Details
Type: Advisory
Topic or Program: Clarification of Change Interval Selection
Final Number: TR22-01(A)
Effective Date: 05/01/2022
Updated Date: 05/01/2022
Signature on File: Angela Kargel, PE - Interim State Traffic-Roadway Engineer
Purpose
The purpose of this technical advisory is to clarify acceptable yellow change and red clearance interval timing parameters for traffic signals on state highways.
Background/Reference
Practitioners shall continue to use the current ODOT Traffic Signal Policy and Guidelines as the basis from which they apply engineering judgment to select yellow change and red clearance intervals.
The standard kinematic equation was introduced by the Institute of Transportation Engineers (ITE) as a recommended practice in 1965. This equation has been revised four times through seven publications between introduction and 1999. The equation accounts for perception-reaction time, approach speed, deceleration, and in later variants, the approach grade. Additionally, in some variations a term is added to account for vehicle clearance. This term is now commonly applied as an all-red clearance interval.
In 2020 ITE introduced an extended kinematic equation aiming to account for different travel speeds and clearance times for turning vehicles. This extended equation frequently produces change intervals in excess of ODOT and MUTCD standards. Numerous jurisdictions did not expect improved safety or operations to result from adoption of the 2020 ITE guidance and expressed concern at user response to the magnitude of interval change the 2020 ITE guidance would produce. There was also concern from the greater traffic engineering community that the new guidance had not been tested or well vetted before publication. As a result, FHWA with 25 other State and Local Agencies, have entered into a pooled fund study to conduct further research on appropriate change and clearance interval timing. Details on the pooled fund study can be found here: www.pooledfund.org/Details/Solicitation/1536. ODOT will revisit the adopted practices when the pooled fund study is finished.