Does Travel Time Reliability Matter? - Primer

Executive Summary

The transportation system is effective only if it is reliable. With the right mix of strategies to manage traffic and demand and respond to disruptions, road users can better predict travel time and reach destinations on time.

Travelers depend on the U.S. transportation system every day to get to work and to special events, acquire and deliver goods and services, and respond to emergencies. If the system operates as expected and enables travel within a predictable amount of time, we can rely on it. When it doesn’t, we can’t. This lack of reliability affects our health, jobs, families, relationships, cost of consumer goods, emergency response times, and the amount of time we have for other things. So, does travel time reliability matter? Yes. But what is travel time reliability really, what are the impacts of unreliable travel time, how do we measure it, and what can be done to improve reliability? These are the key questions addressed in this primer.

This primer starts by explaining the need to invest in reliability. Next, it defines travel time reliability, factors that affect reliability, and the relationship between reliability and congestion. From there, an explanation of how to measure and quantify reliability is provided, including various metrics and types of data that can be collected using various methods. The primer then describes the cost of an unreliable system to businesses, the traveling public, and local governments and how lack of reliability can impair safety and security. Lastly, practical strategies and actions for creating and maintaining a reliable transportation system are provided, along with case study examples of successful State and local efforts. This information is intended to assist transportation systems management and operations (TSMO) professionals in designing their own approaches to improving travel time reliability in their area and to help them better understand and explain travel time reliability to gain support for their efforts.

This primer is based on information from an extensive literature search and review, which located national and international publications addressing the importance of reliability, consequences of unreliability, and successful solutions to improve reliability in transportation and other industries. In addition to information from scientific journals and conferences, a wealth of information was collected from Federal Highway Administration (FHWA) and Second Strategic Highway Research Program Reliability Solutions publications.

Key findings from the literature review on travel time reliability that are presented in this primer include the following:

1. Travel time reliability is a relatively new concept and is being introduced as an additional factor in transportation planning and management.
2. An unreliable transportation system has adverse effects on the social, economic development, environmental, safety, health, and other aspects of communities and jurisdictions.
3. Improving travel time reliability requires integrating business processes as well as organizational and institutional changes in transportation agencies and among other stakeholders. The use of technology, better communication among agencies training of first responders, and the changing of travel data into intelligence are a few strategies that can improve travel time reliability.
4. Plentiful information on travel time reliability is available to transportation professionals; however, educating decisionmakers and communicating to them the value of investments in improving reliability remains a challenge.

Additional resources that complement this primer, including presentation slides, a printable factsheet, flyer, and short video, are available online from the FHWA TSMO website (see https://ops.fhwa.dot.gov/tsmo/).