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This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-15-030    Date:  May 2015
Publication Number: FHWA-HRT-15-030
Date: May 2015

 

Factors Influencing Operating Speeds and Safety on Rural and Suburban Roads

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FOREWORD

The overall goal of the Federal Highway Administration's 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 the 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 collectors 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 documents the component factors affecting speed and safety on rural and suburban roadways that are not limited access. The report also describes the treatments that have the potential to reduce speed-related crashes.

Monique 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-15-030

2. Government Accession No.

 

3. Recipient's Catalog No.

 

4. Title and Subtitle

Factors Influencing Operating Speeds and Safety on Rural and Suburban Roads

5. Report Date

May 2015

6. Performing Organization Code

N/A

7. Author(s)

Leverson Boodlal, P.E; Eric T. Donnell, Ph.D., P.E; Richard J. Porter, Ph.D., P.E; Dileep Garimella; Thanh Le; Kevin Croshaw; Scott Himes, Ph.D.; Philip Kulis; Jonathan Wood

8. Performing Organization Report No.

N/A

9. Performing Organization Name and Address

10. Work Unit No. (TRAIS)

N/A

KLS Engineering, LLC
45155 Research Pl,
Suite 200
Ashburn, VA 20147

Thomas D. Larson Pennsylvania Transportation Institute
The Pennsylvania State University
201 Transportation Research Bldg
University Park, PA 16802

University of Utah
201 Presidents Circle
Room 201
Salt Lake City, UT 84112

11. Contract or Grant No.

DFTH61-10-C-00057

12. Sponsoring Agency Name and Address

Federal Highway Administration
Turner-Fairbank Highway Research Center
Office of Safety Research and Development
6300 Georgetown Pike, Room T-303, McLean, VA 22101

13. Type of Report and Period Covered

Final Report: September 2010–July 2014

14. Sponsoring Agency Code

15. Supplementary Notes

FHWA COTR: Clayton Chen and Abdul Zineddin, Office of Safety Research and Development

16. Abstract

The objective of this project was to develop a technical report that describes treatments that result in driver self-selection of appropriate operational speeds on curve and tangent sections. The study was conducted in two phases. The first phase included a review of literature on design features and current practices associated with safer operating speeds and identification of treatments for field evaluations. The second phase involved evaluating treatments to determine their effectiveness in reducing speeds on two-lane horizontal curves in rural and suburban areas. High-friction surface treatment was evaluated at four treatment sites and three control sites in West Virginia. The speed and encroachment analyses found no consistent differences between the before and after time periods. The friction analysis, however, clearly demonstrated that the friction supply increased. Optical speed bars (OSB) were implemented and evaluated at seven sites in Massachusetts, four sites in Arizona, and eight sites in Alabama. Two different designs were tested as part of this research, and the results yielded inconsistent speed reductions at all the test sites. Based on the results, it can be concluded that the OSB designs used in this research were unsuccessful in reducing vehicle speeds. The safety effects of lane-width–shoulder-width combinations on rural two-lane, two-way road segments in Minnesota and Illinois were also estimated as part of this study. Parameters for lane width indicators showed that, with shoulder width ignored, the expected number of total (i.e., all types and severities) crashes increases as lane width decreases, but it is difficult to distinguish the performance of an 11-ft lane width from that of a 12-ft lane width. The main effect of shoulder width was a decrease in the expected number of crashes as shoulder width increased. In addition, the interaction of the lane width indicator and shoulder width showed that shoulder width has the greatest effect on safety when the lane width equals 10 ft. Shoulder width also has a greater effect on safety when the lane width is 11 ft than when the lane width is 12 ft.

