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Publication Number:  FHWA-HRT-14-020    Date:  January 2015
Publication Number: FHWA-HRT-14-020
Date: January 2015

 

Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project

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FOREWORD

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.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

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

6. Performing Organization Code
7. Author(s)

Shauna L. Hallmark, Neal Hawkins, and Omar Smadi

8. Performing Organization Report No.

InTrans Project 08-320

9. Performing Organization Name and Address

Center for Transportation Research and Education
Iowa State University
2711 South Loop Drive, Suite 4700
Ames, IA 50010-8664

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-07-H-00022

12. Sponsoring Agency Name and Address

Office of Infrastructure Research & Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

 

Midwest Transportation Consortium
2711 South Loop Drive, Suite 4700
Ames, IA 50010-8664

Iowa Highway Research Board
Iowa Department of Transportation, Office of Traffic and Safety
800 Lincoln Way
Ames, IA 50010

 

Texas Department of Transportation
125 E. 11th Street
Austin, TX 78701-2483

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

IHRB Project TR-579

15. Supplementary Notes

The Contracting Officer's Technical Representative was Richard Knoblauch.

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.

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.
http://www.ntis.gov

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

206

22. Price

N/A

Form DOT F 1700.7 Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

 

LIST OF FIGURES

Figure 1. Photo. Speed display sign used in study
Figure 2. Photo. Curve (warning) display sign used in study
Figure 3. Chart. Percent of sites experiencing a change in mean speed of a certain magnitude at the PC
Figure 4. Chart. Percent of sites experiencing a change in 85th percentile speed of a certain magnitude at the PC.
Figure 5. Chart. Changes in percent of vehicles traveling 5 or more mph over posted limit or advisory speed at the PC.
Figure 6. Chart. Changes in percent of vehicles traveling 10 or more mph over posted limit or advisory speed at the PC.
Figure 7. Chart. Changes in percent of vehicles traveling 15 or more mph over posted limit or advisory speed at the PC.
Figure 8. Chart. Changes in percent of vehicles traveling 20 or more mph over posted limit or advisory speed at the PC.
Figure 9. Chart. Percent of sites experiencing a change in mean speed of a certain magnitude at the CC.
Figure 10. Chart. Percent of sites experiencing a change in 85th percentile speed of a certain magnitude at the CC
Figure 11. Chart. Changes in percent of vehicles traveling 5 or more mph over posted limit or advisory speed at the CC
Figure 12. Chart. Changes in percent of vehicles traveling 10 or more mph over posted limit or advisory speed at the CC
Figure 13. Chart. Changes in percent of vehicles traveling 15 or more mph over posted limit or advisory speed at the CC.
Figure 14. Chart. Changes in percent of vehicles traveling 20 or more mph over posted limit or advisory speed at the CC
Figure 15. Chart. Changes in mean speed at the PC by sign type about 1 month after sign installation
Figure 16. Chart. Changes in mean speed at the PC by sign type about 12 months after sign installation
Figure 17. Chart. Changes in mean speed at the PC by sign type about 24 months after sign installation
Figure 18. Chart. Changes in 85th percentile speed at the PC by sign type about 1 month after sign installation
Figure 19. Chart. Changes in 85th percentile speed at the PC by sign type about 12months after sign installation.
Figure 20. Chart. Changes in 85th percentile speed at the PC by sign type about 24 months after sign installation.
Figure 21. Chart. Changes in mean speed at the CC by sign type about 1 month after sign installation
Figure 22. Chart. Changes in mean speed at the CC by sign type about 12 months after sign installation
Figure 23. Chart. Changes in mean speed at the CC by sign type about 24 months after sign installation
Figure 24. Chart. Changes in 85th percentile speed at the CC by sign type about 1 months after sign installation.
Figure 25. Chart. Changes in 85th percentile speed at the CC by sign type about 12 monthsafter sign installation.
Figure 26. Chart. Changes in 85th percentile speed at the CC by sign type about 24 months after sign installation.
