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Federal Highway Administration Research and Technology
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This report is an archived publication and may contain dated technical, contact, and link information |
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Publication Number: FHWA-HRT-10-038
Date: October 2010 |
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Balancing Safety and Capacity in an Adaptive Signal Control System — Phase 1PDF Version (1.40 MB)
PDF files can be viewed with the Acrobat® Reader® ForewordVirtually all previous research addressing intersection safety and capacity has dealt with the two issues independently. Over the past 20 years, advancements in real-time adaptive signal timing strategies for intersections and arterials have improved signal operations by improving traffic flow efficiency, but most optimization algorithms do not include performance measures for safety. At this time, little is known about the relationships between signal timing parameters (e.g., cycle time, offsets, phase sequence, etc.) and safety that can be of benefit to traffic engineering practitioners. This research, comprising two phases, focuses on the development of real-time signal timing methodologies and algorithms that balance safety and efficiency. This report summarizes phase 1, which examines relationships between signal timing parameters and surrogate measures of safety such as rear-end, angle, and lane-change conflicts. These single variable relationship studies determine the parameters that are most likely to offer benefits in an adaptive, real-time strategy. Phase 1 also identifies an experimental design methodology to compute the effect of a change to signal timing parameters and develops both procedures for calculating performance and algorithms for improving the traffic system based on safety and existing principles of adaptive control used in the Federal Highway Administration (FHWA) Adaptive Control Systems (ACS) Lite system. The ultimate objective of this research is to develop algorithms that can balance the performance of the traffic control system for both efficiency and safety and that can work with state-of-the-practice signal controllers. 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. 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
SI* (Modern Metric) Conversion Factors TABLE OF CONTENTS
3.0 ANALYSIS AND SIMULATION METHODOLOGIES 4.0 STUDY SCENARIOS AND SURROGATE MEASURES OF SAFETY 5.0 FINDINGS FROM THE SIMULATION ANALYSIS
6.0 PHASE 2 RESEARCH AND DEVELOPMENT
LIST OF FIGURES Figure 1. Screenshot. SSAM's color-coded conflicts Figure 2. Chart. Operational concept of SSAM Figure 3. Illustration. SSAM's zone grid Figure 4. Illustration. Vehicle path Figure 5. Illustration. DIS1 and DIS2 Figure 6. Illustration. Checking a conflict between two vehicles at MaxTTC Figure 8. Illustration. Conflict types by angle Figure 9. Illustration. Lane-change conflict Figure 10. Illustration. Conflict angle Figure 11. Illustration. Clock angle Figure 12. Illustration. Intersection configuration used in simulation tests Figure 13. Illustration. Arterial configuration used in simulation tests Figure 14. Illustration. Typical intersection layout Figure 15. Illustration. Intersection traffic volumes Figure 16. Illustration. Three-intersection arterial Figure 17. Illustration. Detail of intersection in three-intersection arterial Figure 18. Illustration. Demand volumes for 50-s cycle (vehicles per hour) Figure 19. Illustration. Demand volumes for 105-s cycle (vehicles per hour) Figure 20. Screenshot. Synchro™s representation of flows impacted by offset changes Figure 21. Screenshot. Typical summary of statistical distribution data Figure 22. Screenshot. An excerpt of t-test statistical output from SSAM Figure 24. Chart. Flow chart of cycle time tuning algorithm Figure 25. Illustration. Typical flow profile detector locations on coordinated approaches Figure 26. Illustration. Example of volume and occupancy data from a typical advance detector Figure 27. Illustration. Example of phase timing for each of the last several cycles Figure 29. Chart. Offset adjustment algorithm flow chart Figure 30. Diagram. Ring diagram with barriers denoted by bold vertical lines Figure 31. Screenshot. A complete utilization-detector layout for ACS Lite Figure 32. Illustration. Measuring phase utilization for coordinated-actuated controllers Figure 33. Graph. Utilization of phases before split adjustment Figure 34. Graph. Utilization of phases after split adjustment Figure 35. Chart. Flow chart of the split optimization process including safety analysis Figure 36. Chart. Flow chart of algorithms execution sequence LIST OF TABLES Table 1. Potential relationships between signal timing parameters and conflict types Table 2. Measures of conflict severity Table 3. Single intersection base condition Table 4. Effects of changes in traffic demand under a fixed cycle length Table 5. Effects of changes in splits Table 6. Effects of changes in cycle length Table 7. Effects of changes in the main street detector extension setting Table 8. Effect of changes in the side street detector extension setting Table 9. Effects of changes in left-turn phasing from protected only to protected/permissive Table 10. Effects of changes in left-turn phasing from protected to permissive left-turn only Table 11. Effects of changes in the phase-change interval Table 12. Arterial base condition with arterial traffic demand of V/C = 0.85 Table 13. Arterial base condition with changes in arterial traffic demand to V/C = 1.0 Table 14. Effects of changes in offsets with cycle length of 50 s Table 15. Effects of changes in offsets with cycle length of 105 s Table 16. Effects of changes in left-turn phase sequence to lead-lag, 50-s cycle length Table 17. Effects of changes in left-turn phase sequence to lead-lag, 105-s cycle length Table 18. Summary of conflict data for the intersection baseline analysis Table 19. Average conflicts under different demand conditions Table 20. Ratio of conflicts to V/C Table 21. Conflicts under different split conditions Table 22. Ratio of conflicts to changes per hour (various split conditions) Table 23. Conflicts with main street split adjustments Table 24. Conflicts with side street split adjustments Table 25. Conflicts under different cycle lengths Table 26. Ratio of conflicts to changes per hour (various demand conditions) Table 27. Conflicts under different main street detector extension times Table 28. Conflicts under different side street extension times Table 29. Total conflicts with protected/permissive phasing versus protected-only phasing Table 30. Conflict by type for protected only and protected-permissive Table 31. Conflicts with permissive left-turn phasing (unprotected left turn) Table 32. Total conflicts with protected/permissive phasing versus protected-only phasing Table 33. Total conflicts with different Y+AR times Table 34. Arterial conflicts by type Table 35. Conflicts under different offset conditions (50-s cycle length) Table 36. Conflicts under different offset conditions (105-s cycle length) Table 37. Arterial conflicts with lead-lag left-turn phasing (50-s cycle, V/C = 0.85) Table 38. Arterial conflicts with lead-lag left-turn phasing (105-s cycle, V/C=1.0) Table 39. Parameter-conflict association Table 40. Fractional factorial design approach using linear regression models Table 41. CCD approach using nonlinear regression models Table 42. Example utilization of phases before and after split adjustment Table 43. Rules to evaluate to consider changing phase sequence Table 44. Rules to evaluate when considering changing left-turn treatment LIST OF ACRONYMS AND ABBREVIATIONS
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