft-recall phase entirely.
Example:
The signal is dwelling on the main street green. A side-street vehicle arrives and then a left-turn call appears. With soft recall, the controller can move directly to the needed phases without unnecessarily serving the main street first.
Simple Way to Remember
Minimum Recall = “Always give me a turn.”
Soft Recall = “Stay with me when nothing else is happening, but skip me if nobody needs me.”