Incorporating

Travel-Time

Reliability into 

the Congestion 

Management

Process:

An Informational Brief

February 2015
Incorporating Travel-Time Reliability into the Congestion Management Process (CMP)

What is Travel-Time Reliability?

Travel-time reliability is the variation in travel time 

for the same trip from day to day.

Source: Federal Highway Administration

Why Does Reliability Matter?

Data collected from across the United States 

indicate that non-recurring congestion accounts 

for more delay than recurring congestion due 

to capacity constraints. Highly variable or 

unpredictable travel times make it difficult for 

travelers and shippers to plan trips, leading to 

ineffective or counterproductive travel decisions 

that waste time and money.

What Affects Reliability?

Variable travel times tend to originate from 

disruptions on the transportation system. These 

disruptions occur as a result of any number or 

combination of factors such as inclement weather, 

crashes, construction work zones, arena concerts, 

or major sporting events. In turn, they may cause 

unexpected congestion even in areas that don’t 

normally experience congestion.

Why Should Reliability be Incorporated into CMPs?

The CMP is one of the most effective ways to implement reliability performance measures that more closely 

address the concerns of the traveling public. Congestion management plans tend to be updated frequently 

and are focused on monitoring conditions and developing strategies for alleviating congestion. Three major 

factors are driving the current spotlight on travel-time reliability:

Photographs (Top Left and Bottom Left) courtesy of Kittelson & Associates, Inc., Photograph (Top Right) courtesy of iStock (B. Esov)

Customer Expectations. Surveys of the 

traveling public and freight shippers 

repeatedly show that they value 

travel-time reliability more than speed. 

They expect that public agencies will 

provide real-time information and will 

alleviate the effects of disruptions on 

the roadway and transit network.

Roadway Expansion Constraints. 

Funding and space constraints 

increasingly limit roadway and transit 

system expansion. The impetus 

is to use transportation system 

management and operations (TSM&O) 

strategies to make more efficient use 

of the nation’s existing transportation 

system.

Federal Surface Transportation 

Reauthorization Law. The Moving 

Ahead for Progress in the 21st 

Century Act (MAP-21) establishes a 

system-reliability goal for improving 

the efficiency of the national 

surface transportation system. 

CMPs that incorporate reliability 

provide a pathway to developing 

the performance-based planning 

and programming elements that 

aid this national goal by improving 

regional travel. The Federal Highway 

Administration (FHWA) publishes 

guidance and provides workshops to 

assist agencies with identifying and 

implementing best practices with 

regard to federal law.
Examples of Practices

The effects of non-recurring congestion on travel-time reliability can be minimized if the causes are 

identified and plans for addressing the disruptions are developed and implemented. For example, 

incident management plans typically include protocols for the efficient clearance of roadways or rail 

lines and for the provision of dynamic messaging signs to inform and advise travelers. A sample of some 

regions that have begun to address travel-time reliability in their CMPs is highlighted below.

Source: Regional Transportation Commission of Southern Nevada

Photograph (Top) courtesy of iStock (R. Yasick), Photograph (Bottom) courtesy of Kittelson & Associates, Inc.

The Madison Metropolitan Planning Area CMP specifies analysis 

of non-recurring congestion, specifically crashes, non-collision 

incidents, and work zones. It identifies coordination with the 

Wisconsin State Department of Transportation, Dane County, and the 

University of Wisconsin for data and improvement plans.

The Wilmington Area Planning Council’s CMP has identified a 

strategy evaluation process that prioritizes improving roadway 

operations above adding capacity. To that end, the region 

has increased its investment in technologies for monitoring 

traffic conditions with speed detectors and traffic cameras and 

communicating to the traveling public using variable message signs.

The Regional 

Transportation 

Commission of 

Southern Nevada 

inventories and 

archives data on daily 

congestion events, 

travel times, and 

volumes to calculate 

reliability measures 

for most freeways 

in the region. The 

data are also used to 

customize scores and 

rankings that diagnose 

congestion in terms of 

causes.
Performance Measures for Travel-Time Reliability

Reliability can be estimated by looking at travel-time variability. If variability is great, the travel time is 

considered to be unreliable, because it is difficult to generate consistent and accurate estimates for it. If 

there is little or no variation, the travel time is considered to be reliable. The Planning Time Index (95th 

percentile compared to free-flow travel time) is a common performance measure, among others, that use 

indices shown in the Measures of Reliability figure.

MEASURES OF RELIABILITY

The Planning Time Index (PTI) 

is identified in the Highway 

Capacity Manual as one of the 

most intuitive and consistent 

measures for reliability. 

A PTI of 1.5, for example, 

means that a traveler should 

plan for 50% more time for 

their trip compared to light 

traffic conditions for a 95% 

probability of arriving on time. 

Travel Time

Number of Trips

Free Flow

Mean

85th Percentile

95th Percentile

Source: Strategic Highway Research Program, Phase 2

Getting Started

Metropolitan planning organization (MPO) 

staff who would like to incorporate travel-time 

reliability into their CMPs might consider the 

following steps for creating a robust plan:

Update Goals, Objectives, and Performance 

Measures

Assess Data Needs and Availability

Diagnose Causes of Unreliability for

Select Facilities

Evaluate and Prioritize Reliability Strategies

Prepare CMP Update

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2

3

4

5

Resources for MPOs and States 

FHWA-sponsored training workshops and the 

Primer, Incorporating Travel-Time Reliability into 

the Congestion Management Process, are useful 

resources that demonstrate how reliability can be 

integrated into the following CMP actions:

• Developing Regional Objectives

• Develop Multi-modal Performance Measures

• Analyze Congestion Problems and Needs

• Identify and Address Strategies

• Evaluate Strategy Effectiveness

Office of Operations (HOP)

1200 New Jersey Avenue, SE

Washington, DC 20590

www.ops.fhwa.dot.gov

Pub. # FHWA- HOP-14-035

February 2015

Cover photographs courtesy of Kittelson & Associates, Inc.