17. Key Words

Horizontal curves, speeding related crashes, high friction surface treatment, optical speed bars, lane-width–shoulder-width combinations

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 Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

376

22. Price

N/A

Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

LIST OF FIGURES

Figure 1. Graph. Approximate relationships between design and running speeds for urban conditions (figure 1 from Porter et al., 2012)
Figure 2. Graph. Comparison of maximum side friction factor used for design to available side friction (figure 2 from Porter et al., 2012)
Figure 3. Graph. Comparison of minimum curve radius used for design to minimum curve radii (figure 3 from Porter et al., 2012)
Figure 4. Graph. Maximum side friction factor assumed for design (figure 3-6 from AASHTO 2011)
Figure 5. Equation. Minimum radius of horizontal curvature
Figure 6. Equation. Required side friction factor
Figure 7. Chart. Observed speed-related outcomes of the typical U.S. design practice (figure 2a from Donnell et al., 2009)
Figure 8. Graph. Observed relationships between design speed and operating speeds (figure 5 from Porter et al., 2012)
Figure 9. Diagram. Conceptual speed-related outcomes of U.S. road design practice (adapted from figure 1 in Tarris et al., 2000)
Figure 10. Graph. Relationship between change in travel speed during a crash and the probability of fatality (plotted model estimated by Joksch)
Figure 11. Graph. CMFs for combinations of lane and shoulder widths for two-lane rural highways (Average Annual Daily Traffic > 2,000 vehicles/day)
Figure 12. Graph. CMFs for combinations of lane and shoulder widths for two-lane rural highways (figure 1 in Gross et al., 2009)
Figure 13. Graph. Relationships among horizontal curve radius, speed, and safety for two-lane rural highways
Figure 14. Graph. Relationship between lane width and speed and safety for two-lane rural highways
Figure 15. Graph. Relationship between shoulder width and speed and safety for rural two-lane highways
Figure 16. Photo. Photograph of a horizontal curve without the HFST
Figure 17. Photo. Photograph of a horizontal curve with the HFST
Figure 18. Diagram. Location of traffic sensors for treatment and control sites (not to scale)
Figure 19. Equation. Minimum number of measured speeds
Figure 20. Equation. Sum of the sample in before-after comparison groups
Figure 21. Equation. t-statistic to test for the difference between two sample means at each study site
Figure 22. Equation. Percentage of speeding vehicles
Figure 23. Equation. Percent reduction of speeding vehicles.
Figure 24. Equation. Z-statistic to determine the speed difference between a pair of before and after periods
Figure 25. Equation. Combined proportion of vehicles speeding during the before and after data-collection periods.
Figure 26. Equation. F-test to compare the speed variance in the before and after periods.
Figure 27. Equation Proportion of vehicles encroaching on the edge line or centerline.
Figure 28. Equation. Z-statistic to determine the proportion of vehicles encroaching on a lane line during the before and after data-collection periods
Figure 29. Equation. Combined proportion of vehicles encroaching on a lane line between the before and after data-collection periods
Figure 30. Photo. Dynamic friction tester
Figure 31. Graph. Road friction curves (for illustrative purposes only)
Figure 32. Equation. Side friction demand
Figure 33. Diagram. Geometric layout of WV Route 32 treatment site (not to scale)
Figure 34. Graph. Graphical representation of speeds at the WV Route 32 treatment site.
Figure 35. Diagram. Geometric layout of the WV Route 32 comparison site (not to scale)
Figure 36. Graph. Graphical representation of speeds at the WV Route 32 comparison site
Figure 37. Diagram. Geometric layout of the U.S. Route 33 treatment site (not to scale)
Figure 38. Graph. Graphical representation of speeds at the U.S. Route 33 treatment site
Figure 39. Diagram. Geometric layout of the U.S. Route 33 comparison site (not to scale)
Figure 40. Graph. Graphical representation of speeds at the U.S. Route 33 comparison site
Figure 41. Diagram. Geometric layout of the U.S. Route 219 treatment A site (not to scale).
Figure 42. Graph. Graphical representation of speeds at the U.S. Route 219 treatment A site
Figure 43. Diagram. Geometric layout of the U.S. Route 219 treatment B site (not to scale)
Figure 44. Graph. Graphical representation of speeds at the U.S. Route 219 treatment B site.
Figure 45. Diagram. Geometric layout of the U.S. Route 219 comparison site (not to scale)
Figure 46. Graph. Graphical representation of speeds at the U.S. Route 219 comparison site
Figure 47. Graph. WV Route 32 treatment site operating speeds (PSL = 55 mph)