Figure 27. Photo. Interstate 5 DSFS systems in Oregon (Northbound before).
Figure 28. Photo. Interstate 5 DSFS systems in Oregon (Northbound after).
Figure 29. Photo. Interstate 5 DSFS systems in Oregon (Southbound before).
Figure 30. Photo. Interstate 5 DSFS systems in Oregon (Southbound after).
Figure 31. Photo. DSFS in Norfolk, UK.
Figure 32. Photo. DSFS in Bellevue, WA
Figure 33. Photo. Speed warning sign in the Sacramento River Canyon.
Figure 34. Map. Location of treatment and crash analysis control sites in Arizona.
Figure 35. Map. Location of treatment and crash analysis control sites in Florida
Figure 36. Map. Location of treatment and crash analysis control sites in Iowa
Figure 37. Map. Location of treatment and crash analysis control sites in Franklin County, OH
Figure 38. Map. Location of treatment and crash analysis control sites in Oregon.
Figure 39. Map. Location of treatment and crash analysis control sites in Texas
Figure 40. Map. Location of treatment and crash analysis control sites in Washington
Figure 41. Photo. Types of dynamic speed-activated feedback signs
Figure 42. Illustration. Dynamic speed display
Figure 43. Illustration. Curve warning display
Figure 44. Illustration. Speed data collection locations at each site
Figure 45. Equation. Calculation of mean speed
Figure 46. Equation. z-test
Figure 47. Equation. Percent change in fraction of vehicles exceeding posted/advisory speed after installation of signs.
Figure 48. Chart. Percent of sites experiencing a change in mean speed of a certain magnitude at the PC
Figure 49. Chart. Percent of sites experiencing a change in 85th percentile speed of a certain magnitude at the PC
Figure 50. Chart. Changes in percent of vehicles traveling 5 or more mph over posted limit or advisory speed at the PC.
Figure 51. Chart. Changes in percent of vehicles traveling 10 or more mph over posted limit or advisory speed at the PC
Figure 52. Chart. Changes in percent of vehicles traveling 15 or more mph over posted limit or advisory speed at the PC
Figure 53. Chart. Changes in percent of vehicles traveling 20 or more mph over posted limit or advisory speed at the PC.
Figure 54. Chart. Percent of sites experiencing a change in mean speed of a certain magnitude at the CC.
Figure 55. Chart. Percent of sites experiencing a change in 85th percentile speed of a certain magnitude at the CC.
Figure 56. Chart. Changes in percent of vehicles traveling 5 or more over posted limit or advisory speed at the CC
Figure 57. Chart. Changes in percent of vehicles traveling 10 or more over posted limit or advisory speed at the CC
Figure 58. Chart. Changes in percent of vehicles traveling 15 or more over posted limit or advisory speed at the CC
Figure 59. Chart. Changes in percent of vehicles traveling 20 or more over posted limit or advisory speed at the CC
Figure 60. Chart. Changes in mean speed at the PC by sign type about 1 month after sign installation
Figure 61. Chart. Changes in mean speed at the PC by sign type about 12 months after sign installation
Figure 62. Chart. Changes in mean speed at the PC by sign type about 24 months after sign installation
Figure 63. Chart. Changes in 85th percentile speed at the PC by sign type about 1 month after sign installation.
Figure 64. Chart. Changes in 85th percentile speed at the PC by sign type about 12 months after sign installation.
Figure 65. Chart. Changes in 85th percentile speed at the PC by sign type about 24 months after sign installation.
Figure 66. Chart. Changes in mean speed at the CC by sign type about 1 months after sign installation
Figure 67. Chart. Changes in mean speed at the CC by sign type about 12 months after sign installation.
Figure 68. Chart. Changes in mean speed at the CC by sign type about 24 months after sign installation
Figure 69. Chart. Changes in 85th percentile speed at the CC by sign type 1 month after sign installation
Figure 70. Chart. Changes in 85th percentile speed at the CC by sign type 12 months after sign installation
Figure 71. Chart. Changes in 85th percentile speed at the CC by sign type 24 months after sign installation
Figure 72. Equation. Calculation of crash rate per quarter
Figure 73. Equation. Expression for crash counts across years and sites.
Figure 74. Equation. Model A (ZIP).
Figure 75. Equation. Model B (ZIP)
Figure 76. Equation. CMF calculation.
Figure 77. Equation. Calculation of standard error for the CMF.
Figure 78. Photo. Additional traffic calming installed between 12 and 24 months at SR 95.

