Operational Analysis for Interstate Access Modifications I-405 Corridor Experience
August 15, 2006Karl Westby Ph.D
I-405 Corridor Today
Seattle, WA3+Million Population30-Mile Corridor200,000+ ADT1 HOV and 2 GP LanesHOV’s Used Extensively
Improvement ProjectSeparated HOV LanesHOV Direct Access Interchanges5,000 New Park-and-Ride SpacesTwo Additional Lanes of CapacityMultiple Implementation PhasesRebuild/Construct 25-30 Interchanges
Interstate Access ChangesFHWA Additional Interchanges to the Interstate System
8-Point Access, Interchange Justification Report, Access Point Decision ReportRequires Detailed Operational AnalysisTraditionally Highway Capacity Manual Based CalculationsUnderstand Implications of Access Modifications
Traditional Analysis IssuesTraditional Approach Has Challenges
4,200 Separate Capacity Calculations Required With HCSHOV and HOT Lane Modeling DifficultiesRamp Meter, Complex Weaving DifficultiesBottleneck Relocation Not RealizedResults Difficult to Explain
New Capacity AnalysisVissim Microsimulation Model6 Hour Peak PeriodsEntire 30-Mile Corridor Modeled
25-30 Interchanges170+ Intersections6 Additional Freeways
Largest Vissim Model in U.S.
New Analysis Issues
FHWA Comfort LevelNot HCSLocal Street-Freeway InterfacesData Presentation
New Analysis SolutionsFHWA Comfort Level
Access Analysis for FHWAOver the Shoulder Review of ModelingFHWA National Expertise InvolvementStrictly Followed FHWA MicrosimulationGuidelines
New Analysis SolutionsNot HCS
Comparison Made Between HCS and Vissim ResultsHCS Similar in Simple Freeway AreasHCS Similar in Basic Weaves, Merges/Diverges Vissim Better in Complex Weaves, Merges/Diverges, HOV-HOT Lanes
New Analysis SolutionsLocal Street Freeway Interfaces
Not Possible/Practical to Model Freeway Corridor and Intersections In VissimIntersections Modeled in CorsimLinked Input/OutputAble to Demonstrate Operational Changes of New Access Points
New Analysis SolutionsData Presentation
Temporal Congestion Charts• Doppler Charts• Brain Scans
Ability to Relay Large Amounts of Information in One ChartWell Received by FHWA, Agencies, General Public
Congestion Charts - SpeedNo Action Improvement
360 Calcs Each
Congestion Charts - LOSNo Action Improvement
Congestion ChartsOnly Operational Data Presented in Master IJR DocumentEasy to Understand Local and Corridor Impacts of Access Changes Including New Access PointsAbility to Deal With Real Issue of Bottleneck Relocation.
Long Term ResultsNew Way of Modeling Corridor Operations for Access Management PlansBetter Understanding of Access and Operations LinkagesBetter Tools for Relaying Complex, Large Corridor Performance to Make Informed Decisions
Operational Analysis for Interstate Access Modifications I-405 Corridor Experience
August 15, 2006Karl Westby Ph.D