Determination of Left-Turn Yellow Change and Red Clearance Interval

Abstract

The yellow change and red clearance intervals for left-turn movements in right-hand-side driving environments are addressed on an analytic basis. Factors such as safety, perception, comfort, driver’s behavior, signal timing, and traffic ordinances are taken into account for setting the intervals. The yellow change interval for left-turn movements is found to be in general longer than that required for straight movements at intersections, because motorists usually slow down before making turns. Moreover, the required red clearance interval is derived in terms of the average curvature of a left-turn curve and the magnitude of acceleration that motorists are willing to bear on the curve. The calculated yellow change and red clearance intervals are in good agreement with the field observations for two signal-controlled intersections. The red clearance intervals in practice are shown to be short in comparison with the field observations and analytic estimates.