Strategic Highway Research Program 2
Project L07
Identification and Evaluation of the Cost-Effectiveness of Highway Design Features
to Reduce Nonrecurrent Congestion
Ingrid PottsMidwest Research Institute
AASHTO Subcommittee on Design – Annual MeetingJuly 27, 2010
Strategic Highway Research ProgramSHRP 2
• SHRP 2 focuses on applied research in the following areas:
– Safety
– Renewal
– Capacity
– Reliability
What is Reliability?
• Relatively new term; no single definition
• SHRP 2 Project L03 (Analytic Procedures for Determining the Impacts of Reliability Mitigation Strategies) developed a working definition:
– The level of consistency in travel conditions over time
– Measured by describing the distribution of travel times that occur over a substantial period of time (generally one year)
What is Reliability?
• Traditional approach to assessing freeway performance:
– LOS for peak periods
• New way of looking at freeway performance
– Travel-time reliability – What proportion of motorists experience travel times consistent with their expectations?
Reliability Performance Measures
• How much variability in travel time do motorists experience?
• How much buffer time does a motorist need?
• What percent of trips are “on time” or close to “on time”?
Why is Reliability Important?
• Reliability is an important component of roadway performance (and communicating performance to the public)
• Motorists have less tolerance for unexpected delay than for expected delay
• There are costs to motorists associated with planning for unreliable travel times
• Reliability is important to industries that depend on just-in-time deliveries, and trucking companies that serve those industries
• Reliability can be improved by implementing strategies to address nonrecurrent congestion
Nonrecurrent Congestion vs. Recurrent Congestion
• Primary difference is predictability
• Recurrent congestion– Predictable
– Occurs on a daily basis (morning and evening peak periods)
– Level of congestion is fairly consistent and anticipated travel times are more reliable
• Nonrecurrent congestion– Results from random and less predicable events
– Varies from day to day and from one incident to the next
– Creates unreliable travel times that frustrate motorists
Project Objectives
Identify the full range of possible roadway design features to improve travel time reliability and reduce delays due to nonrecurrent congestion
Assess their costs and operational / safety effectiveness
Provide recommendations for their use and eventual incorporation into design guides
Project Scope
Evaluation and assessment of design treatments that:
-Address at least one of the primary causes of nonrecurrent congestion
Traffic incidentsWork zonesDemand fluctuationsSpecial eventsTraffic control devicesWeather
-Directly or indirectly involve geometric designInclusion of all facility types of potential interest
Freeways | arterialsRoadway segments | intersectionsSignalized | unsignalized
Inclusion of all facility types of potential interest
Phases and Tasks
State of Reliability-Related Design Practice
Highway Agency Experience with Design Alternatives
Preliminary Assessment of Design Alternatives
Phase I Interim Report
DataGathering
Assessment of Design Measures
Guideline Development
I-1
I-2
I-3
I-4
Phases and Tasks
Execute Approved Data Collection Plan
Execute Approved Data Analysis Plan
Prepare Phase II Interim Report
DataGathering
Assessment of Design Measures
Guideline Development
II-2
II-3
II-1
Phases and Tasks
DataGathering
Assessment of Design Measures
Guideline Development
Prepare Design Guidebook
Prepare Draft Final Report
Prepare Information
Dissemination Plan
Prepare /Conduct Five Presentations
III-2
III-3
III-1
III-4
What is a Design Treatment?
• Design treatment:
– A highway design feature
• Directly-design related treatments:
– Implemented through physical changes in the highway design that have a direct influence on traffic flow
• Indirectly-design related treatments:
– Not intrinsically highway design features, but have secondary implications related to highway design
Directly Design-Related TreatmentsMedian crossovers
Moveable traffic barriers
Controlled/gated turnarounds
Movable cable median barrier
Mountable/traversable medians
Extra-height median barrier
Portable incident screens
Shoulder-use lanes
Shoulder improvements for vehicle breakdown and storage
Alternating shoulder
Vehicle turnouts
Bus turnouts
Crash investigation sites
Emergency access between interchanges
Ramp widening
Ramp closure
Ramp terminal traffic control
Ramp turn restrictions
Improvements to detour routes
Temporary bridges
Runaway truck ramps
Reduced construction duration
Improved work site access
Snow fences
Anti-icing systems
Indirectly Design-Related TreatmentsContraflow lanes for emergency evacuation
Contraflow lanes for work zones
HOV/HOT lanes
Dual facilities
Reversible lanes
Work zone express lanes
Traffic signal preemption
Queue jump lanes
Traffic signalization improvements
Signal timing systems
Reversible traffic control devices
Ramp metering/flow signals
Temporary traffic signals
Variable speed limit
Electronic toll collection
Over-height vehicle detection systems
Reference location signs
Roadside call boxes
Fog detection
Road Weather Information System
Avalanche warning system
Flood warning system
Wind warning system
Design-Related TreatmentsExamples
• Crash investigation sites
• Extra-height median barriers
• Snow fences
Crash Investigation Sites
Crash Investigation Sites
Crash Investigation Sites
Extra Height Median Barrier
Extra Height Median Barrier
Snow Fence
Phase II
Data Desired:
•Description
•Purpose
•Applicability to nonrecurrent congestion
•Application criteria
• Design criteria
• Examples of use
• Operational effects
• Safety effects
• Costs
Objective:
To assess design treatments for reduction of delay due to nonrecurrent congestion
Traffic Operational Assessment
• Objective: to determine traffic operational impact of design treatments on nonrecurrent congestion
• Application of models from SHRP 2 Project L03
– Freeways in large urban areas
– Peak periods
• Simulation modeling
– Freeways in rural and small/medium urban areas
– All freeways during off-peak periods
Safety Assessment
• Objective: to determine relationship between safety and various levels of congestion
• Three years of traffic operational data (5-min volume and speed data) for freeway systems of:
– Minneapolis/St. Paul, MN
– Seattle, WA
– Los Angeles, CA
• Crash data from FHWA’s Highway Safety Information System (HSIS)
Phase IIIDesign Guidebook
• Treatment assessment for each treatment
– traffic operational and safety effectiveness estimate or methodology
• Treatment selection procedure
• Treatment selection tool
• Full implementation guidance
Questions?