Yellow Light Timing Traffic Laws - Do They Exist?

How long do yellow lights last?

Legislation mandating proper yellow light times is mostly non-existent. There are laws that forbids drivers from being in an intersection during a yellow light. The law is that the driver cannot be in the intersection during a red light. Although the difference is often a matter of a few split seconds, it is a major one.

The Federal Highway Administration's Manual on Uniform Traffic Control Devices recommends a yellow interval of three to six seconds but does not bind it to precise approach velocities. Anything dropping below the yellow timings listed below, on the other hand, could be regarded a possible short yellow light.

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

A lot of cities are adopting equations to figure out how to set their traffic lights instead of deciding on one uniform time per speed zone. According to a 2012 survey of 200 transportation agencies in the U.S., Canada, and Germany, 40% of the agencies use an equation by the Institution of Transportation Engineers to figure out their yellow lights.

yellow light math formula

The above kinematic calculation gives a more precise basis for establishing a traffic signal's minimum yellow light interval. The kinematic formula is used by many in the traffic engineering field to set a baseline for yellow light time, despite the fact that it is not a legal necessity in many states.

Calculating the yellow interval duration using the ITE-proposed formula (given in the next section of this page) and rounding up the result to the closest half second yielded the following table of actual vehicle approach speed vs. minimum yellow light times. These yellow light times are not required by law and cannot be used as a defense in court. However, they can be used as a guideline when determining whether a traffic signal's yellow light time is off. These times are for conventional passenger automobiles moving in through lanes, not turning lanes. They are insufficient for turn lanes or unusual situations involving huge trucks or buses.

We have a map to identify dangerous intersections with short yellow light times, which are exploited by red-light camera companies to keep violations and profits high.