Does the MUTCD allow changing from a stop-and-go signal operation to a flashing mode during low volume periods?
Yes, this is specifically allowed by paragraph 07 in Section 4D.28 of the 2009 MUTCD, but specific guidance is not given in the MUTCD on thresholds for such changes, which should be based on an engineering study or engineering judgment. Also, Section 4C.04 allows a signal warranted only by Warrant #3 (Peak Hour) to be operated in the flashing mode during the hours the volume criteria of warrant #3 are not met.
