Speed Prediction for Two-Lane Rural Highways PUBLICATION NO. 99-171 AUGUST 2000 Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. FHWA-RD-99-171 4. Title and Subtitle 5. Report Date SPEED PREDICTION FOR TWO-LANE RURAL HIGHWAYS 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Kay Fitzpatrick, Lily Elefteriadou, Douglas W. Harwood, Jon M. Collins, John McFadden, Ingrid B. Anderson, Raymond A. Krammes, Nelson Irizarry, Kelly D. Parma, Karin M. Bauer, and Karl Passetti 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Texas Transportation Institute The Texas A&M University System 11. Contract or Grant No. College Station, Texas 77843-3135 DTFH61-95-R-00084 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Office of Safety Research and Development Final Report Federal Highway Administration September 1995 - June 1999 6300 Georgetown Pike 14. Sponsoring Agency Code McLean, Virginia 22101-2296 15. Supplementary Notes Contracting Officer’s Technical Representative (COTR): Ann Do, HRDS; [email protected] 16. Abstract Design consistency refers to the conformance of a highway’s geometry to driver expectancy. Drivers make fewer errors in the vicinity of geometric features that conform to their expectations. A technique to evaluate the consistency of a design is to evaluate changes in operating speeds along an alignment. To use operating speed as a consistency tool requires the ability to accurately predict speeds as a function of the roadway geometry. In this research project, several efforts were undertaken to predict operating speed for different conditions such as on horizontal, vertical, and combined curves; on tangent sections using alignment indices; on grades using the TWOPAS model; and prior to or after a horizontal curve. The findings from the different efforts were incorporated into a speed-profile model. The model can be used to evaluate the design consistency of the roadway or can be used to develop a speed profile for an alignment. The model considers both horizontal and vertical curvature and the acceleration or deceleration behavior as a vehicle moves from one feature to another. 17. Key Words 18. Distribution Statement Two-lane rural highway, speed-prediction equations, This document is available to the public via internet access acceleration/deceleration, IHSDM. at www.tfhrc.gov/safety/ihsdm/ihsdm.htm 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 217 Form DOT F 1700.7 (8-72) TABLE OF CONTENTS 1. INTRODUCTION .......................................................... BACKGROUND ......................................................... OBJECTIVES ............................................................ ORGANIZATION OF THE REPORT ......................................... 2. PREVIOUS WORK ON PREDICTING SPEEDS ON TWO-LANE RURAL HIGHWAYS ........................................................ EVALUATION OF DESIGN CONSISTENCY .................................. ESTIMATION OF OPERATING SPEED ...................................... SUMMARY OF LITERATURE REVIEW ...................................... 3. PREDICTING SPEEDS ON TWO-LANE RURAL HIGHWAY CURVES ............ DATA COLLECTION METHODOLOGY ..................................... SPEED-PREDICTION EQUATIONS FOR PASSENGER CARS ON HORIZONTAL AND VERTICAL CURVES ................................. PRELIMINARY MODEL DEVELOPMENT .................................... EVALUATION OF SPIRAL TRANSITIONS ................................... OTHER VEHICLE TYPES .................................................. SUMMARY ............................................................. 4. PREDICTING SPEEDS ON TANGENTS USING ALIGNMENT INDICES ........... PREVIOUS USES OF ALIGNMENT INDICES ................................. DEVELOPMENT OF ALIGNMENT INDICES ................................. ANALYSIS METHODOLOGY .............................................. RESULTS ............................................................... SUMMARY FOR ALIGNMENT INDICES .................................... 5. VEHICLE PERFORMANCE USING TWOPAS EQUATIONS ....................... TWOPAS MODEL ........................................................ VEHICLE-PERFORMANCE EQUATIONS FOR PASSENGER CARS AND RECREATIONAL VEHICLES ............................................ VEHICLE-PERFORMANCE EQUATIONS FOR TRUCKS ....................... SUMMARY FOR GRADE EFFECTS ......................................... 