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TTI Data - Chicago - Performance Measure Summary There are...

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1 Performance Measure Summary There are several inventory and performance measures listed in the pages of this Urban Area Report for the years from 1982 to 2005. There is no single performance measure that experts agree “says it all.” The best comparison of congestion levels and trends is done between regions of similar size, over several years, and with a few measures of congestion aspects. Examining a few measures over many years reduces the chance that data variations or the estimating procedures may have caused a “spike” in any single year. A few key points should be recognized by users of the Urban Mobility Report data. Use the Trends – The multi-year performance measures are better indicators, in most cases, than any single year. ( 5 years is 5 times better than 1 year ). Use several measures – Each performance measure illustrates a different element of congestion. ( The view is more interesting from the top of a few measures ). Compare to similar regions – Congestion analyses that compare areas with similar characteristics (for example population, growth rate, road and public transportation system design) are usually more insightful than comparisons of different regions. ( Los Angeles is not Peoria ). Compare ranking changes and performance measure values – In some performance measures a small change in the value may cause a significant change in rank from one year to the next. This is the case when there are several regions with nearly the same value. ( 15 hours is only 1 hour more than 14 hours ). Consider the scope of improvement options – Any improvement project in a corridor within most of the regions will only have a modest effect on the regional congestion level. ( To have an effect on areawide congestion, there must be significant change in the system or service ). Comparison of Several Key Mobility Performance Measures Very Large Group – over 3 million population urban areas Urban Area Delay per Traveler Travel Time Index Total Delay 1982 to 2005 Delay per Traveler Total Delay New York-Newark, NY-NJ-CT L 0 H+ 0 F+ Los Angeles-Long Beach-Santa Ana, CA H+ H+ H+ S F+ Chicago, IL-IN L H+ H 0 F+ Miami, FL L 0 L 0 0 Philadelphia, PA-NJ-DE-MD L- L- L- S- S- Dallas-Fort Worth-Arlington, TX H L L F+ F Washington, DC-VA-MD H 0 L F+ S- Atlanta, GA H L L 0 S- San Francisco-Oakland, CA H H L F S- Boston, MA-NH-RI L L- L- 0 S- Detroit, MI 0 L- L- S S- Houston, TX H 0 L- S S- Phoenix, AZ L L L- S- S- Seattle, WA L- L- L- 0 S- 0 – Average congestion levels or average congestion growth H Higher congestion; H+ Much higher congestion; F Faster congestion growth; F+ Much faster growth L Lower congestion; L- Much lower congestion; S Slower congestion growth; S- Much slower growth
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2 Performance Measures and Definition of Terms Travel Time Index – A measure of congestion that focuses on each trip and each mile of travel. The ratio of travel time in the peak period to travel time in free-flow. A value of 1.30 indicates a 20-minute free-flow trip takes 26 minutes in the peak.
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