CMF / CRF Details

CMF ID: 10375

Install TWLTL (two-way left turn lane) on four lane road

Description: Converting 4-lane road to 4-lane plus one two-way turning lane.

Prior Condition:  Urban 4-lane undivided roadway

Category: Roadway

Study: Investigating Safety Impact of Center Line Rumble Strips, Lane Conversion, Roundabout and J-Turn Features on Louisiana Highways, Sun and Rahman, 2019

Star Quality Rating:4 Stars  [View score details]
Rating Points Total:130
Crash Modification Factor (CMF)
Adjusted Standard Error:
Unadjusted Standard Error:0.065
Crash Reduction Factor (CRF)
Value:29.9  (This value indicates a decrease in crashes)
Adjusted Standard Error:
Unadjusted Standard Error:6.5
Crash Type:Non-intersection
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
Traffic Volume:Minimum of 6800 to Maximum of 22141 Annual Average Daily Traffic (AADT)
Average Traffic Volume:
Time of Day:Not specified
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:2004 to 2016
Type of Methodology Used:Before/after using empirical Bayes or full Bayes
Sample Size (crashes):275 crashes before, 207 crashes after
Sample Size (sites):6 sites before, 6 sites after
Sample Size (miles):5.97 miles before, 5.97 miles after
Other Details
Included in Highway Safety Manual?No
Date Added to Clearinghouse:Jun 01, 2020
Comments:Safety performance function for 4-lane highway used for the analysis has been previously developed for the state of Louisiana.