Updated to support the protected left turn signals included in patch 1.2.
Increases the length of time that a yellow light lasts at a traffic signal from 2 seconds to 4 and a half seconds. I felt that the default 2 seconds was too short, if you have a heavy load it can be difficult to stop before the light changes red, causing you to receive a fine. In real life, yellow lights can range from 3 seconds to 6 seconds, so 4.5 seems like a good middle ground.
Tested on 1.2, but it should work on future versions too.