Travel Time Reliability

Travel time reliability reflects the variability of travel time. A reliable transportation system dependably provides users with a consistent range of predictable travel times. Travel time reliability is one of the core performance outcomes of many Transportation Systems Management and Operations (TSMO) strategies. TSMO strategies can help meet multiple operations objectives in the reliability area reducing variability and improving buffer and planning times. More than half of the congestion experienced by travelers is estimated to be caused by non-recurring events, such as inclement weather, work zones, special events, and traffic incidents. TSMO strategies address these conditions by systematically identifying and addressing the root causes of delay and variability, thereby making travel times more reliable. By doing this, extra-long delays associated with the non-recurring events are reduced and overall system performance is improved.

Below are some FHWA resources that highlight the basics of travel time reliability and its applicability with TSMO strategies and programs.

• FHWA Travel Time Reliability Measures Website - provides a basic understanding of what travel time reliability is and why it is important.
• FHWA TSMO-related programs - links that highlight various performance measurement activities that include travel time reliability.
• Does Travel Time Reliability Matter? (Primer, Fact Sheet, Flyer, Video) - explores the importance of travel time reliability, the consequences of an unreliable transportation system, and how TSMO can improve travel time reliability.
• TSMO: Getting More from Our Existing System Infographic (PDF 190kb, [8.5”x11”], PDF 194KB [11”x17”], PPTX 3.7MB, PPTX [References at End]) - highlights travel time reliability as one of the benefits of TSMO.
• Urban Congestion Trends - provide annual snapshots of congestion in the United States by summarizing recent trends in congestion using key metrics in travel time reliability, such as travel time index and planning time index.
• Methods to Improve Freight Performance, Reliability, and Bottlenecks Workshop (Report, Presentation) - explores strategies to improve Truck Travel Time Reliability (TTTR) and mobility at truck freight bottlenecks..

SHRP2

Travel time reliability was a major area of research for the second Strategic Highway Research Program (SHRP2), which focused on developing basic analytical techniques, design procedures, and institutional approaches to understand and address the unpredictable congestion that makes travel times unreliable. Products from SHRP2 can be found on the FHWA SHRP2 Reliability website. Below are some of the products that highlight the connection between TSMO and travel time reliability.

• Guidebook: Placing a Value on Travel Time Reliability - Quantifies the benefits of improving travel time reliability to compare TSMO improvements against capacity and safety improvements and help agencies determine which investments are most cost-effective.
• Integrating Travel Time Reliability into Transportation System Management Final Technical Memorandum - describes a methodology supported by SHRP2 reliability data and analysis tools to address the gaps between planning and operations.
• Evaluating Alternative Operations Strategies to Improve Travel Time Reliability - identifies and evaluates strategies and tactics intended to satisfy users’ travel-time reliability requirements of roadways.
• Integrating Business Processes to Improve Travel Time Reliability - explores ways transportation agencies can improve their day-to-day business practices to help address non-recurring traffic congestion and improve travel time reliability.
• Incorporating Reliability Performance Measures into the Transportation Planning and Programming Processes - selecting and calculating performance measures to support the development of key planning products and to help planning, programming, and operations managers apply travel-time reliability to investment decisions. Includes case studies from agencies that have incorporated reliability into their transportation planning processes and reliability assessment spreadsheet tools.
• Incorporating Travel-Time Reliability into the Congestion Management Process (CMP) (Primer, Informational Brief) - provides guidance and potential opportunities for considering travel time reliability in the Congestion Management Process (CMP) and Planning for TSMO program efforts as part of the metropolitan transportation planning process.
• Identification and Evaluation of the Cost-Effectiveness of Highway Design Features to Reduce Nonrecurrent Congestion - explores geometric design treatments that can be used to reduce delays due to nonrecurrent congestion.
• Effectiveness of Different Approaches to Disseminating Traveler Information on Travel Time Reliability - ways to provide travel time reliability information to travelers so the information can be understood and used to influence their travel choices. Includes a Lexicon for Conveying Travel Time Reliability Information of terms designed to convey travel time reliability information to travelers.

SHRP2 also produced products to incorporate travel time reliability into operations and planning data and analysis tools to support TSMO efforts. A set of 18 case studies and four pilot site reports (California, Florida, Minnesota, Washington) highlight findings from transportation agencies that implemented reliability data and analysis tools developed under SHRP2.

• Travel Time Reliability Reference Guide - describes key elements for including travel time reliability evaluation within traffic analysis approaches. The guide is part of an effort by FHWA to update the FHWA Traffic Analysis Toolbox to reflect and incorporate travel time reliability concepts.
• Establishing Monitoring Programs for Travel Time Reliability - describes what travel time reliability is, how it can be measured and analyzed, how to develop and use a Travel Time Reliability Monitoring System (TTRMS), and how to communicate reliability information.
• Analytical Procedures for Determining the Impacts of Reliability Mitigation Strategies - explores predictive relationships between highway improvements and travel time reliability. For example, how can the effect of an improvement on reliability be predicted, and how can reliability be characterized as a function of highway, traffic, and operating conditions? The report presents two models that can be used to estimate or predict travel time reliability.
• Incorporating Reliability Performance Measures in Operations and Planning Modeling Tools - explores the underlying conceptual foundations of travel modeling and traffic simulation and provides practical means of generating realistic reliability performance measures using network simulation models.
• Application of Travel Time Data and Statistics to Travel Time Reliability Analyses - helps practitioners understand the differences in reliability measures derived from different data sources and document the steps needed to turn high-resolution travel time data into reliability performance measures. Covers data sources for reliability; data processing methods for reliability; and creating and comparing reliability measures.
• Addendum to Traffic Analysis Toolbox Volume II: Decision Support Methodology for Selecting Traffic Analysis Tools - reflects up-to-date guidance on incorporating travel time reliability.
• Incorporation of Travel Time Reliability into the Highway Capacity Manual - summarizes work conducted to develop two new chapters for the Highway Capacity Manual 2010 that demonstrate how to apply travel time reliability methods to the analysis of freeways and urban streets.

MAP21 Travel Time Reliability Performance Metrics and Performance-Based Planning

The Moving Ahead for Progress in the 21st Century Act (MAP-21) and the Fixing America’s Surface Transportation (FAST) Act established new performance-based planning requirements for State Departments of Transportation (DOT), Metropolitan Planning Organizations (MPO)MPOs), and providers of public transportation services. These requirements include tracking and reporting key reliability metrics.

• Percent of the Person-Miles Traveled (PMT)person-miles traveled on the Interstate that are Reliable
• Percent of PMT on the non-Interstate National Highway System (NHS) that are Reliable
• TTTR Index Measure

The latest metrics are broken down by state on the FHWA State Performance Dashboard and Reports website. In addition, State DOT/MPO Performance Reports, Dashboards and Plans are also compiled. Given that Performance Measurement is an essential dimension to advancing TSMO programs and capabilities, tracking these key reliability metrics can provide much value for state and local transportation agencies.