Improved Red Clearance Intervals Based on Observed Turning Times for Left-Turn Movement

Abstract

Because of the lack of adequate guidelines and procedures to determine the red clearance interval for the left-turn movement, a common practice for most jurisdictions is to use the same red clearance intervals for both through and left-turn movements. Such a practice may create potential safety and operational concerns because the unique characteristics of left-turn traffic, such as the presence of turning curves and centrifugal forces, are not addressed. To improve the calculation of the red clearance interval for the left-turn movement, a new method was developed and verified by data observed in the field. The actual turning times were collected at 21 intersections in Texas. These intersections vary in speed limit, number of left-turn lanes, and left-turn control type. The red clearance intervals, determined from the proposed methodology, were generally lower than the turning times observed in the field but higher than those currently being used in practice. A validation of the calculation based on the crash analysis was also conducted to support the proposed method.