Mo. Rev. Stat. § 304.289: Timing of signals, minimum interval times to be established.

The timing of any traffic-control signal shall conform to regulations promulgated by the Department of Transportation . The department of transportation shall establish minimal yellow light change interval times for traffic-control devices. The minimal yellow light change interval time shall be established in accordance with nationally recognized engineering standards set forth in the Manual on Uniform Traffic Control Devices, and any such established time shall not be less than the recognized national standard.