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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-17-098 Date: January 2018 |

Publication Number: FHWA-HRT-17-098 Date: January 2018 |

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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 the basis of miles driven per vehicle. A self-enforcing road (sometimes referred to as a “self-explaining roadway”) is a roadway that is planned and designed to encourage drivers to select operating speeds in harmony with the posted speed limit. Properly designed self-enforcing roadways can be effective in producing speed compliance and may contribute to less severe crash outcomes.

The purpose of this report is to provide guidance on how to produce self-enforcing roadways. The concepts can be applied to planned and existing roadways. This report should be useful to transportation professionals, State departments of transportation, and researchers interested in designing and/or retrofitting roadways to induce drivers to drive at more appropriate speeds.

Monique R. Evans, P.E.

Director, Office of Safety

Research and Development

**Notice**

This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

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.

1. Report No.FHWA-HRT-17-098 |
2. Government Accession No. |
3. Recipients Catalog No. |
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4. Title and SubtitleSelf-Enforcing Roadways: A Guidance Report |
5. Report DateJanuary 2018 |
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6. Performing Organization Code |
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7. Author(s)Eric Donnell, Kristin Kersavage, and Lisa Fontana Tierney |
8. Performing Organization Report No. |
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9. Performing Organization Name and AddressInstitute of Transportation Engineers 1627 Eye Street NW, Suite 600 Washington, DC 20006 Penn State University 212 Sackett Building University Park, PA 16802 |
10. Work Unit No. |
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11. Contract or Grant No.DTFH61-13-D-00026/0007 |
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12. Sponsoring Agency Name and AddressU.S. Department of Transportation Federal Highway Administration Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101 |
13. Type of Report and Period CoveredFinal Report; July 2015-November 2017 |
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14. Sponsoring Agency Code: |
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15. Supplementary NotesThe Task Order Manager for this report is Abdul Zineddin (HRDS-10). |
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16. AbstractThe objective of this project was to develop a guidance report to identify methods that may produce self-enforcing, or self-explaining, roadways during the geometric design process. While safety performance associated with these methods is not well understood yet, an implied outcome of effective speed management is that less severe crashes will result via the application of self-enforcing, or self-explaining, road design principles. Six self-enforcing road concepts and the processes needed to implement the concepts when designing or evaluating existing two-lane rural highways are identified and described in this document. It is anticipated that the concepts may be used to design roadways that produce operating speeds consistent with the desired operating speeds of the roadway. The six methods include: (1) the speed feedback loop process, (2) the inferred design speed approach, (3) design consistency methods, (4) applying geometric design criteria, (5) using a combination of signs and pavement markings, and (6) setting rational speed limits. |
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17. Key WordsSelf-enforcing road, self-explaining road, two-lane rural highway, operating speed, speed limit, design speed, speed management, safety |
18. Distribution StatementNo restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.http://www.ntis.gov |
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19. Security Classif. (of this report)Unclassified |
20. Security Classif. (of this page)Unclassified |
21. No. of Pages:118 |
22. Price |

**Form DOT F 1700.7 (8-72)** Reproduction of completed pages authorized.

**SI* (Modern Metric) Conversion Factors**

**EXECUTIVE SUMMARY****CHAPTER 1. INTRODUCTION****CHAPTER 2. RELATIONSHIP BETWEEN SPEED AND SAFETY****CHAPTER 3. RELATIONSHIP BETWEEN SPEED AND GEOMETRIC DESIGN****CHAPTER 4. SELF-ENFORCING ROAD CONCEPTS**- METHOD 1—SPEED FEEDBACK LOOP
- Step 1—Consider the Land Use, Topography, and Functional Class
- Step 2—Determine a Target or Anticipated Operating Speed
- Step 3—Determine the Design Speed of the Roadway
- Step 4—Acquire Roadway Geometric Information
- Step 5—Check for Consistency Between Design Elements and Anticipated Operating Speeds
- Step 6—Set Posted Speed Limit

