An Evaluation of Ramp Control Signal Head Placement Based on Motorist's Cone of Visions

ABSTRACTRoadside mounted ramp control signals have one upper head, and one lower head in California. The upper head is intended for use by the approaching motorists, while the lower one for use by the stopped motorists. Complaints have been received regarding the visibility of these signal heads. The evaluation presented in this paper is to mathematically analyze the visibility of these signal heads on a tangent roadway alignment based on satisfactory motorists' cones of vision. Roadway design, signal placement, and driver characteristics are integrated into one analytic framework. The results indicated that the horizontal satisfactory cone of vision controls the placement design. To meet the 20 degree satisfactory horizontal cone of vision as specified by the Manual on Uniform Traffic Control Devices (MUTCD), a ramp control signal head has to be placed a minimum of 13.3 m downstream of the limit line.