CMF / CRF Details

CMF ID: 2841

Converting four-lane roadways to three-lane roadways with center turn lane (road diet)

Description: Conversion of road segments from a four-lane to a three-lane cross-section with two-way left-turn lanes (also known as road diets).

Prior Condition:  Four-lane undivided roadway

Category: Roadway

Study: Comparison of empirical Bayes and full Bayes approaches for before-after road safety evaluations, Persaud et. al, 2010

Star Quality Rating:5 Stars  [View score details]
Rating Points Total:140
Crash Modification Factor (CMF)
Adjusted Standard Error:
Unadjusted Standard Error:0.02
Crash Reduction Factor (CRF)
Value:47  (This value indicates a decrease in crashes)
Adjusted Standard Error:
Unadjusted Standard Error:2
Crash Type:All
Crash Severity:All
Roadway Types:Not Specified
Street Type:
Minimum Number of Lanes:4
Maximum Number of Lanes:4
Number of Lanes Direction:
Number of Lanes Comment:
Crash Weather:Not specified
Road Division Type:Undivided
Minimum Speed Limit:
Maximum Speed Limit:
Speed Unit:
Speed Limit Comment:
Area Type:Urban and suburban
Traffic Volume:
Average Traffic Volume:
Time of Day:All
If countermeasure is intersection-based
Intersection Type:
Intersection Geometry:
Traffic Control:
Major Road Traffic Volume:
Minor Road Traffic Volume:
Average Major Road Volume :
Average Minor Road Volume :
Development Details
Date Range of Data Used:1982 to 2004
Type of Methodology Used:Before/after using empirical Bayes or full Bayes
Other Details
Included in Highway Safety Manual?No
Date Added to Clearinghouse:Mar 21, 2011
Comments:When this CMF was initially entered in the Clearinghouse, it was incorrectly entered as a CMF of 0.47. In March 2015, this was corrected to be 0.53, as presented in the original paper. In February 2021, the area type for this CMF was changed from suburban to urban/suburban to account for the fact that the treatment sites were largely located in small urban areas.