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21st Century Operations Using 21st Century Technologies

Incorporating Travel-Time Reliability into the Congestion Management Process (CMP): A Primer


Travel-time reliability is an important element of congestion that historically has not been considered as part of the Congestion Management Process (CMP). Taken on average, and as a whole across the United States, non-recurring congestion accounts for more delay than recurring congestion. Non-recurring congestion is caused by disruptions, such as traffic incidents, weather, road construction and maintenance, poor signal timing, and/or special events.

Three major factors are driving the focus on travel-time reliability:

Roadway expansion constraints

Physical and other constraints make traditional capacity improvements increasingly difficult. Transportation system management and operations strategies (TSM&O), designed to address reliability are usually easier to implement and can be installed more quickly than traditional capacity improvements.

Customer expectations

The value of travel-time reliability is being increasingly recognized as a key aspect of transportation performance to system users. For personal travel, travel to support commute trips, and most importantly travel that affects freight operations, research is showing that travel-time reliability is valued at a level comparable to, and in some cases more than, average travel time.

Federal surface transportation reauthorization law

Moving Ahead for Progress in the 21st Century Act (MAP-21) establishes a system reliability goal for the national transportation system with an emphasis on performance-based planning and programming (PBPP) to ensure achievement of that goal.

This primer identifies opportunities for incorporating travel-time reliability into the CMP. It is intended for use by state and metropolitan planning organization (MPO) planners as well as by operations managers and analysts who are planning and programming transportation investments to better manage congestion in urban areas. The primer illustrates how advances in probe data and system detection technologies, as well as new analysis tools developed under the second Strategic Highway Research Program (SHRP 2) [1] program, can enable reliability analysis to be incorporated into the CMP.

The primer is organized as follows:

Chapter 1. Introduction

Defines travel-time reliability as well as the impetus for and value of incorporating it into the CMP.

Chapter 2. How to Incorporate Reliability into the Congestion Management Process

Focuses on key points in the CMP where travel-time reliability could be added to create a more robust plan. This includes:

  • Objectives and performance measures
  • Diagnosing causes of reliability problems
  • Generation of reliability strategies
  • Evaluation of reliability strategies
  • Monitoring of reliability outcomes

Many of the data sets and tools for evaluating reliability are described in this section, including the use products developed as part of SHRP 2.

Chapter 3. Getting Started

Provides a checklist for agencies to use for getting started on incorporating reliability into their CMP.

Chapter 4. Model Congestion Management Plan

Demonstrates specific sections of current CMPs in which reliability has been incorporated.

Chapter 5. Summary

Recaps the motivation for the Federal Highway Administration (FHWA) to support the development of robust CMPs.

Chapter 6. References

Details the source of materials used for this primer's development.


Provides a brief overview of the CMP and reference to the "Congestion Management Process: A Guidebook" for those who are unfamiliar or need a refresher on the process.


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