 

LIST OF TABLES

Table 1. Average change across sites at the PC
Table 2. Summary of results for individual sites at the PC 1 month after sign installation (part 1).
Table 3. Summary of results for individual sites at the PC 1 month after sign installation (part 2).
Table 4. Summary of results for individual sites at the PC 1 month after sign installation (part 3).
Table 5. Summary of results for individual sites at the PC 12 months after sign installation (part 1).
Table 6. Summary of results for individual sites at the PC 12 months after sign installation (part 2).
Table 7. Summary of results for individual sites at the PC 12 months after sign installation (part 3).
Table 8. Summary of results for individual sites at the PC 24 months after sign installation (part 1).
Table 9. Summary of results for individual sites at the PC 24 months after sign installation (part 2).
Table 10. Summary of results for individual sites at the PC 24 months after sign installation (part 3).
Table 11. Average change across sites at the CC.
Table 12. Summary of results for individual sites at the CC 1 month after sign installation (part 1).
Table 13. Summary of results for individual sites at the CC 1 month after sign installation (part 2).
Table 14. Summary of results for individual sites at the CC 1 month after sign installation (part 3).
Table 15. Summary of results for individual sites at the CC 12 months after sign installation (part 1).
Table 16. Summary of results for individual sites at the CC 12 months after sign installation (part 2).
Table 17. Summary of results for individual sites at the CC 12 months after sign installation (part 3).
Table 18. Summary of results for individual sites at the CC 24 months after sign installation (part 1).
Table 19. Summary of results for individual sites at the CC 24 months after sign installation (part 2).
Table 20. Summary of results for individual sites at the CC 24 months after sign installation (part 3).
Table 21. Decrease in crashes using simple descriptive statistics
Table 22. Results for calculation of crash modification factors for DSFS
Table 23. Advisory messages for Interstate 5 dynamic speed-activated feedback sign system
Table 24. List of final curve sites selected.
Table 25. Sign installation information
Table 26. Counter output
Table 27. Summary of results at the PC 1 month after sign installation (part 1).
Table 28. Summary of results at the PC 1 month after sign installation (part 2).
Table 29. Summary of results at the PC 1 month after sign installation (part 3).
Table 30. Summary of results at the PC 12 months after sign installation (part 1)
Table 31. Summary of results at the PC 12 months after sign installation (part 2)
Table 32. Summary of results at the PC 12 months after sign installation (part 3)
Table 33. Summary of results at the PC 24 months after sign installation (part 1)
Table 34. Summary of results at the PC 24 months after sign installation (part 2)
Table 35. Summary of results at the PC 24 months after sign installation (part 3).
Table 36. Summary of results at the CC 1 month after sign installation (part 1)
Table 37. Summary of results at the CC 1 month after sign installation (part 2)
Table 38. Summary of results at the CC 1 month after sign installation (part 3)
Table 39. Summary of results for the CC 12 months after sign installation (part 1).
Table 40. Summary of results for the CC 12 months after sign installation (part 2).
Table 41. Summary of results for the CC 12 months after sign installation (part 3).
Table 42. Summary of results at the CC 24 months after sign installation (part 1).
