Adaptation of HERS-ST Models for the South Carolina Interactive Interstate Management System presented to the Transportation Research Board HERS Modeling and Data Integration Conference presented by William Robert Cambridge Systematics, Inc. April 2008 Transportation leadership you can trust.
Outline Interactive Interstate Management System (IIMS) Overview Modeling Approach Highway Segments Interchanges System Implementation Next Steps Questions 1
IIMS Overview Motivation for the System IIMS was conceived by and developed for South Carolina Department of Transportation (SCDOT) Goals Ranking of needs Testing project alternatives at a planning level Storing inventory and inspection data Initial focus was on interstate interchanges Initially developed as the Interactive Interchange Management System 2 Interstate highway segments added in Version 2.0
IIMS Overview Challenges Interstate interchanges and segments encompass a number of assets- roads, ramps, bridges, traffic control devices, right-of-way Data are dispersed Roadway inventory RIMS Bridge data Pontis (element data), RIMS (NBI) Ramp counts spreadsheet files Crash data traffic records Some needed data were not available 3 No prior established approach for ranking interchanges and highway sections
IIMS Overview System Scope IIMS Input Agency Policies Performance Targets Design Standards Inventory and Condition Data Roadway Inventory Bridge Inventory Traffic Data Accident Data Geometric Data Location Data Observed Deficiencies Capacity Safety Geometric IIMS Models Interchanges Evaluation Assess Current Conditions Generate Improvement Alternatives Predict Future Performance Highway Segments Evaluation Assess Current Conditions Generate Improvement Alternatives Predict Future Performance Ranking Define Ranking Schemes Calculate Performance Measures Generate Rankings Ranking Define Ranking Schemes Calculate Performance Measures Generate Rankings IIMS Results Ranked Lists Reports Diagrams Geospatial Views 4
IIMS Overview Development Timeline Version 1.0 released and piloted, data collection began for all SC interstate interchanges Work began on system design and development System conceived by SCDOT Version 1.1 released with complete interchange data set Version 2.1 released with support for highway segments Work proceeding on Version 2.1, 3.0 2003 2004 2005 2006 2007 2008 5
Modeling Approach Highway Segments Use of HERS Models Free flow speed (FFS) Function of lane width, lateral clearance, number of lanes, and interchange density Capacity Function of FFS, lanes, truck percent, type of terrain urban/rural designation, grade, curvature, speed limit, Present Serviceability Rating (PSR), directional factor and HPMS K factor Average effective speed Function of FFS, traffic, capacity, lanes, and number of shoulders 6
Modeling Approach Highway Segments Use of HERS Models (continued) Crashes per vehicle mile traveled (VMT) Function of traffic, capacity lane width, urban/rural designation Vehicle operating costs Calculated as detailed in Section E of the HERS-ST Technical Manual 7
Modeling Approach Highway Segments Measures Predicted Auto travel time costs, in hours and dollars Truck travel time costs, in hours and dollars Vehicle operating costs in dollars Crashes, in number of crashes and dollars All measures presented in terms of Totals Totals per VMT Totals per lane-mile 8
Modeling Approach Highway Segments Alternative Testing System predicts measures over a 20-year period based on existing conditions and/or a specified improvement 9 One can define an improvement alternative to change Number of lanes Peak hour lanes Lane width Speed limit Shoulder, median type and width Curvature Grade Traffic characteristics
Modeling Approach Highway Segments HPMS Sample Section Data Sample section data required for the HERS models Available of approximately 1/3 of the sections Determined that functional characteristics of SC interstates are very consistent, thus feasible to predict sample section data for universal sections from nearby sample sections Approach not feasible for non-interstate sections 10
Modeling Approach - Interchanges Use of Existing Modeling Approaches HERS Used to predict Average Effective Speed (AES) of a roadway to calculate travel time for movements through an interchange (simplified version of segment model) HCM 2000 Used for predicting delay for merging, unsignalized and signalized intersections 11 AASHTO Pontis User benefits for widening, raising, strengthening or replacing a structure Considers accident costs, commercial vehicle detour costs
Modeling Approach - Interchanges Measures Predicted Travel time Passenger vehicles Trucks Intersection delay Passenger vehicles Trucks Distance traveled Passenger vehicles Trucks 12
Modeling Approach - Interchanges Measures Predicted (continued) Commercial vehicle detour time Commercial vehicle detour distance Design-related crashes Fatal Personal injury Property damage only 13 Other crashes Fatal Personal injury Property damage only
Modeling Approach - Interchanges Crash Models Crashes at each interchange are designated as design related or non-design related these have been tabulated for each interchange A per-crash cost is specified for fatal crashes, crashes with non-fatal injuries, and crashes with property damage only Non-design related crashes are based on historic crash counts and are not affected by interchange improvements 14 If it is determined that an alternative addresses design related crashes, the predicted number of crashes is reduced to the statewide average
Modeling Approach - Interchanges Alternative Testing One can define an improvement alternative to change Ramp configuration Intersection configuration Address clearance, load issues on bridges Functional classification for crossing routes Number of lanes Speed limit Grade Shoulder width Traffic characteristics 15
Modeling Approach Improvement Cost Models Construction costs are estimated using unit costs Typically $/square foot for a specified type of project Unit cost data HERS defaults used for roadway, ramp improvements Pontis defaults used for structures Adjustments made for SCDOT conditions based on review by DWA/CECS/Collins 16
Modeling Approach Ranking Combines individual performance metrics into an aggregate result for each segment/interchange Combines metrics of identical units (hours of travel time, cost, number of crashes) A set of ranking schemes has been defined the system administrator can edit the weights associated with each scheme and/or define new schemes Ranks are based on existing conditions, but as alternatives are generated, users can see the new rank that would result from a specified alternative 17
System Implementation Design Considerations Needed to support multi-user access for users within and outside of SCDOT Strong desire for a user-friendly, intuitive interface for the casual user Needed a mapping interface to facilitate viewing and selection of assets 18 Designed a visualization tool for illustrating key design features Mainline orientation, lanes Medians, shoulders Ramp configuration
System Implementation Development Environment Web-based application Developed in Microsoft.NET Microsoft SQL Server database Uses a third party map viewer Intergraph or TransCAD 19 Relies on data imported from Roadway Information Management System (RIMS) AASHTO Pontis Bridge Management System
20 System Implementation Example Segment Alternative Evaluation
21 System Implementation Example Interchange Alternative Evaluation
22 System Implementation Example Ranking
Conclusions HERS-ST models are an extremely valuable resource for a number of application Frequently most practical to take advantage of these models by recoding would be desirable to support a service-based architecture to support increased agency reuse of the core HERS-ST product 23 IIMS next steps Data integration/import enhancement Flexible definition of highway segments Prediction of air pollution costs Support for ranking based on additional criteria
24 Questions