U.S. Department of Transportation
Federal Highway Administration
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Washington, DC 20590
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
| REPORT |
| This report is an archived publication and may contain dated technical, contact, and link information |
 |
| Publication Number: FHWA-HRT-14-020 Date: January 2015 |
Publication Number: FHWA-HRT-14-020 Date: January 2015 |
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The overall goal of the Federal Highway Administration's (FHWA) Speed Management Program is to improve the safety of the Nation's highways through the reduction of speeding and speed-related crashes. Drivers who exceed the speed limit or drive too fast for ambient conditions are involved in nearly one-third of all fatal crashes. Each year, more than 13,000 people are killed in speeding-related crashes. The majority of speeding-related crashes occur on roads that are not part of the interstate system. Local streets and collector roads have the highest speeding-related fatality rate on a per vehicle miles driven basis. The challenge facing the safety professional is to design roadways so that drivers better understand the nature of the roadway and adjust their speed appropriately. Design guidance is needed so that roadways are designed and/or retrofitted to induce drivers to drive at more appropriate speeds.
This report discusses treatments that can potentially reduce speeds and speeding-related crash risks on rural horizontal curves. This report describes the effectiveness of dynamic signs that alert drivers to changes in roadway conditions and that provide those drivers with recommended speeds to safely negotiate a curve. The effectiveness of these signs were determined based on field analysis in 22 locations.
Monique R. Evans
Director, Office of Safety
Research and Development
Notice
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.
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Technical Report Documentation Page
| 1. Report No.
FHWA-HRT-14-020 |
2. Government Accession No. | 3 Recipient's Catalog No. | ||||
| 4. Title and Subtitle
Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project |
5. Report Date January 2015 |
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| 6. Performing Organization Code | ||||||
| 7. Author(s)
Shauna L. Hallmark, Neal Hawkins, and Omar Smadi |
8. Performing Organization Report No. InTrans Project 08-320 |
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9. Performing Organization Name and Address Center for Transportation Research and Education |
10. Work Unit No. (TRAIS) |
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| 11. Contract or Grant No. DTFH61-07-H-00022 |
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12. Sponsoring Agency Name and Address
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13. Type of Report and Period Covered Final Report |
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14. Sponsoring Agency Code IHRB Project TR-579 |
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| 15. Supplementary Notes The Contracting Officer's Technical Representative was Richard Knoblauch. |
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| 16. Abstract
Lane departure crashes are a significant safety concern. The majority of lane departure crashes occur on rural two-lane roadways, with a disproportionate number of these crashes on horizontal curves. Curve-related crashes involve a number of roadway and driver causative factors. A primary driver factor is speeding.
Dynamic speed feedback sign (DSFS) systems are one method to reduce vehicle speeds and, consequently, crashes on curves. These systems show promise but they have not been fully evaluated on curves. The Center for Transportation Research and Education at Iowa State University conducted a national demonstration project to evaluate the effectiveness of two different DSFSs in reducing speed and crashes on curves at 22 total sites on rural two-lane roadways in seven States. The goal is to provide traffic safety engineers and other professionals with additional tools to manage speeds and crashes on rural horizontal curves more effectively.
Data were collected before and at 1, 12, and 24 months after installation of the DSFS. On average, most sites had decreases in mean speeds, with decreases up to 10.9 miles per hour (mph) noted for both the point of curvature (PC) and center of curve (CC). Most sites experienced changes in 85th percentile speed of 3 mph or more at the PC, with the majority of sites having a decrease of 2 mph at the CC. The numbers of vehicles traveling 5, 10, 15, or 20 mph over the posted or advisory speed limit were also compared. Large reductions in the number of vehicles traveling over the posted or advisory speed occurred for all of the after periods at the PC and CC, indicating that the signs were effective in reducing high-end speeds, as well as average and 85th percentile speeds.
A before-and-after crash analysis was also conducted, and crash modification factors (CMF) were developed. CMFs ranged from 0.93 to 0.95 depending on the crash type and direction of the crash. |
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| 17. Key Words
crash mitigation, curve speed safety, horizontal curves, lane position, low-cost safety improvements, rural road safety, speed-activated displays, speed warning signs |
18. Distribution Statement
No restrictions. This document is available to the public through NTIS: National Technical Information Service, Springfield, VA 22161. |
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19. Security Classification Unclassified |
20. Security Classification Unclassified |
21. No. of Pages 206 |
22. Price N/A |
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| Form DOT F 1700.7 | Reproduction of completed page authorized |
SI* (Modern Metric) Conversion Factors
| AADT | Annual Average Daily Traffic |
| ADT | Average Daily Traffic |
| Caltrans | California Department of Transportation |
| CC | Center of Curve |
| CI | Confidence Interval |
| CMF | Crash Modification Factor |
| CTRE | Center for Transportation Research and Education |
| DSFS | Dynamic Speed Feedback Sign |
| EB | Eastbound |
| EB approach | Empirical Bayes approach |
| FARS | Fatality Analysis Reporting System |
| FB | Full Bayesian |
| FHWA | Federal Highway Administration |
| HSIS | Highway Safety Information System |
| Iowa DOT | Iowa Department of Transportation |
| LED | Light-Emitting Diode |
| mph | Miles Per Hour |
| MUTCD | Manual on Uniform Traffic Control Devices |
| NB | Northbound |
| PC | Point of Curvature |
| SB | Southbound |
| SD | Standard Deviation |
| SPF | Safety Performance Function |
| STDE | Standard Error |
| SV | Single-Vehicle |
| vpd | Vehicles per Day |
| WB | Westbound |
