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Washington State: Corridor Capacity Report

Posted by Content Coordinator on Tuesday, November 3rd, 2015


WSDOT’s comprehensive annual analysis of multimodal state highway system performance

Making multimodal connections work

Understanding maximum throughput: An adaptation of the speed/volume curveWashington state traffic is growing. Higher employment rates translate into more drivers on the road, which in turn leads to longer commutes and everything that goes with congestion. WSDOT knows that addressing congestion takes a multi-faceted approach involving all partners, which is why the 2015 Corridor Capacity Report (CCR) is designed to help transportation policy makers, planners and engineers implement multimodal capacity opportunities for state highways.

This report apprises WSDOT, the Legislature, stakeholders, educational and research institutions, the media and the public about highway system conditions and how we can work together to reduce congestion. It also supports WSDOT’s Practical Solutions and performance-based planning initiatives by reporting the multimodal capacity within 84 urban commute corridors.

The CCR provides multimodal system analysis, detailing usable capacity on state highways, mass transit, passenger rail and ferries. The report also considers congestion’s impacts on air quality and people’s wallets, providing a more complete picture of how traffic affects the state as a whole.

This report consists of three parts: this Corridor Capacity Report, a data Appendix and an addendum to the Handbook for Corridor Capacity Evaluation. See back cover for more details.

WSDOT expands multimodal analysis

WSDOT’s 2015 Corridor Capacity Report is the agency’s 14th annual statewide analysis of multimodal system performance, and introduces Amtrak Cascades passenger rail performance as its newest addition. In addition, WSDOT is introducing a pilot arterial corridor performance analysis of US 395 in the Tri-Cities region. There is little guidance for detailed performance measurement of arterials.

Based on the positive feedback received on last year’s report, WSDOT continues to fine tune the multimodal and environmental aspects of system performance evaluation from a corridor perspective. For this year’s edition, multimodal capacity is evaluated along with travel time analyses for all major urban areas statewide where data is available. This helps planners take a comprehensive approach to finding solutions that are multimodal in nature.

Congestion on the rise since 2009

Statewide and regional indicators

Although statewide traffic congestion (vehicle hours of delay) has been on an upward trajectory for the past five years, 2014 annual congestion (32.3 million hours) remained 8% below the 2007 pre-recession levels (35.1 million hours). The central Puget Sound region did not follow this 2014 trend and congestion there was 19% higher than pre-recession levels.

  • Of the five monitored freeway corridors in the central Puget Sound region, three (I-5, I-405, I-90) saw congestion increases. Tolling and carpooling reduced congestion on SR 520 and SR 167 by 71% and 24%, respectively, in 2014 compared to 2007 pre-recession levels. (See table and charts on p. 4 of the appendix document).

Vehicle hours of delay increased 4.6% between 2012 and 2014, mirroring the growth in the state’s economy. This delay on state highways cost drivers and businesses $808 million in 2014 compared to $773 million in 2012, about $116 per Washingtonian in 2014 compared to $113 in 2012.

  • This amount of delay was influenced by Washington having more drivers on the road. Passenger vehicle registrations increased 6.9% while licensed drivers increased 7.6% between 2012 and 2014.
  • More drivers in 2014 contributed to a 2.6% increase in the number of vehicle miles traveled (VMT) on all public roadways, up from 56.607 billion in 2012 to a new high of 58.060 billion miles.
  • More drivers also had a hand in a 3.1% increase in the number of vehicle miles traveled (VMT) exclusively on state highways, which hit a new high of 32.177 billion in 2014, up from 31.214 billion in 2012.

Travel times are lower and person throughput is higher in HOV lanes as opposed to SOV (general purpose) lanes (refer to appendix pp. 27-29). A prime example of this is the HOV lane on I-5 at Northgate where travel times were up to 11 minutes more reliable and the movement of people was three times higher than in the adjacent SOV lanes in 2014.

WSDOT Incident Response teams responded to 8.1% more incidents (48,691 total) in 2014 than in 2012, which was accompanied by a 5.8% increase in incident-induced delay.

  • Proactive work by Incident Response teams resulted in $74.1 million in economic benefit in 2014, a 4.9% increase from 2012.

Urban transit

More people are taking buses than before. Transit ridership on urban commute corridors during daily peak periods increased 7.8%, from 104,970 in 2012 to 113,200 in 2014.

  • The number of miles passengers traveled using transit during daily peak periods increased 10.4% statewide, from 1.3 million miles in 2012 to 1.5 million miles in 2014. Transit on I-5, between Federal Way and Everett, moved 56,331 people during peak periods on average weekdays. Without transit it would require five additional SOV lanes to meet the capacity demand on this stretch of I-5.
  • Daily greenhouse gas emissions avoided during peak periods due to transit ridership improved by 17.9%, from 629,673 pounds in 2012 to 742,177 pounds in 2014.


The number of travelers using WSDOT Ferries continues its upward trend as annual ridership increased 4%, up from 22.2 million in 2012 to 23.2 million in 2014. Meanwhile, annual vehicle capacity utilization increased by two percentage points, from 59% in 2012 to 61% in 2014.

  • Annual ferry trip reliability did not change significantly, at 99.5% in 2012 to 99.4% in 2014.
  • Ferries on-time performance dropped one percentage point from 2012 to 94.8% in 2014.

Amtrak Cascades

Amtrak Cascades riders took longer trips but less of them in 2014. While passenger miles traveled increased by 8.3% from 103.1 million miles in 2012 to 111.7 million miles in 2014, ridership declined 3.4% during the same period, from 725,000 to 700,000. Capacity utilization also decreased by four percentage points, from 64% in 2012 to 60% in 2014.

  • Amtrak Cascades annual on-time performance fell by 2.1 percentage points, from 72.1% in 2012 to 70% in 2014.

Download full version (PDF): Washington State Corridor Capacity Report

About Washington State Department of Transportation
The Washington State Department of Transportation is the steward of a multimodal transportation system and responsible for ensuring that people and goods move safely and efficiently. In addition to building, maintaining, and operating the state highway system, WSDOT is responsible for the state ferry system, and works in partnership with others to maintain and improve local roads, railroads and airports, as well as to support alternatives to driving, such as public transportation, bicycles and pedestrian programs.

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