- METHOD 2—INFERRED DESIGN SPEED APPROACH
- METHOD 3—DESIGN CONSISTENCY METHODS
- METHOD 4—APPLY EXISTING GEOMETRIC DESIGN CRITERIA
- METHOD 5—COMBINATION OF SIGNS AND PAVEMENT MARKINGS
- METHOD 6—SETTING RATIONAL SPEED LIMITS

- METHOD 1—SPEED FEEDBACK LOOP
**CHAPTER 5. CASE STUDY EXAMPLES****CHAPTER 6. CONCLUSIONS****APPENDIX A. OPERATING SPEED EQUATIONS****APPENDIX B. INFERRED DESIGN SPEED CALCULATIONS USING HORIZONTAL AND VERTICAL CURVATURE****GLOSSARY****REFERENCES**

- Figure 1. Equation. Relationship between kinetic energy, mass, and speed that occurs during a crash
- Figure 2. Equation. Expected number of injury crashes because of a change in the average operating speed
- Figure 3. Equation. Expected number of varying crash types as a result of a change in average operating speed
- Figure 4. Graph. Crash involvement rate as speed deviates from average travel speed from studies by Solomon (1964) and Cirillo (1968). (Stuster et al. 1998, figure 1)
- Figure 5. Equation. Radius of curvature. (AASHTO 2011)
- Figure 6. Equation. Braking distance for level vertical grade. (AASHTO 2011)
- Figure 7. Equation. Braking distance when vertical grade exists. (AASHTO 2011)
- Figure 8. Equation. SSD. (AASHTO 2011)
- Figure 9. Equation. HSO. (AASHTO 2011)
- Figure 10. Equation. Typical linear model
- Figure 11. Equation. Model for speed on tangent roadway sections
- Figure 12. Equation. Model for speed on horizontal curve roadway sections. (Figueroa Medina and Tarko 2005)
- Figure 13. Graph. Radius of curvature versus 85th-percentile speeds and design speeds
- Figure 14. Graph. Degree of curvature versus 85th-percentile speeds
- Figure 15. Equation. Geometric measure of tangent section and attached curves for long tangent length
- Figure 16. Equation. Geometric measure for short tangent lengths
- Figure 17. Graph. Geometric measure for long tangent lengths and attached curves versus 85th-percentile speeds
- Figure 18. Graph. Geometric measure of short tangent section versus 85th-percentile speeds
- Figure 19. Equation. Model for the speed-tangent relationship. (Polus et al. 2000)
- Figure 20. Graph. Tangent lengths versus 85th-percentile speeds for
*e*= 12 percent - Figure 21. Equation. Crest vertical curve length when sight distance is less than the vertical curve length
- Figure 22. Equation. Crest vertical curve length when sight distance is greater than the vertical curve length
- Figure 23. Equation. Length of sag vertical curve when headlamp beam distance is less than the length. (AASHTO 2011)
- Figure 24. Equation. Length of sag vertical curve when headlamp beam distance is less than the length-reduced equation. (AASHTO 2011)
- Figure 25. Equation. Length of sag vertical curve when headlamp beam distance is greater than the length. (AASHTO 2011)
- Figure 26. Equation. Length of sag vertical curve when headlamp beam distance is greater than the length reduced equation. (AASHTO 2011)
- Figure 27. Graph. Rate of vertical curvature versus 85th-percentile speeds and design speeds
- Figure 28. Flowchart. Operating speed approach for design of two-lane, two-way roadways. (TAC 1999, figure 1.2.3.1)
- Figure 29. Flowchart. Proposed framework to improve design speed concept. (Adapted from Donnell et al. 2002, figure 4)
- Figure 30. Illustration. US Route 6 speed profile. (Donnell et al. 2009b)
- Figure 31. Flowchart. Framework for inferred design speed approach
- Figure 32. Equation. Horizontal curve
- Figure 33. Equation. Algebraic difference in grades. (AASHTO 2011)
- Figure 34. Equation. Length of crest vertical curve when SSD is less than the length. (AASHTO 2011)
- Figure 35. Equation. Length of crest vertical curve when SSD is greater than the length. (AASHTO 2011)
- Figure 36. Equation. Length of sag vertical curve when SSD is greater than the length. (AASHTO 2011)
- Figure 37. Equation. Length of sag vertical curve when SSD is less than the length. (AASHTO 2011)