Table 43. Summary of results at the CC 24 months after sign installation (part 2).
Table 44. Summary of results at the CC 24 months after sign installation (part 3).
Table 45. Average change over sites at PC.
Table 46. Average change over sites at CC
Table 47. Description of covariates
Table 48. Simple before and after comparison of crashes for both directions.
Table 49. Simple before and after comparison of crashes for one direction
Table 50. Parameter estimations for ZIP model for total crashes in both directions
Table 51. Parameter estimations for ZIP model for total crashes in one direction.
Table 52. Parameter estimations for ZIP model for SV crashes in both directions
Table 53. Parameter estimations for ZIP model for SV crashes in one direction.
Table 54. Results for calculation of crash modification factors
Table 55. Results for Arizona: SR 377 at 0.5 miles upstream (SB)
Table 56. Results for Arizona: SR 377 at the PC (SB).
Table 57. Results for Arizona: SR 377 at the CC (SB)
Table 58. Results for Arizona: SR 95 at 0.5 miles upstream (SB)
Table 59. Results for Arizona: SR 95 at the PC (SB)
Table 60. Results for Arizona: SR 95 at the CC (SB)
Table 61. Results for Florida: SR 267 upstream of curve (SB)
Table 62. Results for Florida: SR 267 at the PC (SB)
Table 63. Results for Florida: SR 267 at the CC (SB).
Table 64. Results for Florida: US 20 by Tallahassee upstream of curve (WB).
Table 65. Results for Florida: US 20 by Tallahassee at the PC (WB).
Table 66. Results for Florida: US 20 by Tallahassee at the CC (WB).
Table 67. Results for Florida: US 20 Gainesville upstream of curve (EB).
Table 68. Results for Florida: US 20 Gainesville at the PC (EB).
Table 69. Results for Florida: US 20 Gainesville at the CC (EB)
Table 70. Results for Iowa: US 30 upstream (EB)
Table 71. Results for Iowa: US 30 at the PC (EB)
Table 72. Results for Iowa: US 30 at the CC (EB)
Table 73. Results for Iowa: US 67 upstream (SB).
Table 74. Results for Iowa: US 67 at the PC (SB).
Table 75. Results for Iowa: US 67 at the CC (SB).
Table 76. Results for Iowa: US 69 upstream (NB).
Table 77. Results for Iowa: US 69 the PC (NB).
Table 78. Results for Iowa: US 69 at the CC (NB).
Table 79. Results for Iowa: Iowa 136 upstream (NB).
Table 80. Results for Iowa: Iowa 136 at the PC (NB).
Table 81. Results for Iowa: Iowa 136 at the CC (NB).
Table 82. Results for Ohio: Alkire Road upstream of curve (EB).
Table 83. Results for Ohio: Alkire Road at the PC (EB).
Table 84. Results for Ohio: Alkire Road at the CC (EB)
Table 85. Results for Ohio: Norton Road upstream of curve (SB).
Table 86. Results for Ohio: Norton Road at the PC (SB).
Table 87. Results for Ohio: Norton Road at the CC (SB)
Table 88. Results for Ohio: Pontius Road upstream of curve (SB).
Table 89. Results for Ohio: Pontius Road at the PC (SB)
Table 90. Results for Ohio: Pontius Road at the CC (SB).
Table 91. Results for Oregon: OR 42 upstream of curve (WB).
Table 92. Results for Oregon: OR 42 at the PC (WB).
Table 93. Results for Oregon: OR 42 at the CC (WB)
Table 94. Results for Oregon: OR 238 upstream of curve (EB).
Table 95. Results for Oregon: OR 238 at the PC (EB)
Table 96. Results for Oregon: OR 238 at the CC (EB)
Table 97. Results for Oregon: US 101 upstream of curve (SB)
Table 98. Results for Oregon: US 101 at the PC (SB).
Table 99. Results for Oregon: US 101 at the CC (SB)
Table 100. Results for Oregon: OR 126 upstream of curve (EB).
Table 101. Results for Oregon: OR 126 at the PC (EB)
Table 102. Results for Oregon: OR 126 at the CC (EB)
