As one would expect for an issue as relevant to our daily lives and economic system as congestion, there are many recently published studies on the issue. This Scorecard expands upon and complements these reports. The following list is but a few of the notable recent reports:

• 2007 Annual Urban Mobility Report (Texas Transportation Institute): http://mobility.tamu.edu/ums/
  
  
• Unclogging America’s Arteries: Effective Relief for Highway Bottlenecks 1999-2004 (American Highway Users Alliance): http://www.highways.org/pdfs/bottleneck2004.pdf
  
  
• Building Roads to Reduce Traffic Congestion in America’s Cities: How Much and at What Cost? (Reason Foundation): http://www.reason.org/ps346/state_by_state_congestion.pdf
  
  
• Freight Performance Measurement: Travel Time in Freight-Significant Corridors (Federal Highway Administration): http://ops.fhwa.dot.gov/freight/freight_analysis/perform_meas/fpmtraveltime/index.htm
  
  
• America’s Most Congested Cities (Forbes Life Magazine): http://www.forbes.com/2008/04/10/congested-commute-cities-forbeslife-cx_mw_0410realestate.html
  
  
• Where the Commuting Nightmares Are (bizjournals): http://www.bizjournals.com/edit_special/56.html
  
  

The Scorecard has some common elements and several unique features

• Common elements
  • The Scorecard adopts the convention of peak period drive time hours of 6 – 10 am and 3 – 7 pm, Monday through Friday as is commonly used
  • The Travel Time Index concept is now a common metric to measure conditions relative to uncongested, free flow situations.
• Unique features
  • This report is based on 2007 data and establishes a process that can lead to very quick turnaround times between the end of the data collection period and the publishing of the Scorecard. Many of the reports utilize data that is many months or years old when published.
  • The Scorecard is completely based upon real data – billions of data points from real vehicles traveling on real road segments. It is not limited by sensor coverage nor is it an interpolation of data
  • This is the first analysis to go to the detailed road segment level nationwide; it is also the first to look in depth by hour and day nationwide

Given the myriad of ways to calculate congestion and the wide range of raw data that is utilized, it is natural that different reports can have different results, rankings and indexes. When comparing the Scorecard and how it has been created, when differences appear between the Scorecard and other reports, it could be due to one or more of the following reasons:

• Many of the reports weight results by traffic volume and/or factor in the number of lanes on roadways; the Scorecard does not
• Travel Time Index calculations are from a road user perspective based on complete random trips, not weighted by volumes, lane miles, or origin/destination weighting
• Travel Time Index values in the Scorecard seem lower than some other studies. This is likely for two reasons:
  1. By using a data driven reference speed instead of a flat speed for free flow, such as 60 mph, results in lower uncongested speeds in most cases, meaning less congestion is calculated for the same average speeds; and
  2. INRIX coverage extends throughout entire metropolitan areas including highways far away from city centers that may contribute little to congestion, lowering the index
• Studies may have different metropolitan areas, or aggregate some regions such as Washington and Baltimore. The Scorecard approach could easily adjust market boundaries to aggregate results differently, but is presently based on the Census CBSA definition.
• The Scorecard is focused on mainline lanes of limited access highways; other studies may include ramps, interchanges and arterials.