Study Details

Study Title: Crash Modification Factor for an Inexpensive Yet Very Cost Effective Safety Improvement: Converting Undivided Four-Lane Urban Roadways to Five-Lane Roadways

Authors: Sun et al.

Publication Date:JAN, 2012

Abstract: Undivided multilane roadways have consistently exhibited low safety performance, particularly in urban or suburban areas where roadside development is relatively intense. Changing a four-lane undivided road to a divided roadway by either building a boulevard cross-section or installing a physical barrier is a desirable option to improve the safety performance, but it requires significant resources and sometimes a strong political will. This paper introduces a crash countermeasure successfully implemented on two different segments of urban undivided four-lane roadways in Louisiana. This crash countermeasure is to change an undivided 4-lane roadway to a 5-lane roadway with center lane for left-turn (TWLTL) by re-striping pavement markings without increasing pavement width. Although the five-lane roadway is no longer an acceptable roadway type for new construction in Louisiana, the impressive crash reductions on both roadway segments clearly demonstrate it as a feasible solution under constrained conditions. Based on the statistical analysis with six years of crash data (three years before and three years after excluding the project implementation year), the crash modification factors for both roadways are estimated to be less than 0.5 with a standard deviation less than 0.07. While it is not surprising to see the biggest crash reduction comes from the rear-end collisions, the other types of collisions are also reduced. The crash reduction is consistent for the time of day and by pavement surface condition (wet vs. dry). One-size-fits-all solutions do not always prevail in roadway safety. Under financial and other foreseeable or unforeseeable constraints, proactively doing something to reduce crash problems is better than just passively waiting for the probably unrealistic best solution. The tall order of the Louisiana Strategic Highway Safety Plan for Destination Zero Death on Louisiana roadways calls for all feasible crash countermeasures.

Study Citation: Sun, X., S. Das, N.P. Fruge, R.J. Bertinot, and D. Magri. "Crash Modification Factor for an Inexpensive Yet Very Cost Effective Safety Improvement: Converting Undivided Four-Lane Urban Roadways to Five-Lane Roadways." Presented at the 91st Annual Meeting of the Transportation Research Board, January 22-26, Washington, DC, 2012.

Related Citations: Sun, X., Das, S., Fruge, N., Bertinot, R.L., and Magri, D. "Four-Lane to Five-Lane Urban Roadway Conversions for Safety." Journal of Transportation Safety & Security, 5:2, 106-117. 2013. AND Sun, X. and S. Das. "Developing Louisiana Crash Reduction Factors", Lousiana DOT Final Report, FHWA/LA.12/506, October 2013.


CMFs Associated With This Study

Category: Roadway

Countermeasure: Four to five lane conversion

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.45552 StarsAllAllNot SpecifiedUrban
0.43572 StarsAllAllNot SpecifiedSuburban
0.18821 StarRear endAllNot SpecifiedUrban
0.56441 StarRear endAllNot SpecifiedSuburban
0.18821 StarWet roadAllNot SpecifiedUrban
0.42581 StarWet roadAllNot SpecifiedSuburban
0.38621 StarAllONot SpecifiedUrban
0.51491 StarAllONot SpecifiedSuburban
0.49511 StarAllA,B,CNot SpecifiedUrban
0.41591 StarAllA,B,CNot SpecifiedSuburban