Figure 48. Graph. WV Route 32 comparison site operating speeds (PSL = 55 mph)
Figure 49. Graph. U.S. Route 33 treatment site operating speeds (PSL = 55 mph)
Figure 50. Graph. U.S. Route 33 comparison site operating speeds (PSL = 55 mph)
Figure 51. Graph. U.S. Route 219 treatment site A (MM 6.32) operating speeds (PSL = 55 mph)
Figure 52. Graph. U.S. Route 219 treatment site B (MM 5.81) operating speeds (PSL=55 mph)
Figure 53. Graph. U.S. Route 219 comparison site operating speeds (PSL = 55 mph)
Figure 54. Graph. Side friction supply before and after for WV Route 32 sites.
Figure 55. Graph. Side friction supply before and after for U.S. Route 33 sites
Figure 56. Graph. Side friction supply before and after for U.S. Route 219 sites
Figure 57. Equation. Side friction demand
Figure 58. Photo. OSB example
Figure 59. Equation. Length of OSB treatment
Figure 60. Equation. Individual placement of the OSBs
Figure 61. Diagram. OSB data-collection setup (not to scale)
Figure 62. Diagram. Geometric layout of northbound Pierce Ferry Road (not to scale)
Figure 63. Graph. Graphical representation of speeds on northbound Pierce Ferry Road.
Figure 64. Diagram. Geometric layout of southbound Shinarump Road (not to scale)
Figure 65. Graph. Graphical representation of speeds on southbound Shinarump Road.
Figure 66. Diagram. Geometric layout of southbound Diamond Bar Road in the before
Figure 67. Diagram. Geometric layout of southbound Diamond Bar Road in the after periods (not to scale)
Figure 68. Graph. Graphical representation of speeds on southbound Diamond Bar Road.
Figure 69. Diagram. Geometric layout of southbound County Route 1 (not to scale)
Figure 70. Graph. Graphical representation of speeds on southbound County Route 1
Figure 71. Diagram. Geometric layout of Alabama Location #1 (not to scale)
Figure 72. Graph. Graphical representation of speeds at Alabama Location #1
Figure 73. Diagram. Geometric layout of Alabama Location #2 (not to scale)
Figure 74. Graph. Graphical representation of speeds at Alabama Location #2
Figure 75. Diagram. Geometric layout of Alabama Location #3 (not to scale)
Figure 76. Graph. Graphical representation of speeds at Alabama Location #3
Figure 77. Diagram. Geometric layout of Alabama Location #4 (not to scale)
Figure 78. Graph. Graphical representation of speeds at Alabama Location #4
Figure 79. Diagram. Geometric layout of Alabama Location #5 (not to scale)
Figure 80. Graph. Graphical representation of speeds at Alabama Location #5
Figure 81. Diagram. Geometric layout of Alabama Location #6 (not to scale)
Figure 82. Graph. Graphical representation of speeds at Alabama Location #6
Figure 83. Diagram. Geometric layout of Alabama Location #7 (not to scale)
Figure 84. Graph. Graphical representation of speeds at Alabama Location #7
Figure 85. Diagram. Geometric layout of Alabama Location #8 (not to scale)
Figure 86. Graph. Graphical representation of speeds at Alabama Location #8
Figure 87. Diagram. Geometric layout of southbound Tucker Road (not to scale)
Figure 88. Graph. Graphical representation of speeds on southbound Tucker Road.
Figure 89. Diagram. Geometric layout of northbound Tucker Road (not to scale)
Figure 90. Graph. Graphical representation of speeds on northbound Tucker Road
Figure 91. Diagram. Geometric layout of southbound Reed Road (not to scale)
Figure 92. Graph. Graphical representation of speeds on southbound Reed Road
Figure 93. Diagram. Geometric layout of southbound New Boston Road (not to scale)
Figure 94. Graph. Graphical representation of speeds on southbound New Boston Road
Figure 95. Diagram. Geometric layout of northbound New Boston Road (not to scale)
Figure 96. Graph. Graphical representation of speeds on northbound New Boston Road
Figure 97. Diagram. Geometric layout of southbound Braley Hill Road (not to scale)
Figure 98. Graph. Graphical representation of speeds on southbound Braley Hill Road
Figure 99. Diagram. Geometric layout of northbound Braley Hill Road (not to scale)
Figure 100. Graph. Graphical representation of speeds on northbound Braley Hill Road
Figure 101. Graph. Operating speeds comparison on northbound Pierce Ferry Road (PSL = 55 mph)
Figure 102. Graph. Operating speeds comparison on southbound Shinarump Road (PSL = 45 mph)
Figure 103. Graph. Operating speeds comparison on southbound Diamond Bar Road (PSL = 45 mph)
Figure 104. Graph. Operating speeds comparison on southbound County Route 1 (PSL = 35 mph)
Figure 105. Graph. Operating speeds comparison at Alabama Location #1 (PSL = 55 mph)
Figure 106. Graph. Operating speeds comparison at Alabama Location #2 (PSL = 55 mph)
Figure 107. Graph. Operating speeds comparison at Alabama Location #3 (PSL = 55 mph)
Figure 108. Graph. Operating speeds comparison at Alabama Location #4 (PSL = 35 mph)
Figure 109. Graph. Operating speeds comparison at Alabama Location #5 (PSL = 40 mph)
