Study Details

Study Title: Safety Evaluation of Curve Delineation Improvements An Empirical Bayes Observational Before-After Study

Authors: Montella

Publication Date:JAN, 2009

Abstract: The objective of this study was to evaluate the safety effectiveness of treatments aimed at improving horizontal curve delineation. Different target crash types were considered in the analysis: total, nighttime, daytime, rainy, non rainy, run-off-road, non run-off-road, injury, property damage only. The treatment sites for this study were 15 curves of the motorway A16 NaplesCanosa, in Italy. All the curves are characterized by low radius, high deflection angle, available sight distance smaller than the stopping sight distance, and superelevation smaller than the demanded one at both the design and the operating speed. Treatments typologies were: installation of chevron signs; installation of curve warning signs and chevron signs; installation of curve warning signs, chevron signs and sequential flashing beacons along the curve. An empirical Bayes observational before-after study was performed. Results indicate statistically significant crash reductions in total, nighttime, daytime, rainy, non rainy, run-off- road, and property damage only crashes. Estimate of total crashes reduction is equal to 39.4%. Treatment effectiveness is greater for curves with radius less than or equal to 300 m and for curves with deflection angle greater than 60 gon. Estimate of total crashes reduction is equal to 52.2% for curves with radius less than or equal to 300 m and equal to 51.0% for curves with deflection angle greater than 60 gon. Most effective treatment resulted the installation of curve warning signs, chevron signs and sequential flashing beacons along the curve. Statistically significant total crashes reduction estimate for this treatment is equal to 47.6%.

Study Citation: Montella, A. "Safety Evaluation of Curve Delineation Improvements An Empirical Bayes Observational Before-After Study." TRB 88th Annual Meeting Compendium of Papers CD-ROM. Washington, D.C., (2009).


CMFs Associated With This Study

Category: Signs

Countermeasure: Install a combination of chevron signs, curve warning signs, and/or sequential flashing beacons

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.72283 StarsAngle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.56843.24 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.43574 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.60639.44 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.59240.84 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.60739.34 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.52947.14 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysAll
0.67232.84 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.58541.54 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.71528.53 StarsAngle,Fixed object,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.80919.13 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.51494 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.47852.24 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.21794 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.57542.54 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.53546.54 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.42584 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.44555.54 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.61638.43 StarsAngle,Fixed object,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.60839.24 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.38161.94 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.74625.44 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.023-2.33 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.63536.54 StarsAngleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.51148.94 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.9762.43 StarsAllAllPrincipal Arterial OtherNot specified
0.72827.24 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.86713.33 StarsAngle,Fixed object,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.266-26.63 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.61238.84 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.75724.34 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.086-8.63 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.63836.24 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.54545.54 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.9762.43 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.76423.64 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.67732.33 StarsAngle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.526-52.63 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.58241.84 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.49514 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.26573.54 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.57742.34 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.50649.44 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.46953.14 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.72283 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified

Countermeasure: Install chevron signs and curve warning signs

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.59240.84 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.66343 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.55644.44 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.48951.14 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.69430.64 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.56443.64 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.76423.63 StarsAngle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.463-46.33 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.46453.64 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified

Countermeasure: Install chevron signs on horizontal curves

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9742.63 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.92-923 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.63374 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.40659.44 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysAll
1.271-27.13 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.9103 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.291-29.13 StarsAngle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
1.463-46.33 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.83416.63 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified

Countermeasure: Install chevron signs, curve warning signs, and sequential flashing beacons

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.52447.64 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.23176.94 StarsNighttimeAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.62737.34 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.56443.64 StarsWet roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.47752.34 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.51848.24 StarsRun off roadAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.53346.74 StarsAngle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicleAllPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.61838.24 StarsAllK,A,B,CPrincipal Arterial Other Freeways and ExpresswaysNot specified
0.43856.24 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysNot specified