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(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.606 39.4 4 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.592 40.8 3 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.607 39.3 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.529 47.1 3 Stars Wet road All Principal Arterial Other Freeways and Expressways All
0.672 32.8 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.585 41.5 4 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.715 28.5 3 Stars Angle,Fixed object,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
0.809 19.1 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.51 49 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified
0.478 52.2 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.21 79 3 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.575 42.5 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.535 46.5 3 Stars Wet road All Principal Arterial Other Freeways and Expressways Not specified
0.42 58 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.445 55.5 3 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.616 38.4 3 Stars Angle,Fixed object,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
0.608 39.2 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.381 61.9 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified
0.746 25.4 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
1.023 -2.3 2 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.635 36.5 3 Stars Angle All Principal Arterial Other Freeways and Expressways Not specified
0.511 48.9 3 Stars Wet road All Principal Arterial Other Freeways and Expressways Not specified
0.976 2.4 3 Stars All All Principal Arterial Other Not specified
0.728 27.2 3 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.867 13.3 2 Stars Angle,Fixed object,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
1.266 -26.6 2 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.612 38.8 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified
0.757 24.3 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
1.086 -8.6 2 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.638 36.2 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.545 45.5 3 Stars Wet road All Principal Arterial Other Freeways and Expressways Not specified
0.976 2.4 2 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.764 23.6 3 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.677 32.3 2 Stars Angle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
1.526 -52.6 2 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.582 41.8 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified
0.49 51 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.265 73.5 3 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.577 42.3 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.506 49.4 3 Stars Wet road All Principal Arterial Other Freeways and Expressways Not specified
0.469 53.1 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.72 28 3 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.72 28 3 Stars Angle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
0.568 43.2 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.43 57 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified

Countermeasure: Install chevron signs and curve warning signs

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.592 40.8 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.66 34 3 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.556 44.4 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.489 51.1 3 Stars Wet road All Principal Arterial Other Freeways and Expressways Not specified
0.694 30.6 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.564 43.6 3 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.764 23.6 2 Stars Angle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
1.463 -46.3 2 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.464 53.6 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified

Countermeasure: Install chevron signs on horizontal curves

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.974 2.6 2 Stars All All Principal Arterial Other Freeways and Expressways Not specified
1.92 -92 2 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.63 37 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.406 59.4 3 Stars Wet road All Principal Arterial Other Freeways and Expressways All
1.271 -27.1 2 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.9 10 2 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
1.291 -29.1 2 Stars Angle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
1.463 -46.3 2 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.834 16.6 2 Stars All O Principal Arterial Other Freeways and Expressways Not specified

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.524 47.6 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.231 76.9 3 Stars Nighttime All Principal Arterial Other Freeways and Expressways Not specified
0.627 37.3 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.564 43.6 3 Stars Wet road All Principal Arterial Other Freeways and Expressways Not specified
0.477 52.3 3 Stars All All Principal Arterial Other Freeways and Expressways Not specified
0.518 48.2 3 Stars Run off road All Principal Arterial Other Freeways and Expressways Not specified
0.533 46.7 3 Stars Angle,Fixed object,Frontal and opposing direction sideswipe,Head on,Rear end,Rear to rear,Sideswipe,Single vehicle All Principal Arterial Other Freeways and Expressways Not specified
0.618 38.2 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Not specified
0.438 56.2 3 Stars All O Principal Arterial Other Freeways and Expressways Not specified