Whenever I am driving I try to speed through the light when it is yellow and it is always stressful trying to get through before it becomes red. Street crossing lights have a countdown number that tells the walker how long until the light changes. Why isn't a similar thing implemented on traffic lights?
Actually there are examples of this in different countries, or at least I have seen it in Shanghai before.
There are a lot of reasons behind whether systems like this can be implemented or not, but a traffic engineer might provide a more accurate answer. But in general these are the considerations that I know: