U of M researchers evaluate I-405 tolled corridor in Washington

University of Minnesota researchers recently completed a traffic data and performance analysis of the I-405 tolled corridor in Washington State.

Lawmakers in Washington authorized the creation of express toll lanes (ETLs), including the conversion of some existing high-occupancy vehicle (HOV) lanes to high-occupancy toll (HOT) lanes, in 2011. The lanes opened to traffic in September 2015.

Last year, U of M researchers analyzed traffic data from 2014–2017 to determine where the I-405 ETL facility is working and where it is underperforming. In addition, the team was asked to compare its findings against relevant performance measures contained in state statute.

The evaluation was conducted by CTS Scholar Alireza Khani, assistant professor in the Department of Civil, Environmental, and Geo- Engineering, and Matt Schmit, director of the Regional Competitiveness Institute and adjunct faculty member at the Humphrey School of Public Affairs. Advisory support was provided by CTS Scholars Lee Munnich and John Hourdos.

In a final report submitted to the Washington Legislature in early January, the researchers shared their findings and provided several recommendations for improving the corridor’s performance.

One significant finding is that a statutory speed-related performance measure—that the average speed in the ETL be above 45 mph at least 90 percent of the time during peak periods—was not met. During peak periods, speeds averaged 45 mph and above 85 percent (northbound) and 78 percent (southbound) of the time. However, these percentages are a significant increase over those in the corridor’s former HOV lanes. And although the ETL facility is not meeting the statutory speed requirement, it is increasing corridor throughput. The ETLs are serving 59.2 percent (northbound) and 94.5 percent (southbound) more vehicles than the previous HOV lanes.

Another key finding is that ETL toll rates max out (at the $10 cap) during 15 percent of the peak period. According to the researchers, this is problematic from a traffic management standpoint because the lane volume can’t be managed through pricing once the maximum is reached. In addition, findings indicate that the tolling algorithm is not optimally responsive, and the toll rate is too low as traffic volume builds. Especially during peak periods, the algorithm and pricing isn’t controlling input traffic effectively, which can result in congestion.

Based on their findings, the researchers provided the following short-term recommendations:

  • Improve ETL speed through a more responsive dynamic toll algorithm
  • Improve ETL speed through segmented corridor tolling
  • Move toward an “open access” ETL facility to smooth lane transfer
  • Increase maximum toll rate to reduce ETL breakdown
  • Adjust a.m. peak period times to increase ETL speed

Of the above, the researchers believe that the first two recommendations offer the greatest promise for addressing congestion and improving corridor performance.

“Washington leaders brought in the University of Minnesota to do this evaluation on a sole-source basis because of the controversial nature of this issue in Washington State and our reputation for quality research on congestion pricing and HOT lanes,” Munnich says. “I believe this is a very high-quality study and an example of the best technical and policy research coming from the University of Minnesota.”

For more information about the study and the researchers’ recommendations, download the final report (PDF).

Posted in Economics, Planning, Traffic operations, Transportation funding, Transportation research

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