The Corridor Capacity Summary (pdf 2.6 mb) and the detailed Report shows where the capacity constraints exist along the major urban commute corridors; in addition, it details transit ridership along the corridors to assess person throughput. This provides a good understanding on the state of the highway system performance across modes. This 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 parternship with the Unviersity of Washington, transit agencies and metropolitan planning organizations, WSDOT provides a multi-modal analysis of the state highway system in the 2013 Corridor Capacity Report (pdf 5.5 mb).
The 2013 Corridor Capacity Summary provides an overview of corridor performance with a focus on multi-modal person trips. The Summary document debuts double-sided handouts designed to be used as stand-alone documents that tell the multi-modal performance story for the state’s most heavily congested corridors. The 2013 Corridor Capacity Report is a 92-page companion document that provides more in depth analysis and background information behind the measures highlighted in the Summary.
WSDOT introduces new multi-modal measures
With the 2013 edition, WSDOT introduced new performance measures and a new graphical display of information, all with an emphasis on multi-modal and person-based metrics. These measures include park and ride lot utilization, routinely congested highway segments, greenhouse gas emissions, transit ridership, and the costs of congestion for commuters. Highlights include:
- Greenhouse gas emissions from vehicles on the 40 high-demand commute corridors in the central Puget Sound area totaled 12,156 metric tons of carbon dioxide each weekday in 2012, a 3% decline from 2010 daily emissions.
- In 2012, there were nearly 70,600 daily transit riders during peak commute periods on the high-demand corridors in the central Puget Sound area, which translates into 43,800 cars removed from the road daily.
- The per-person cost of congestion for commuters for a round trip to and from work on the I-5 corridor in 2012 ranged from $400 to $1,500 annually. The Everett-Seattle round trip had the highest commute congestion cost on this corridor.
Highlights from the 2013 Corridor Capacity Report
Statewide congestion levels for the past six years (2007 through 2012) indicate 2009 was the least congested year for Washington drivers. The statewide congestion indicators are still below pre-recession levels, as the economy continues to rebound.
- In 2012, each person in the state was delayed in traffic for 4 hours and 30 minutes
- Delay on state highways cost Washington citizens and businesses $780 million in 2012.
- In 2012, per person vehicle miles traveled was the lowest since 1988. On average, each Washingtonian drove 8,303 miles, of which 55% were on the state highway system.
Congestion Performance metrics
WSDOT uses more than 20 different metrics to define and describe statewide congestion trends to provide a comprehensive analysis of system performance. These metrics include delay, travel time, duration of congestion, travel time reliability, maximum throughput travel time index, and new multi-modal measures (see above). For a list of key metrics, please see page 5 of the 2013 Corridor Capacity Report. Thresholds for calculating congestion metrics can be viewed on page 9.
Maximum throughput as the basis for performance analysis
WSDOT ’s goal is to maximize system efficiency by maintaining traffic flow at speeds that allow the greatest number of vehicles to move through a highway segment. Research shows that this maximum system throughput is achieved at 70%-85% of posted speed limit. Maximum throughput speed is a dynamic speed threshold that changes over time: it is affected by many other factors such as highway geometrics, driver behavior, and weather.
WSDOT collects real-time data for 82 commute routes in urban areas around the state. In the central Puget Sound area alone, data is collected from about 6,800 loop detectors embedded in the pavement throughout 235 centerline miles (1,300 lane miles). Similarly, the south Puget Sound area has 128 active data sensors that on 77 centerline miles (270 lane miles). Other urban areas of the state have loop detectors and other technologies used for traffic data collection. WSDOT for the first time uses private sector speed data for Vancouver area commute trip analysis to complement the existing WSDOT data set.
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