WSDOT continues to deploy innovative solutions and projects to reduce congestion as part of the agency’s Moving Washington strategies. The 2012 Annual Congestion Report (pdf 3.75 kb), shows that congestion on Washington's highways between 2009 and 2011 has in many ways mirrored both the economic recession and the recovery.The report includes analysis of Before and After results from projects deployed within WSDOT's Moving Washington strategies: Operate Efficiently, Manage Demand, Add Capacity Strategically.
Trends in this year's report, which analyzed data from 2009 and 2011, show that most congestion performance metrics for 2011 are below 2009 levels, but fairly even with 2010.
Highlights from the 2012 Congestion Report
The 2012 Congestion Report provides in-depth analysis of 52 central Puget Sound and two Spokane commute routes as well as information on statewide transportation system performance. Selected highlights include (comparing 2011 vs. 2009, 2010):
• Vehicle miles traveled (VMT) on all public roads shows that the average Washingtonian drove 50 fewer miles in 2011 than in 2009 and 88 fewer miles than in 2010. Similarly, for VMT exclusively on state highways, Washingtonians drove 69 fewer miles in 2011 than in 2009 and 76 fewer miles than in 2010.
• In 2011, per person VMT tied with 2008 for the record low of 8,417 on all public roads and 4,648 on state highways. This does not mean the VMT is at its lowest, but rather the 2011 ratio between VMT and statewide population is the lowest recorded in the past 24 years.
• The 2011 total VMT on Washington public roads took a 0.4% dip from 2010 levels while state highways took a 1% dip.
• The total VMT in Washington in 2011 were back to 2009 levels: All public roads VMT saw 0.9% increase, while state highways VMT showed no change compared to 2009.
• In 2011, delay on state highways when measured at maximum throughput speed was 16% greater than in 2009 and 3% greater than in 2010. Similar trends were seen when the delay metric was calculated at posted speed limits.
• Each Washingtonian spent 14% more time in traffic in 2011 compared to 2009, and 2% more than in 2010 when measured at maximum throughput speed. Again, the person delay trends were similar when calculated at the posted speed threshold.
• Five-year statewide delay data shows that 2009 was the least congested year for the state.
• In 2011, cost of delay to drivers and businesses in Washington is estimated as $780 million when measured at maximum throughput speeds and $1.142 billion when measured at posted speeds.
• Vehicle hours of delay on major Puget Sound corridors increased by 9% between 2009 and 2011 and held steady between 2010 and 2011.
• Most of the 40 high demand commute routes saw modest changes in travel times (less than two minutes longer or shorter than in 2009).
• Forty out of 46 high occupancy vehicle (HOV) routes saw improved travel times in HOV lanes compared to their general purpose (GP) counter parts. The remaining six routes showed no significant difference.
• All of the 46 HOV lanes were more reliable in terms of travel times than their GP counter parts, often by a significant degree.
• In 2011, the annual average Maximum Throughput Travel Time Index (MT3I) for Puget Sound area commutes (1.35), increased by 3.8% when compared to 2009 (1.30) and decreased by 1.4% when compared with 2010 (1.37).
• Moving Washington projects are being implemented at strategic locations on the state highway system to help fight congestion and the following Before and After case studies demonstrate results.
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.
Congestion Performance metrics
In order to provide a comprehensive analysis of system performance, WSDOT uses more than 20 different metrics to define and describe congestion trends in Washington. These metrics include delay, travel time, duration of congestion, travel time reliability, and maximum throughput travel time index. For a list of key metrics, please see page 13 of the 2012 Congestion Report. Thresholds for calculating congestion metrics can be viewed on page 15.
WSDOT analysis primarily uses measured, archived, real-time data, collected across the state using more than 6,800 in-pavement induction loop detectors. Other data capture technologies include Automated License Plate Reader (ALPR), moving test vehicles, and tolling transponder data. In addition, this report also uses some Highway Performance Monitoring System database to calculate the statewide performance metrics where loop data does not exist. Other data sources used in this report include economic data, collision data, and transit ridership data, to name a few. Overall, WSDOT performs extensive data quality control on all data sets used in this analysis.