Study Details
Study Title: Safety Impacts of Left-Turn Phasing Sequence
Authors: Qi et al.
Publication Date:JAN, 2009
Abstract: The safety impacts of left-turn phasing sequence have long been a discussion topic for traffic engineers. This research investigated the safety impacts of different types of left-turn signal phasing sequence under different types of left-turn signal control modes. It was found that, under protected-only (PO) control mode, lead-lag is the safest sequence, followed by the lead-lead and lag-lag sequences; under protected/permissive left-turn (PPLT) control mode, the lead-lead sequence is safer than the lead-lag sequence. In addition, the safety impacts of consistency of signal phasing were assessed by comparing the crash rates at four different corridor sections with different levels of mixed signal phasing sequences. It was found that the application of mixed signal phasing sequences increased the risk of crashes at intersections.
Study Citation: Qi, Y., L. Guo, and L. Yu, "Safety Impacts of Left-Turn Phasing Sequence." TRB 88th Annual Meeting Compendium of Papers CD-ROM. Washington, D.C., (2009).
CMFs Associated With This Study
Category: Intersection traffic control
Countermeasure: Change left turn phasing consistency from 27.3% to 9.1%
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.976 | 2.4 |  | All | All | Not Specified |
| 0.935 | 6.5 |  | Angle | All | Not Specified |
Countermeasure: Change left turn phasing consistency from 31.6% to 27.3%
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.922 | 7.8 | | All | All | Not Specified |
| 0.989 | 1.1 | | Angle | All | Not Specified |
Countermeasure: Change left turn phasing consistency from 61.9% to 31.6%
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.691 | 30.9 | | All | All | Not Specified |
| 0.642 | 35.8 | | Angle | All | Not Specified |
Countermeasure: Lag-lag to lead-lag left turn phasing
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.33 | 66.7 | | Angle | All | Not Specified |
Countermeasure: Lag-lag to lead-lead left turn phasing
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.31 | 68.5 | | Angle | All | Not Specified |
Countermeasure: Lead-lead to lag-lag, protected-only left-turn phasing
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 2.16 | -116 | | Angle | All | Not Specified |
Countermeasure: Lead-lead to lead-lag, protected-only left turn phasing
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.69 | 31.3 | | Angle | All | Not Specified |
Countermeasure: Lead-lead to lead-lag, protected/permissive left turn phasing
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.57 | -57 | | Angle | All | Not Specified |
Countermeasure: Protected/permissive to protected-only left turn phasing
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.5 | 50.2 | | Angle | All | Not Specified |
| 0.5 | 50.2 | | Angle | All | Not Specified |
