If you are a municipality concerned about safety - increase timer on yellow light.
It's not quite that simple. This has to do with how people learn a system and react to it.
You have a population that expects a warning a certain time before a condition applies. If you fiddle with the timing of when the warning comes up, the population will eventually learn the new timing and adjust to it. In the meantime they will either be surprised at a change in either direction. But shortening the light is more like "HOLY FUCK it's already red BRAKE SLAM" as opposed to "huh, I could have made it through this light".
But it's not quite that simple. You also have people from out of town that have learned their own light timing system and have an expectation when they visit you. You can essentially treat these people as people who haven't learned the new timing yet. And this is a bad thing because whenever you have two actors working on different systems they have different expectations and they both expect the other guy to do something different. We all expect to drive on the right side of the road in the USA, and we all have a general idea of how long a yellow light is supposed to last. It should be a rock-solid standard.
But it's not quite that simple. Even though there's a system and people learn it eventually, once it becomes a note-worthy thing and people start talking about it or worse, it becomes news, then you have the added factor of people preemptively stopping sooner or later. The benefit of having longer yellow lights is annulled if people know they're given a longer yellow light. Now you have people that haven't learned the new system, people who have learned the new system, and people who are trying to game the new system based on what they've heard.
Welcome to sociology where the factors are endless, the system is beyond our ken, and the points are billions of dollars and literal corpses.
I'd prefer if they didn't change the timing.