Study Details
Study Title: Safety and Operational Analysis of 4-lane to 3-lane Conversions (Road Diets) in Michigan
Authors: Lyles et al.
Publication Date:JAN, 2012
Abstract: Road diets, specifically 4-to-3 lane conversions, implemented in various locations in Michigan were studied to determine the safety- and delay-related impacts, develop crash modification factors (CMFs), and develop guidelines that would be useful in deciding when it might be desirable to implement such road diets. The results of the operational analysis support a guideline that suggests that 4-to-3 lane conversions result in significant delay when average daily traffic (ADT) exceeds 10,000 and, more importantly, when peak hour volumes exceed 1,000. A CMF of 0.91 (after adjustment for background citywide trends) for all crash types is recommended although the factor is not statistically different from 1.0. There was considerable site-to-site variation among the 24 sites studied, and this should always be considered when a road diet is contemplated. A study-by-study literature review and suggestions for implementation strategies are also included.
Study Citation: Lyles, R.W., M.A. Siddiqui, W.C. Taylor, B.Z. Malik, G. Siviy, and T. Haan. "Safety and Operational Analysis of 4-lane to 3-lane Conversions (Road Diets) in Michigan". Michigan Department of Transportation Report Num RC-1555, (2012)
CMFs Associated With This Study
Category: Roadway
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane)
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.95 | 5 |  | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - 8 or less intersections
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.95 | 5 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - 8 or less intersections, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.61 | 39 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - 9 or more intersections
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.93 | 7 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - 9 or more intersections, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.55 | 45 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - commercial areas
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.05 | -5 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - commercial areas, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.72 | 28 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - high crash areas
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.91 | 9 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - high crash areas, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.54 | 46 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - high driveway density
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.81 | 19 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - high driveway density, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.51 | 49 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - low crash areas
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.98 | 2 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - low crash areas, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.63 | 37 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - low driveway density
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.07 | -7 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - low driveway density, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.66 | 34 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - mixed use areas
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.06 | -6 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - mixed use areas, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.52 | 48 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - residential areas
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.77 | 23 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane) - residential areas, target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.51 | 49 | | All | All | Not specified |
Countermeasure: Road diet (Convert 4-lane undivided road to 2-lanes plus turning lane), target crashes
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.59 | 41 |  | All | All | Not specified |
