Study Details
Study Title: Comparative Analysis of Leading and Lagging Left Turns
Authors: Lee et al.
Publication Date: 1991
Abstract: This project was undertaken to compare operational and safety characteristics of leading verses lagging protected left turn operation. The measures of effectiveness included field measured intersection delay with leading and with lagging left turns. Intersections in Pima County, Glendale, Tempe and Mesa, Arizona were studied with both leading and lagging operation. Intersection delay studies were also done with first car verses third car actuation of leading protected left turn phases. Signal progression was studied with leading, lagging and combination of leading and lagging left turns which provided the best progression. This evaluation was accomplished with an instrumented vehicle and travel time runs throughout a grid. Accident studies were conducted in Tucson, Pima County and Scottsdale, Arizona. These studies compared accident frequency before and after the conversion from leading to lagging left turns. A public opinion survey was conducted to obtain motorists' preference of leading or lagging left turns.
Study Citation: Lee, J. C., Wortman, R. H., Hook, D. J., and Poppe, M. J., "Comparative Analysis of Leading and Lagging Left Turns." Phoenix, Arizona Department of Transportation, (1991)
Study Report: Download the Study Report Document
CMFs Associated With This Study
Category: Intersection traffic control
Countermeasure: Leading protected to lagging protected exclusive left-turn operations
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.49 | -49 |  | Angle | All | Not specified | Not specified |
| 1.15 | -15 | | All | All | Not specified | Not specified |
Countermeasure: Protected / Permitted to Permitted / Protected
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.87 | 13 | | All | All | Not specified | Not specified |
Countermeasure: Protected/permissive to permissive/protected left-turn operations
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.67 | 33 | | Angle | All | Not specified | Not specified |
