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Interactive Highway Safety Design Model (IHSDM)

Interactive Highway Safety Design Model (IHSDM). By Josh Hinds. Outline. Background of IHSDM Description of the Modules New Features An IHSDM Project from Start to Finish Future Developments Conclusion. What is IHSDM?.

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Interactive Highway Safety Design Model (IHSDM)

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  1. Interactive Highway Safety Design Model (IHSDM) By Josh Hinds

  2. Outline • Background of IHSDM • Description of the Modules • New Features • An IHSDM Project from Start to Finish • Future Developments • Conclusion The Modules

  3. What is IHSDM? IHSDM is a suite of software analysis tools that evaluate the safety and operational effects of the geometric design on two-lane rural highways. (www.ihsdm.org) Background

  4. What is IHSDM? • Safety analysis tool, not specifically used for designing. • Evaluates the geometric design of the highway. • Two-lane rural highways • Compares user inputted design to designated design standards. Background

  5. Why Was IHSDM Needed? • 77% of the Nation’s highways are two-lane rural highways • 41% of all the fatal crashes occur on two-lane rural highways • Citizens demand increased safety on two-lane rural highways The Modules

  6. Why Was IHSDM Needed? • The highway network is getting older. • Stakeholders are expecting safer highways on the same budget. • Highway designs need to be checked for safety ‘black spots’. Background

  7. How Does IHSDM Help? • Makes use of five software modules that analyze the geometric design of the highway • Policy Review • Crash Prediction • Design Consistency • Traffic Analysis • Intersection Review Background

  8. Framework of the IHSDM Program IHSDM is composed of these modules. Background

  9. How Does IHSDM Work? • The user inputs the design file. • The five modules compare the inputted design values to the AASHTO policy standard values. • IHSDM determines how far out of range the values are and provides feedback to the user. Background

  10. How Can IHSDM Benefit the Designer? • Intended to be used throughout the design process. • Can be used on new construction and existing facilities. • Provides a Quality Assurance check throughout the design process. Background

  11. How Can IHSDM Benefit the Designer? • Find ‘Accident Black Spots’ before construction. • Save money by lowering crash rates and eliminating the reconstruction of unsafe areas. • Double check design values. • Uses design software format. Background

  12. How Can IHSDM Benefit the Designer? • Helps project developers improve the expected safety performance of the final design. • Justifies and defends geometric design decisions. Background

  13. How Can IHSDM Benefit the Designer? • AASHTO A Policy on Geometric Design of Highways and Streets "Green Book" • AASHTO Roadside Design Guide • AASHTO Guide for Development of Bicycle Facilities • Numerous Editions and Metric/English Background

  14. How Can IHSDM Benefit the Designer? • Public perception that the roadway is ‘safe’. • Estimates the expected crash frequency for the geometric design. • Analyzes other safety and operation performance measurements. (SSD, superelevation, etc.) (Turner-Fairbank) Background

  15. What is ‘Safe’? • Every roadway will have crashes. • ‘Safe’ (past) • Meeting a minimum set of design criteria. • ‘Safe’ (presently) • Comparison of number of crashes to sites with similar characteristics. (FHWA, Paniati) Background

  16. The Modules • FHWA was in charge of all the research • FHWA received input from numerous state agencies, consulting firms, and academic institutions. • Based on research received from field data. The Modules

  17. Policy Review Module • Automates the process of checking geometric design elements against relevant design policy standards. • Construction or Reconstruction • Quality Assurance / Quality Control The Modules

  18. Policy Review Module • Cross Section (traveled-way, auxillary, shoulder) • Horizontal and Vertical Alignment • Sight Distance • Items with an asterisk will be compared to FHWA standards. The Modules

  19. Policy Review Module • Summary of what will be analyzed The Modules

  20. Policy Review Module Results The Modules

  21. Crash Prediction Module • Identifies improvement projects on existing highways • Estimates the frequency and severity of crashes. • Compares the safety performance of design alternatives • Will assess that safety cost effectiveness of design decisions. The Modules

  22. Crash Prediction Module • Uses the Empirical Bayes Method • Algorithm for estimating crashes combines base models and accident modification factors • Highway segments and intersections • 3-leg stop control on the minor • 4-leg with stop control on the minor • 4-leg signalized The Modules

  23. The Modules

  24. Crash Prediction Module - The crash history The Modules

  25. Crash Prediction Module • Table • Crash Rate • By Design Element • By Segment • Crash Type • Graph • Expected Frequency • Crash Rate • By Design Element • By Segment The Modules

  26. Crash Prediction Modulus • Module provides a comment section to inform the user of any areas not addressed. • Summary of what will be analyzed, and how the results are formatted. • Module runs analysis. The Modules

  27. Crash Prediction Modulus Results The Modules

  28. Design Consistency Module • Provides a Quality Assurance check on the consistency of the design. • Allows designer to double-check design assumptions. • Some designs conform to policies, but can not be consistent for the drivers. • Heavily focused on Horizontal Curves. The Modules

  29. Design Consistency Module • Drivers are more likely to make mistakes at features that violate their human inclination. • Reduction of speed in tangent before horizontal curve. • Design speed vs. 85th percentile speed. • Design conformance vs. driver’s expectations The Modules

  30. Design Consistency • Desired Speed = 85th percentile speed • 62 mph was determined by studies in six states. • Tangent Speed The Modules

  31. Design Speed Assumption Check Conditions KeyCondition 1: 0 mph <= (V85 - Vdesign) <= 6 mphCondition 2: 6 mph < (V85 - Vdesign) <= 12 mphCondition 3: 12 mph < (V85 - Vdesign)Condition 4: (V85 - Vdesign) < 0 mphwhere:V85 = estimated 85th percentile operating speed (mph)Vdesign = design speed (mph)

  32. Traffic Analysis Module • Evaluates the operational effects of the current and future traffic estimates. • Can be used to determine the effects of alternatives. (realignment, cross-section improvements, and additional passing lanes) • Construction or Reconstruction The Modules

  33. Traffic Analysis Module • Uses the TWOPAS rural traffic simulation model for two-lane highways. • QC/QA • Provides documentation for design exceptions • Determines the time following other vehicles The Modules

  34. Traffic Analysis Module • Traffic Flow • Traffic characteristics • Highway Elements • Time Parameters • Results The Modules

  35. Traffic Analysis Module • TWOPAS • Traffic Simulation Model • User can specify traffic demand and vehicle mix. • Also, can specify horizontal and vertical alignment. • Models 13 types of vehicles with performance characteristics for each. The Modules

  36. Intersection Review Module • Not currently used in the 2006 edition. • Research and module are complete. • Still in the final testing phase. • Expect the Intersection Review module to be released very soon as an update to the 2006 edition. The Modules

  37. Intersection Review Module • Diagnostic review of the expected performance. • Uses the ‘Expert System’ • Stopping Sight Distance • Corner radius and turn lane design. The Modules

  38. The future of IHSDM • IHSDM is constantly being updated for the newest standards. • Research and data collection continues for all modules. • Additional modules are being researched and created. (intersection review) • Multi-Lane highways The Modules

  39. Conclusion Questions? The Modules

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