WSDOT accountability report replaces congestion with corridor capacity

By Robbie Webber

Washington State Department of Transportation has been rightfully proud of their accountability and transparency with their quarterly Gray Notebook, which details system performance and project delivery. As part of that, they have issued an Annual Congestion Report. But the 2013 report has a new name and a new emphasis. Instead of highlighting congestion, the 2013 Corridor Capacity Report focuses on capacity across all modes. Rather than measuring just motor vehicle throughput, it turns its attention to moving people, regardless of mode.

The full report and summary highlight the importance of a multimodalism and explains how transportation system efficiency would improve if travelers made better use of available capacity across all modes of transportation. Another change makes the metrics more personal and easily understood by the public. Instead of giving aggregate numbers for the state, the report gives per person measures for fuel wasted, greenhouse gas emissions, and the cost of being stuck in traffic on the most heavily used corridors. Infographics make much of the information more accessible to the average Washingtonian.

The report also focuses on the most traveled commute routes in the urban areas of the state, i.e., central and south Puget Sound, Vancouver, Spokane, and the Tri-Cities. In partnership with the University of Washington, transit agencies, and metropolitan planning organizations, WSDOT provides a multimodal analysis of the state highway system. But instead of simply documenting congestion or suggesting highway infrastructure solutions, the report emphasizes that congestion can be mitigated by using the capacity of other modes.

In addition to standard highway measures such as congestion and highway capacity metrics, the 2013 edition contains the following new congestion performance measures:

  • Commute congestion cost, emphasizing that traveling during peak hour wastes fuel and time;
  • Greenhouse gas emissions during peak hour per person and how much could be avoided by using transit;
  • Transit ridership during peak hour between commute origin and destinations and what percent of transit capacity is being used;
  • Park and ride capacity and average percent of capacity being used; and
  • Routinely congested segments, where traffic demand reaches capacity on at least 40% of weekdays annually.

The report also recognizes that highways are not necessarily operating at their maximum efficiency or throughput when all vehicles are moving at 60 mph. Research shows that maximum system throughput is achieved at 70%-85% of posted speed limit. WSDOT has chosen to measure maximum throughput and set the goal of maintaining traffic flow at speeds that allow the greatest number of vehicles to move through a highway segment—rather than whether drivers can move at the speed limit or the roadway is free flowing during peak hour.

With per capita vehicle miles traveled down 202 in 2012 from the 2010 levels—the lowest since 1988—WSDOT recognizes that residents want more transportation options and are expecting performance measures for all modes. The Corridor Capacity Report provides the data to look at all those options.

Robbie Webber is a Senior Associate at SSTI.