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)
Value: 0.701
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
State: LA
Country: USA
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.