Figure 110. Graph. Operating speeds comparison at Alabama Location #6 (PSL = 40 mph)
Figure 111. Graph. Operating speeds comparison at Alabama Location #7 (PSL = 35 mph)
Figure 112. Graph. Operating speeds comparison at Alabama Location #8 (PSL = 35 mph)
Figure 113. Graph. Operating speeds comparison at southbound Tucker Road (PSL = 30 mph)
Figure 114. Graph. Operating speeds comparison at northbound Tucker Road (PSL = 35 mph)
Figure 115. Graph. Operating speeds comparison at southbound Reed Road (PSL = 25 mph)
Figure 116. Graph. Operating speeds comparison on southbound New Boston Road (PSL = 35 mph)
Figure 117. Graph. Operating speeds comparison on northbound New Boston Road (PSL = 35 mph)
Figure 118. Graph. Operating speeds comparison at southbound Braley Hill Road (PSL = 30 mph)
Figure 119. Graph. Operating speeds comparison at northbound Braley Hill Road (PSL = 40 mph)
Figure 120. Chart. Location information in Minnesota’s HSIS Roadway File.
Figure 121. Chart. Location information of the roadway segment in GIS File (Minnesota)
Figure 122. Photo. Locate and mark the point of interest in Google Earth™ using its coordinates (Minnesota)
Figure 123. Chart. Location information in Illinois HSIS Roadway data file.
Figure 124. Equation. Reference point milepost
Figure 125. Equation. Reference point milepost by reversing the direction of increasing station.
Figure 126. Chart. Location information of the roadway segment in GIS file (Illinois)
Figure 127. Chart. Identify coordinate information associated with the roadway segment (Illinois)
Figure 128. Photo. Locate and mark the roadway segment in Google Earth™ with its coordinates
Figure 129. Photo. Measurement of cross-section features in Google Earth™
Figure 130. Photo. Conceptual illustration of calculating lane
Figure 131. Photo. Visual checks of cross-section features in Google Street View™
Figure 132. Photo. Screenshot of estimating deflection angles in Google Earth™
Figure 133. Equation. Smallest distance between PI and all points along the curve
Figure 134. Equation. Curve radius
Figure 135. Equation. Length of the curve
Figure 136. Equation. Expected number of crashes of type i on segment j
Figure 137. Equation. Variance of crashes of type i on segment j
Figure 138. Equation. Probability of accident n with severity i
Figure 139. Graph. CMFs for lane-width–shoulder-width combinations developed directly from regression model parameters, total crashes (all types and severities) on rural, two-lane roads (developed from model estimation results in table 104)
Figure 140. Graph. CMFs for lane-width–shoulder-width combinations developed directly from regression model parameters, fatal-plus-injury crashes (all types) on rural, two-lane roads (developed from model estimation results in table 105)
Figure 141. Photo. Speed table
Figure 142. Photo. Lateral shift
Figure 143. Photo. Speed kidney
Figure 144. Photo. Tubular channelizers
Figure 145. Photo. Transverse rumble strips
Figure 146. Photo. Longitudinal rumble strips
Figure 147. Photo. Converging chevron marking pattern
Figure 148. Equation. Decreasing velocity linear equation
Figure 149. Photo. Transverse markings
Figure 150. Photo. Optical speed bars
Figure 151. Illustration. Peripheral Design (2009 MUTCD, Part 3B. 22)
Figure 152. Illustration. Peripheral Design Variation, Mohave County, AZ
Figure 153. Photo. OSB Variation, Iowa State University
Figure 154. Photo. Speed limit pavement legend
Figure 155. Photo. Enhanced speed limit legend with colored surfacing
Figure 156. Photo. Slow pavement legend
Figure 157. Photo. Zigzag pavement markings
Figure 158. Photo. Painted medians
Figure 159. Photo. Add shoulder markings to narrow lane
Figure 160. Photo. Add centerline and edge line
Figure 161. Photo. Speed feedback sign
Figure 162. Photo. Speed-activated warning sign
Figure 163. Photo. Speed-activated speed limit reminder sign
Figure 164. Photo. Variable speed limit sign
Figure 165. Photo. Transverse pavement markings with speed feedback sign
Figure 166. Photo. Advisory speed limit sign
Figure 167. Photo. Red border speed limit sign
Figure 168. Photo. One-direction large arrow (W1-6) sign
Figure 169. Photo. Add flashers to existing curve warning sign
Figure 170. Photo. Curve warning sign with flags
Figure 171. Photo. Combination horizontal alignment/advisory sign
Figure 172. Photo. Chevron sign
Figure 173. Curve warning sign and chevron sign and flashing beacons
Figure 174. Photo. Curve warning sign and chevron sign
Figure 175. Photo. Delineator post
Figure 176. Photo. Median barriers
Figure 177. Photo. Roadside barriers
Figure 178. Photo. Lane widening
Figure 179. Photo. Two-way left-turn lane
Figure 180. Photo. Additional lane
Figure 181. Photo. Paving shoulder
Figure 182. Photo. Road surface
Figure 183. Photo. Gateway treatment

