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?