Study Details

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

Authors: Sun and Rahman

Publication Date: OCT, 2019

Abstract: Over the past several years, Louisiana has installed quite a few relatively new crash countermeasures, such as center line rumble strips (CLRS) on rural two-lane highways, restriping four-lane undivided roadways to three-lane or five-lane roadways with center lane for left turns, restricting median openings on high speed corridors (RCUT), and roundabouts. Evaluating the effectiveness of these crash countermeasures is crucial for the state highway safety improvement programs. According to the results of this study, these four countermeasures are generally cost-effective and successful in reducing crashes, particularly severe crashes. Estimated crash modification factors (CMFs) for total crashes are 0.83 for CLRS by the Empirical Bayes (EB) method. The CMF for the lane conversion to three and five-lane highways are 0.61 and 0.70 by EB method for segment, and 0.69 and 0.76 by Improved Prediction Method for segment plus intersection. The CMF for RCUT is 0.86 and 0.69 by Improved Prediction Method for RCUT section and intersection only. The CMF for RCUT intersection only is 0.80 by EB method. The CMF for roundabout with stop-sign on minor street (without layout change) is 0.32 and 0.28 by Improved Prediction and EB method. Except roundabout, the ratio of benefit to cost (B/C) is bigger or much bigger than one. Being the most expensive countermeasure, the B/C ratio of roundabout is less than one, but that estimation did not count the benefit from the improved traffic flow performance (reduced delay or saving in travel time) and long-time safety benefits (only three after years).

Study Citation: Sun, X., and S. Rahman "Investigating Safety Impact of Center Line Rumble Strips, Lane Conversion, Roundabout and J-Turn Features on Louisiana Highways" Report No: FHWA/LA.18/597. Louisiana Department of Transportation and Development. Baton Rouge, Louisiana. (October 2019).

Related Citations: Sun, X., Y. He, M.A. Rahman, and K. McManis. "Safety of Roundabout: The Details Matter". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-00871, Washington, D.C., (2018).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Convert intersection to restricted crossing U-turn (RCUT) intersection

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.86 2 Stars All All Not specified All
0.69 31 2 Stars All All Not specified All
0.87 13 2 Stars All All Not specified All
1.06 -6 2 Stars All All Not specified All
0.77 23 2 Stars All All Not specified All
0.8 20 4 Stars All All Not specified All
0.8 20 4 Stars All All Not specified All
0.42 58 4 Stars All All Not specified All
1.07 -7 3 Stars All All Not specified All

Category:Roadway

Countermeasure: Install centerline rumble strips

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.831 16.9 5 Stars All All Not specified Rural

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.758 24.2 2 Stars All All Not specified Urban
0.701 29.9 4 Stars Non-intersection All Not specified Urban

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
0.688 31.2 2 Stars All All Not specified Urban
0.613 38.7 4 Stars Non-intersection All Not specified Urban