LIST OF TABLES

Table 1. Quantifiable characteristics of land use contexts (PennDOT and NJDOT, 2008)
Table 2. Relationship between design speed and average running speed (table 3-6 in AASHTO 2011)
Table 3. Minimum radii and superelevation for low-speed urban streets (part of figure 3-13b from AASHTO 2011)
Table 4. Results of iterative inferred design speed calculations
Table 5. Statistical associations between vehicle operating speeds and geometric design features. (Information gathered from TRB Operational Effects of Geometrics Committee, 2011)
Table 6. West Virginia HFST site characteristics
Table 7. Sample size determination
Table 8. Sample size estimates for comparative research
Table 9. WV Route 32 treatment site before data
Table 10. WV Route 32 treatment site friction
Table 11. WV Route 32 comparison site before data
Table 12. WV Route 32 comparison site friction data
Table 13. U.S. Route 33 treatment site before data
Table 14. U.S. Route 33 treatment site friction data
Table 15. U.S. Route 33 comparison site before data
Table 16. U.S. Route 33 comparison site friction data
Table 17. U.S. Route 219 treatment A site before data
Table 18. U.S. Route 219 treatment A site friction data
Table 19. U.S. Route 219 treatment B site before
Table 20. U.S. Route 219 treatment B site friction data
Table 21. U.S. Route 219 comparison site before data
Table 22. U.S. Route 219 comparison site friction data
Table 23. Operating speeds at WV Route 32 sites before and after treatment
Table 24. Operating speeds at U.S. Route 33 before and after treatment
Table 25. Operating speeds at U.S. Route 219 before and after
Table 26. Change in speed from PC to curve midpoint
Table 27. Number of vehicles exceeding the PSL by site
Table 28. Number of vehicles exceeding the advisory speed by site
Table 29. Change in standard deviation of
Table 30. Number of encroachments and braking vehicles by
Table 31. SN65 friction data from the before period
Table 32. SN65 friction data from the immediate after period
Table 33. SN65 friction data from the second after period
Table 34. Before and after friction data for comparison
Table 35. SN65 estimated available side friction before treatment application
Table 36. SN65 Estimated available side friction first after treatment application
Table 37. SN65 estimated available side friction second after treatment application
Table 38. Descriptive statistics for passenger cars for margin of safety analysis
Table 39. Friction demand and supply comparison
Table 40. OSB treatment location site characteristics
Table 41. Northbound Pierce Ferry Road before data
Table 42. Southbound Shinarump Road before data
Table 43. Southbound Diamond Bar Road before data
Table 44. Southbound County Route 1 before data
Table 45. Alabama Location #1 before data
Table 46. Alabama Location #2 before data
Table 47. Alabama Location #3 before data
Table 48. Alabama Location #4 before data
Table 49. Alabama Location #5 before data
Table 50. Alabama Location #6 before data
Table 51. Alabama Location #7 before data
Table 52. Alabama Location #8 before data
Table 53. Southbound Tucker Road before data
Table 54. Northbound Tucker Road before data
Table 55. Southbound Reed Road before data
Table 56. Southbound New Boston Road before data
Table 57. Northbound New Boston Road before data
Table 58. Southbound Braley Hill Road before data
Table 59. Northbound Braley Hill Road before data
Table 60. Before-after operating speeds at northbound Pierce Ferry Road
Table 61. Before-after operating speeds at southbound Shinarump Road
Table 62. Before-after operating speeds at southbound Diamond Bar Road
Table 63. Before-after operating speeds at southbound County Route 1
Table 64. Before-after operating speeds at Alabama Location #1
Table 65. Before-after operating speeds at Alabama Location #2
Table 66. Before-after operating speeds at Alabama Location #3
Table 67. Before-after operating speeds at Alabama Location #4
