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                        Low-Cost Treatments for Horizontal Curve Safety 2016


            
            In This Section
        Roadway Departure Safety
                Strategic Approach
                                Strategic Plan
                Crash Emphasis Brochures
                Focused Approach
                Noteworthy Practices
                Partner Resources
                Keep Vehicles on the Road
                                Pavement Friction
                Horizontal Curve Safety
                Rumble Strips and Rumble Stripes
                Nighttime Visibility
                Provide for a Safe Recovery
                                SafetyEdge
                Clear Zones
                Reduce Crash Severity
                                Overview
                Hardware Eligibility Letters
                Focus on Reducing Rural Roadway Departures (FoRRRwD)
                                Overview
                All Public Roads
                Proven Countermeasures
                Systemic Approach
                Safety Action Plans
                FoRRRwD Resources
                
                Appendix A: Low-Cost Safety Improvements in Pennsylvania
Appendix A: Low-Cost Safety Improvements in Pennsylvania

BACKGROUND

A higher percentage of fatal curve-related crashes occur on rural roads–particularly on two-lane rural roads–due largely in part to the predominance of horizontal curves on typical rural roads. In 2013, more than 13 percent of fatal crashes in Pennsylvania occurred due to Curve Driver Error Crashes, many of which involved roadway departures. To address curve-related crashes, the Pennsylvania Department of Transportation (PennDOT) provided guidance to the districts on the implementation of enhanced sign and marking improvements for curves that exhibit a higher than expected crash frequency. PennDOT identified priority curves by examining crash frequency, crash rate, and crash severity.

Photograph of a two-lane roadway with a horizontal curve. A horizontal curve warning sign is supplemented with a speed advisory plaque on the bottom and an orange flag on the top. The signs are installed on the right side of the roadway prior to the curve. Chevrons are also installed along the outside of the curve.

***Figure A-1. Photo. An orange flag supplementing the reverse curve warning sign and speed advisory plaque. Chevrons were also used to delineate the curve.***

PROGRAM DETAILS

Pavement markings in advance of horizontal curves provide additional warning information, and can also be considered at curve locations where signs alone have been shown to be insufficient. Systematic implementation of improvements on curves is taking place throughout Pennsylvania and include one or more of the following strategies:

Oversized fluorescent yellow advance curve warning signs that could be doubled up (i.e., both sides of the roadway), with optional flashing yellow LED solar powered beacons.
	Advanced curve pavement markings including a "SLOW" legend or "XX MPH" advisory speed marking as an alternate. *(NOTE: Since the PennDOT program began, the*NCHRP Report 600*has since been released and contains design guidelines as to which markings are effective in reducing speeds at horizontal curves and which markings are not as effective (p. 20-4)).*
	Correction of any shoulder drop offs within the curve.
	Chevron delineation around the curve.
	Curve widening.PennDOT estimates there have been between 500 to 600 applications of the low-cost safety improvements throughout the State, many of which have been State funded.

RESULTS

PennDOT Districts have found this combination of treatments, when utilized correctly, effectively contributes to combatting curve-related crashes. Data suggests these safety treatments have improved safety on specifically identified horizontal curves. Overall, Curve Driver Error Crashes have fallen from a five-year average of 6,798 in 2007 to 5,060 in 2012. A three-year before/after analysis of locations where a combination of these countermeasures were implemented between 2000 and 2008 resulted in the following:

Decrease in overall crashes from 1,452 to 1,200 (17-percent reduction).
	Decrease in fatal crashes from 27 to 15 (44-percent reduction).
	Decrease in major injury crashes from 65 to 39 (40-percent reduction).When the treatment was first introduced, there were concerns of motorcycles slipping on the paint (2001); but over time, the treatments have become widely accepted and the general public have not voiced any other concerns.

CONSIDERATIONS

PennDOT stresses the importance of sound engineering judgment when selecting the combination of countermeasures for implementation. Additionally, speed limit compliance, geometric features of the curve, sight distance, and traffic volume must be taken into consideration when implementing this treatment. Finally, high friction surface treatment should be considered as another possible countermeasure where wet pavement/curve related crashes occur at a higher rate.

As noted, *NCHRP Report 600* has since been released and contains design guidelines as to which markings are effective in reducing speeds at horizontal curves and which markings are not as effective.

CONTACT INFORMATION

The Traffic and Safety Section of PennDOT provided the information for this case study. Visit http://www.penndot.gov/ for more information. All images are courtesy of PennDOT.
      
  Book traversal links for Appendix A: Low-Cost Safety Improvements in Pennsylvania
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                    Appendix B: Systemic Improvements in Minnesota ›
                
                Book:Low-Cost Treatments for Horizontal Curve Safety 2016
              CHAPTER 1. INTRODUCTION
                CHAPTER 2. THE TWO COMPONENTS OF SAFETY IMPROVEMENT: SITE ANALYIS AND THE SYSTEMIC APPROACH
                CHAPTER 3. MARKINGS
                CHAPTER 4. SIGNS
                CHAPTER 5. PAVEMENT COUNTERMEASURES
                CHAPTER 6. ROADSIDE IMPROVEMENTS
                CHAPTER 7. ADDRESSING INTERSECTIONS IN CURVES
                REFERENCES
                Glossary
                Appendix A: Low-Cost Safety Improvements in Pennsylvania
                Appendix B: Systemic Improvements in Minnesota
                Appendix C: Application of Edge Lines in Missouri
                Appendix D: Upgrading Curve Signing in Ohio
                APPENDIX E: Application Of Sequential Dynamic Curve Warning Systems (SDCWS)
                Appendix F: Application of High Friction Surface Treatment in Kentucky
                Appendix G: Every Day Counts – High Friction Surface Treatments
                Appendix H: Utility Pole Management in New Jersey
                ACRONYMS U.S. DEPARTMENT OF TRANSPORTATION

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