Signalized Intersections Appendix 2
Establishing a Clearance Interval
Methods for determining appropriate clearance interval length vary from agency to agency, and there is no consensus on which is the best method. The Institute for Transportation Engineers (ITE) recommends several procedures for determining clearance-interval duration in a 1994 informational report on signal change interval lengths. These methods include:
Formulas for calculating interval lengths based on site, vehicle, and human factors characteristics, such as this equation (Traffic Engineering Handbook):
A uniform clearance interval length
The Manual on Uniform Traffic Control Devices states that a yellow change interval should be approximately 3 to 6 seconds, and the Traffic Engineering Handbook states that a maximum of 5 seconds is typical for the yellow change interval. The red clearance interval, if used, should not exceed 6 seconds (MUTCD), but two seconds or less is typical (Traffic Engineering Handbook). The traffic laws in each state may vary from these suggested practices. ITE recommends that the yellow interval not exceed 5 seconds, so as not to encourage driver disrespect for signals.
Federal Highway Administration, Manual on Uniform Traffic Control Devices (MUTCD), Washington, D.C. 2003.
Institute of Transportation Engineers. Determining Vehicle Signal Change and Clearance Intervals. Washington, D.C. 1994.
Pline, J. L. Traffic Engineering Handbook. Institute of Transportation Engineers. 1999.