City, State & Federal legislation regulating traffic light yellow light times is mostly non-existent. However, studies have shown that an increase of 0.5 to 1.5 seconds in yellow-light duration will decrease the frequency of red-light running by at least 50 percent. Three seconds should be the absolute minimum time for any intersection. Here are the standards recommended. See the details at Standard Yellow Lights from the National Motorist Association Foundation
25 MPH -- 3.0 Seconds
30 MPH -- 3.5 Seconds
35 MPH -- 4.0 Seconds
40 MPH -- 4.5 Seconds
45 MPH -- 5.0 Seconds
50 MPH -- 5.5 Seconds
55 MPH -- 6.0 Seconds