Table 68. Before-after operating speeds at Alabama Location #5
Table 69. Before-after operating speeds at Alabama Location #6
Table 70. Before-after operating speeds at Alabama Location #7
Table 71. Before-after operating speeds at Alabama Location #8
Table 72. Before-after operating speeds at southbound Tucker Road
Table 73. Before-after operating speeds at northbound Tucker Road
Table 74. Before-after operating speeds at southbound Reed Road
Table 75. Before-after operating speeds at southbound New Boston Road
Table 76. Before-after operating speeds at northbound New Boston Road
Table 77. Before-after operating speeds at southbound Braley Hill Road
Table 78. Before-after operating speeds at northbound Braley Hill Road
Table 79. Change in speeds for Arizona sites
Table 80. Change in speeds for Alabama sites
Table 81. Change in speeds for Massachusetts sites
Table 82. Speed difference between the control point and the curve midpointle
Table 83. Speed difference between the approach and the PC
Table 84. Speed difference between the control point and the PC
Table 85. Speed difference between the control point and the curve midpoint
Table 86. Speed difference between the approach and the PC
Table 87. Speed difference control Point to PC
Table 88. Difference between the control point and the curve midpoint
Table 89. Difference between the approach and the PC
Table 90. Difference between the control point and the PC
Table 91. Number of vehicles exceeding the PSL in Arizona
Table 92. Number of vehicles exceeding the PSL in Alabama
Table 93. Number of vehicles exceeding the PSL in Massachusetts
Table 94. Change in standard deviation of speed in Arizona
Table 95. Change in standard deviation of speed in Alabama
Table 96. Change in standard deviation of speed in Massachusetts
Table 97. Number of segments by lane-width and shoulder-width
Table 98. Number of segments with roadside barriers
Table 99. Number of segments by driveway
Table 100. Alignment indices for quantifying horizontal alignment characteristics (based on Fitzpatrick et al., 2000)
Table 101. Number of segments with no-passing zone, one-sided passing zone, and shoulder rumble strip
Table 102. Descriptive statistics for geometric, traffic control, and traffic variables
Table 103. Descriptive statistics for crash variables
Table 104. Negative binomial regression model estimation results for total crashes (all types and severities).
Table 105. Negative binomial regression model estimation results for fatal-plus-injury crashes (All types).
Table 106. CMFs for Geometric Design Features
Table 107. Negative binomial regression model estimation results for property damage only crashes (all severities)
Table 108. Negative binomial regression model estimation results for single-vehicle crashes (all severities)
Table 109. Negative binomial regression model estimation results for multiple-vehicle crashes (all severities)
Table 110. Negative binomial regression model estimation results for key lane width/shoulder width crashes (all severities)
Table 111. Negative binomial regression model estimation results for single-vehicle crashes (fatal-plus-injury)
Table 112. Negative binomial regression model estimation results for multiple-vehicle crashes (fatal-plus-injury)
Table 113. Negative binomial regression model estimation results for key lane-width/shoulder- width crashes (fatal-plus-injury)
Table 114. Negative binomial regression model estimation results for single-vehicle crashes (PDO)
Table 115. Negative binomial regression model estimation results for multiple-vehicle crashes (PDO)
Table 116. Negative binomial regression model estimation results for key lane-width/ shoulder-width crashes (PDO)
Table 117. Multinomial logit model estimation results for total crashes (all types and severities)—base outcome: PDO
Table 118. Multinomial logit model estimation results for fatal-plus-injury crashes (all types)— base outcome: possible injury

