Measuring Congestion: Learning from Operational Data

Abstract

As transportation agencies develop operations-based approaches to congestion management and carefully weigh system investments in operations as well as capital improvements, new types of performance information and communication are clearly needed. Citizens expect action on traffic congestion and demand performance information that relates to their concerns and is easy to understand. Traditional congestion measurements are based on modeled speed estimates generated from volume and capacity information. They are difficult to communicate, fail to capture subtle changes in real-world system performance, and are inadequate for many aspects of evaluating specific impacts of projects on congestion. The Washington State Department of Transportation (WSDOT), like other transportation agencies, has been grappling with new approaches to using operational data to monitor and measure system performance. This study describes progress the agency has made to date and how this work ties into national efforts. Speed and travel time data derived from the loop detector network on Puget Sound urban freeways are used by WSDOT to measure and communicate realtime travel times on 12 major commute routes. Continued work toward analyzing different types of congestion distinguishes between recurrent congestion caused by inadequate capacity and nonrecurrent congestion caused by incidents, inclement weather, and other factors such as travel to and from major sporting events. The agency also has made progress in measuring what is of most concern to commuters and haulers: travel time reliability.

Network Robustness Index: A new method for identifying critical links and evaluating the performance of transportation networks

“…Bremmer et al (2004) point out that traditional congestion measurements are based on volume and capacity information, but are often inadequate in many cases. Potential problems associated with the V/C ratio are illustrated in the hypothetical and greatly simplified network shown in Fig.…”

“…Each offers important insights into the spatial layout of the physical highway network, the need to address capacity planning and, more generally, transportation planning from a system-wide perspective taking into account network topology. Current infrastructure management practices typically address the complex decision-making required just to manage demand on individual congested portions of the highway network by identifying critical highway segments using localized level-of-service (LOS) measures such as the volume/capacity (V/C) ratio (Bremmer et al, 2004;Dheenadayalu et al, 2004). A V/C ratio greater than one is indicative of congestion.…”

Assessing travel time reliability in transport appraisal

“…These factors are related to non-recurrent delays that address unexpected or unusual congestion caused by unpredictable or transient events. On the other hand, a recurrent delay can be defined as a predictable jam caused by routine traffic volumes (Bremmer et al, 2004). The recurrent delay, thus, is the analysis target of travel time savings in transport appraisal.…”

Travel Time Reliability in Indiana

“…Sources of non-recurrent congestion include accidents, inclement weather, construction and special events. Separating the causes for travel time variability is important in assessing the benefits of improvement projects and cocoordinating efforts to improve reliability (Bremmer et al, 2004).…”