Travel Time Reliability

Travel time reliability reflects the quality and variability of travel time.  A reliable transportation system dependably provides users with a consistent range of predictable travel times. Transportation system reliability is one of the core performance outcomes of many management and operation strategies. Management and operations (M&O) strategies can help meet multiple operations objectives in the reliability area such as non-recurring delay, reducing the extra-long delays associated with incidents and work zones, and improving transit on-time performance. More than half of the congestion experienced by travelers is estimated to be caused by non-recurring events, such as weather conditions, work zones, special events, and traffic incidents. M&O strategies address these needs by systematically identifying and addressing the root causes of delay, thereby making travel times more reliable.

With the passage of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), transportation system reliability became a major area of research through the second Strategic Highway Research Program (SHRP 2). The Reliability area of SHRP 2 has focused on developing basic analytical techniques, design procedures, and institutional approaches to address the events—such as crashes, work zones, special events, and inclement weather—that result in the unpredictable congestion that makes travel times unreliable. The Transportation Research Board of the National Academies, FHWA, and American Association of State Highway and Transportation Officials work together to implement the results of the SHRP 2 research.