Signal Timing Questions

You've got questions, we've got answers.

What is a "force-off"?

Force-off is the point during the cycle when the current timing phase's green interval ends and proceeds to yellow then red clearance. It is not a max or gap out, but rather in response to the amount of split time it gets, hence the term "force-off."

What is the cause and cure for erratic chatter with detectors?

Chatter is usually due to a loop detector with very high sensitivity.

Is flashing yellow arrow (FYA) mandatory in the United States?

It is not mandatory. The FYA has not been adopted by all agencies as they are still investigating its pros and cons. Some agencies prefer the flashing red over the yellow arrow.

What is the pedestrian scramble and how can my agency benefit?

The pedestrian scramble - also known as an 'X' or diagonal crossing - is a method of intersection control where all vehicular traffic is stopped to allow pedestrians to cross an intersection in all directions, including diagonally, at one time. It is ideal for intersections with high foot traffic, whether pedestrians regularly frequent the area or do so only on evenings or for special events.

By prohibiting people and vehicles from entering the intersection at the same time, the pedestrian scramble offers enhanced pedestrian safety.

What is the feature called, when the controller "remakes" a decision on next phases while in the yellow or red clear, and how common is it?

There is not a specific name for this functionality. Some intersection control programs can deviate from initial Phase Next decisions in limited scenarios, such as to serve an emergency or railroad preempt, while other programs do not deviate under any condition once committed to the Phase Next phases.

What are the pros and cons of double cycling?

Pros: It's perfect for smaller intersections in a corridor of heavier intersections with relatively light movements on the side streets that can be served quickly, such as neighborhood streets.

Cons: The location of the double cycling intersection could present an issue by possibly interfering with the progression of the main street platoon. Therefore, you would have to consider location carefully to avoid affecting the green band. Also, if there are side street peds during each cycle, it can cause delay for the main street phases.

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