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