LIST OF ABBREVIATIONS

AASHTO American Association of State Highway and Transportation Officials

ALDOT Alabama Department of Transportation

ANOVA Analysis of Variance

CMF Crash Modification Factors

CT Circular Texture

DF Dynamic Friction

FHWA Federal Highway Administration GIS Geographic Information System HCM Highway Capacity Manual

HDM Highway Data Management HFST High Friction Surface Treatment HSIS Highway Safety Information System HSM Highway Safety Manual

IFI International Friction Index KML Keyhole Markup Language MCPW Mohave County Public Works MM Mile Marker

MPD Mean Profile Depth

MPH Miles per Hour

MUTCD Manual on Uniform Traffic Control Devices NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NJDOT New Jersey Department of Transportation

OSB Optical Speed Bars P.E. Professional Engineer PC Point of Curvature

PDO Property Damage Only

PennDOT Pennsylvania Department of Transportation

PI Point of Intersection PSL Posted Speed Limit PT Point of Tangent

PTOE Professional Traffic Operations Engineer

RSA Road Safety Audit

SD Standard Deviation

SDF Severity Distribution Function

SN Skid Number

SRPEDD Southeast Regional Planning and Economic Development District

TRB Transportation Research Board

TWLTL Two-Way Left-Turn Lane

VBA Visual Basic for Applications

WVDOT West Virginia Department of Transportation

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