Table 103. Results for Texas: FM 481 upstream of curve (EB).
Table 104. Results for Texas: FM 481 at the PC (EB)
Table 105. Results for Texas: FM 481 at the CC (EB)
Table 106. Results for Texas: FM 755 upstream of curve (WB).
Table 107. Results for Texas: FM 755 at the PC (WB).
Table 108. Results for Texas: FM 755 at the CC (WB)
Table 109. Results for Texas: SH 359 upstream of curve (WB)
Table 110. Results for Texas: SH 359 at the PC (WB)
Table 111. Results for Texas: SH 359 at the CC (WB)
Table 112. Results for Texas: US 90 upstream of curve (EB).
Table 113. Results for Texas: US 90 at the PC (EB).
Table 114. Results for Texas: US 90 at the CC (EB).
Table 115. Results for Washington: US 101 upstream of curve (EB).
Table 116. Results for Washington: US 101 at the PC (EB)
Table 117. Results for Washington: US 101 at the CC (EB).
Table 118. Results for Washington: SR 7 upstream of curve (EB).
Table 119. Results for Washington: SR 7 at the PC (EB)
Table 120. Results for Washington: SR 7 at the CC (EB).
Table 121. Comparison of speed changes daytime versus nighttime for Washington US 101
Table 122. Comparison of speed changes for daytime versus nighttime for Washington US 101
Table 123. Comparison of speed changes daytime versus nighttime for Washington SR 7
Table 124. Comparison of speed changes for daytime versus nighttime for Washington SR 7.
Table 125. Comparison of speed changes daytime versus nighttime for Arizona SR 95.
Table 126. Comparison of speed changes for daytime changes versus nighttime changes for Arizona SR 95
Table 127. Comparison of speed changes daytime versus nighttime for Arizona SR 377.
Table 128.Comparison of speed changes for daytime changes versus nighttime changes for Arizona SR 377.
Table 129. Comparison of speed changes daytime versus nighttime for Florida SR 20-Gainesville
Table 130. Comparison of speed changes for daytime changes versus nighttime changes for Florida SR 20-Gainesville
Table 131. Comparison of speed changes daytime versus nighttime for Florida SR 267.
Table 132. Comparison of speed changes for daytime changes versus nighttime changes for Florida SR 267
Table 133. Comparison of speed changes daytime versus nighttime for Florida SR 20 - Tallahassee
Table 134. Comparison of speed changes for daytime changes versus nighttime changes for Florida SR 20-Tallahassee
Table 135. Speed changes for Washington SR 7 PC by heavy truck versus passenger vehicle
Table 136. Speed changes for Washington US 101 PC by heavy truck versus passenger vehicle
Table 137. Speed changes for Oregon OR 238 PC by heavy truck versus passenger vehicle
Table 138. Speed changes for Oregon US 101 PC by heavy truck versus passenger vehicle
Table 139. Speed changes for Oregon OR 42 PC by heavy truck versus passenger vehicle

 

LIST OF ACRONYMS AND ABBREVIATIONS

 

AADTAnnual Average Daily Traffic
ADTAverage Daily Traffic
CaltransCalifornia Department of Transportation
CCCenter of Curve
CIConfidence Interval
CMFCrash Modification Factor
CTRECenter for Transportation Research and Education
DSFSDynamic Speed Feedback Sign
EBEastbound
EB approachEmpirical Bayes approach
FARSFatality Analysis Reporting System
FBFull Bayesian
FHWAFederal Highway Administration
HSISHighway Safety Information System
Iowa DOTIowa Department of Transportation
LEDLight-Emitting Diode
mphMiles Per Hour
MUTCDManual on Uniform Traffic Control Devices
NBNorthbound
PCPoint of Curvature
SBSouthbound
SDStandard Deviation
SPFSafety Performance Function
STDEStandard Error
SVSingle-Vehicle
vpdVehicles per Day
WBWestbound

 

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