- Figure 38. Equation. Available SSD. (AASHTO 2011)
- Figure 39. Flowchart. Framework for using design consistency methods
- Figure 40. Graph. Ranges of radius of curvature for 85th-percentile and design speeds
- Figure 41. Flowchart. Framework for applying geometric design criteria
- Figure 42. Photo. Centerline and edge line pavement markings on road
- Figure 43. Photo. Advisory speed limit sign
- Figure 44. Photo. Chevron signs around a horizontal curve
- Figure 45. Photo. Chevron pavement markings on a road
- Figure 46. Photo. Red speed limit pavement marking on road
- Figure 47. Photo. Optical speed bars on a road
- Figure 48. Photo. Speed limit sign with red border
- Figure 49. Photo. SLOW pavement marking in middle of lane on a road before a horizontal curve
- Figure 50. Photo. Dynamic speed feedback sign on the side of a road
- Figure 51. Photo. White speed limit pavement marking in middle of lane
- Figure 52. Photo. Speed-activated speed-limit-reminder sign
- Figure 53. Photo. YOU ARE SPEEDING IF FLASHING sign on side of road
- Figure 54. Photo. Transverse pavement markings painted on travel lanes
- Figure 55. Photo. Transverse pavement markings painted on travel lane
- Figure 56. Photo. Dynamic variable message sign displaying speed limit and traffic information
- Figure 57. Photo. Zigzag pavement markings painted on a lane
- Figure 58. Flowchart. Framework for setting rational speed limits
- Figure 59. Map. US Route 6 study segment map
- Figure 60. Illustration. US Route 6 plan view
- Figure 61. Illustration. US Route 6 typical cross section
- Figure 62. Graph. US Route 6 speed profile
- Figure 63. Illustration. US Route 6 IHSDM output
- Figure 64. Map. SR 865 (Rockfish Road) study segment map
- Figure 65. Illustration. SR 865 (Rockfish Road) plan view
- Figure 66. Illustration. SR 865 (Rockfish Road) typical cross section
- Figure 67. Graph. SR 865 (Rockfish Road) speed profile
- Figure 68. Illustration. SR 865 (Rockfish Road) IHSDM output
- Figure 69. Equation. Available SSD
- Figure 70. Equation. Using available SSD equation to solve for inferred design speed
- Figure 71. Equation. Algebraic difference in grades
- Figure 72. Equation. Inputting given information to solve for algebraic difference in grades
- Figure 73. Equation. Length of vertical curve
- Figure 74. Equation. Inputting given information to solve for length of vertical curve
- Figure 75. Equation. Point-mass model to determine inferred design speed. (AASHTO 2011)
- Figure 76. Equation. Point-mass model to solve for the side-friction demand factor
- Figure 77. Equation. Inputting given information into the point-mass model
- Figure 78. Equation. Reducing inputted information in the point-mass model
- Figure 79. Equation. Calculating the side-friction demand factor for a design speed of 50 mph (80.5 km/h)
- Figure 80. Equation. Calculating the side-friction demand factor for a design speed of 55 mph (88.5 km/h)
- Figure 81. Equation. Calculating the side-friction demand factor for a design speed of 53 mph (85.3 km/h)
- Figure 82. Equation. Calculating the side-friction demand factor for a design speed of 52 mph (83.7 km/h)
- Figure 83. Equation. HSO. (AASHTO 2011)
- Figure 84. Equation. Using HSO equation to solve for radius of curve
- Figure 85. Equation. Point-mass model to determine inferred design speed
- Figure 86. Equation. Inputting given information into the point-mass model (step 1)
- Figure 87. Equation. Inputting given information into the point-mass model (step 2)
- Figure 88. Equation. Calculating the side-friction demand factor for a design speed of 70 mph (112.7 km/h). (AASHTO 2011)
- Figure 89. Equation. Calculating the side-friction demand factor for a design speed of 67 mph (107.8 km/h). (AASHTO 2011)
- Figure 90. Equation. Calculating the side-friction demand factor for a design speed of 66 mph (106.2 km/h). (AASHTO 2011)

