Guidelines for Left-Turn Phasing Treatment

Abstract

The safety of left-turning vehicles at signalized intersections is a concern of the safety community, and guidelines for the installation of left-turn phasing have been developed. The development of guidelines to be considered when determining whether left-turn phasing should be used and the type of phasing that would be appropriate is presented. The guidelines are based on accident data collected for 408 approaches in Kentucky and delay data simulated for a variety of intersection characteristics. The recommendations made take into account many variables, including left-turn volumes, accident rates, product of opposing and left-turn volumes, and left-turn delays. A two-step approach is considered in the decision whether to install left-turn phasing: determine whether protection is needed and then determine the type of protection. The selection of the appropriate left-turn treatment is a process in which trade-offs between safety and delays may be required. Moreover, the use of single rules is usually not adequate to determine the appropriate left-turn treatment; a variety of other factors must be considered.

A simulation-based approach in determining permitted left-turn capacities

“…For each of these scenarios, they identified a set of crash and volume combinations to be used in making the choice of phasing type. It should be noted that most of their findings were in agreement with the Stamatiadis et al (1997) study. Clark and Daniel (1994) also proposed a similar set for left-turn phasing for South Carolina.…”

Using visual data mining in highway traffic safety analysis and decision making

“…The sensor captures whenever a motor vehicle passes the location and counts for a record. It is important to note that traffic volume is one of the measures traditionally used to normalize accident data (Gregoriades et al, 2011; Ivan, 2004;Laessig & Waterworth, 1970;Stamatiadis, Agent, & Bizakis, 1997). However, the estimation of the target variable may contain misleading information because the traffic volumes vary by location and time.…”

Signalized Intersection Level of Service Incorporating Safety Risk

“…According to accident statistics, 45% of all accidents occurring at intersections in the United States involve left-turning maneuvers, although only 10% to 15% of all intersection traffic turns left (23). Exclusive left-turn phasing reduces right-angle and pedestrian accidents significantly (24)(25)(26)(27)(28).…”