C.R.S. § 42-4-602

(1) No local authority shall erect or maintain any stop sign or traffic control signal at any location so as to require the traffic on any state highway to stop before entering or crossing any intersecting highway unless approval in writing has first been obtained from the department of transportation. (2) Where practical no local authority shall maintain three traffic control signals located on a roadway so as to be within one minute’s driving time (to be determined by the speed limit) from any one of the signals to the other without synchronizing the lights to enhance the flow of traffic and thereby reduce air pollution.