- Table 1. Power function exponents for various crash severities for rural roads/freeways. (Elvik 2009, table 18)
- Table 2. Effects of speed increases on severity of crashes. (Kockelman et al. 2006)
- Table 3. The increase in probability of a fatality and injury due to an increase in speed limit determined from accident-severity models. (Malyshkina and Mannering 2008, table 2)
- Table 4. Safety effects of speed increases. (Kockelman et al. 2006)
- Table 5. Interpretation of the mean speed and speed deviation model produced by Himes et al. (2011)
- Table 6. Interpretation of the mean speed equations for curve and tangent segments (figure 11 and figure 12) produced by Figueroa Medina and Tarko (2005)
- Table 7. Example using the tangent segments mean speed model from Figueroa Medina and Tarko (2005)
- Table 8. Example using the horizontal curves mean speed model from Figueroa Medina and Tarko (2005)
- Table 9. Example using the mean speed model from Himes et al. (2011)
- Table 10. Example using the tangent segments speed dispersion/deviation model from Figueroa Medina and Tarko (2005)
- Table 11. Example using the horizontal curves speed dispersion/deviation model from Figueroa Medina and Tarko (2005)
- Table 12. Example using the speed dispersion/deviation model from Himes et al. (2011)
- Table 13. Minimum width of traveled way for rural arterials (AASHTO 2011, table 7-3)
- Table 14. Minimum width of usable shoulder for rural arterials (AASHTO 2011, table 7-3)
- Table 15. Equations used to calculate vehicle operating speeds
- Table 16. Sign and pavement marking roadway treatments that possible affect speeds. (Boodlal et al. 2015)
- Table 17. US Route 6 58th-percentile speed profile coordinates
- Table 18. US Route 6 design speed assumption
- Table 19. US Route 6 speed differential of adjacent design element
- Table 20. US Route 6 USLIMITS2 basic project factor inputs
- Table 21. US Route 6 USLIMITS2 roadway factor inputs
- Table 22. US Route 6 USLIMITS2 traffic factor inputs
- Table 23. Historical crash data for the US Route 6 study segment
- Table 24. Comparison of historical crash data and number of crashes predicted using the IHSDM
- Table 25. SR 865 (Rockfish Road) 85th-percentile speed profile coordinates
- Table 26. SR 865 (Rockfish Road) design speed assumption
- Table 27. SR 865 (Rockfish Road) speed differential of adjacent design element
- Table 28. SR 865 (Rockfish Road) USLIMITS2 basic project factor inputs
- Table 29. SR 865 (Rockfish Road) USLIMITS2 roadway factor inputs
- Table 30. SR 865 (Rockfish Road) USLIMITS2 roadway factor inputs
- Table 31. Historical crash data for the SR 865 (Rockfish Road) study segment
- Table 32. Comparison of reported to predicted crashes on SR 865
- Table 33. Equations from literature used to determine operating speeds

AADT | annual average daily traffic (vehicles per day) |
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AASHTO | American Association of State Highway and Transportation Officials |

DCM | Design Consistency Module |

EB | empirical Bayes |

FHWA | Federal Highway Administration |

HSM | Highway Safety Manual |

HSO | horizontal sight line offset |

IHSDM | Interactive Highway Safety Design Model |

ITE | Institute of Transportation Engineers |

MUTCD | Manual on Uniform Traffic Control Devices |

NHTSA | National Highway Traffic Safety Administration |

OLS | ordinary least squares |

SHRP2 | Second Strategic Highway Research Program |

SSD | stopping sight distance |

TAC | Transportation Association of Canada |

TRB | Transportation Research Board |