6. ACCELERATION/DECELERATION MODELING .............................. ACCELERATION/DECELERATION DATA COLLECTION ...................... DATA REDUCTION ...................................................... ACCELERATION/DECELERATION ASSUMPTIONS—VALIDATION TESTS ....... DEVELOPMENT OF ACCELERATION/DECELERATION MODELS ............... TABLE OF CONTENTS (continued) 7. VALIDATION OF SPEED-PREDICTION EQUATIONS ........................... VALIDATION OF SPEED-PREDICTION EQUATIONS FOR HORIZONTAL AND VERTICAL CURVES .............................................. VALIDATION OF PREDICTED-SPEED CHANGES ............................. SUMMARY-VALIDATION OF SPEED-PREDICTION EQUATIONS AND ACCELERATION/DECELERATION MODELS ......................... 8. DESIGN-CONSISTENCY EVALUATIONS AND SPEED-PROFILE MODEL ......... SPEED-PREDICTION EQUATIONS USING ALL AVAILABLE DATA ............. DESIGN-CONSISTENCY EVALUATION AND SPEED-PROFILE MODEL PROCEDURE ......................................................... SPEED-PROFILE EXAMPLE ............................................... DESIGN-CONSISTENCY EXAMPLE ........................................ SPEED-PROFILE MODEL ASSUMPTIONS ................................... 9. RELATIONSHIPS OF GEOMETRIC DESIGN-CONSISTENCY MEASURES TO SAFETY ................................................................... ANALYSIS METHODOLOGY/DATABASE DEVELOPMENT .................... ANALYSIS OF SPEED REDUCTION AS A DESIGN-CONSISTENCY CRITERION FOR HORIZONTAL CURVES ........................................... ANALYSIS OF ROADWAY ALIGNMENT INDICES AS DESIGN- CONSISTENCY CRITERIA ............................................. ANALYSIS OF RATIOS BETWEEN INDIVIDUAL DESIGN ELEMENTS AND ALIGNMENT INDICES .................................... CONCLUSIONS ......................................................... 10. SUMMARY, FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS .......... SUMMARY ............................................................. FINDINGS .............................................................. CONCLUSIONS ......................................................... RECOMMENDATIONS ................................................... REFERENCES ................................................................ LIST OF FIGURES Figure 1. Location of Piezoelectric Sensors on Horizontal Curves ............................. 2. Location of Radar Meters on Horizontal Curves ................................... 3. Location of Piezoelectric Sensors on Vertical Crest Curves With Limited Sight Distance ...................................................... 4. Horizontal Curves on Grades: V85 Versus R ...................................... 5. Horizontal Curves on Grades: V85 Versus 1/R ..................................... 1/2 6. Horizontal Curves on Grades: V85 Versus R .................................... 7. Vertical Crest Curves on Horizontal Tangents: V85 Versus 1/K ........................ 8. Vertical Sag Curves on Horizontal Tangents: V85 Versus 1/K ......................... 9. Estimated V85 Versus Radius: Horizontal Curves on Grades .......................... 10. Estimated V85 Versus Radius: Horizontal Curves on 0- to 4-Percent Grades ................. 11. Estimated V85 Versus K: Vertical Crest Curves (LSD) ................................. 12. Estimated V85 Versus K: Vertical Sag Curves ........................................ 13. Estimated V85 Versus R: Horizontal Curves With Different Vertical Alignment Conditions ....................................................... 14. V85 Horizontal Curve Versus Curve Length .......................................... 15. Cumulative Plot for Radius = 146 m ............................................... 16. Cumulative Plot for Radius = 291 m ............................................... 17. Cumulative Plot for Radius = 349 m ............................................... 18. Cumulative Plot for Radius = 437 m ............................................... 19. Truck and Recreational Vehicle Data Versus Radius (Passenger Vehicle Model, Grade: 0 Percent to 4 Percent) ........................... 20. Truck and Recreational Vehicle Data Versus Radius (Passenger Vehicle Model, Grade: 4 Percent to 9 Percent) ........................... 21. Truck and Recreational Vehicle Data Versus Radius (Passenger Vehicle Model, Grade: -9 Percent to 0 Percent) .......................... 22. Observed 85th Percentile Tangent Speeds Versus Preceding Horizontal Tangent Length ........ 23. Average Change in Alignment Indices by Distance .................................... 24. 85th Percentile Tangent Speed Versus CCR ......................................... 25. 85th Percentile Tangent Speed Versus Degree of Curvature .............................. 26. 85th Percentile Tangent Speed Versus Ratio of Curve Length to Road Length ................ 27. 85th Percentile Tangent Speed Versus