Latest INRIX Gridlock Index (IGI) of Road Traffic Congestion Mirrors Slowly Improving US Economy
Data through November 2012 show a continued increase in overall traffic congestion
Kirkland, Washington – January 7, 2013 – The November 2012 aggregate score for the INRIX Gridlock Index (IGI), a monthly measurement of road traffic congestion in 10 of the largest U.S. metropolitan areas, is 17.7, meaning that gridlock in these cities made the average driving trip 17.7 percentlonger than necessary. Published by INRIX, a leading international provider of traffic information and driver services, the latest IGI score shows a sluggish yet enduring rebound in national traffic congestion aligned with the U.S. economy’s slow recovery. At 17.7 the IGI score for November 2012 is only slightly above October’s score of 17.6, but rising well above its historic low-point of 14.04, reached in July 2012.
“The good news is that IGI continued to show signs of an economic recovery. However, it’s less robust than we all would have liked, or expected, as we head into 2013,” said Bryan Mistele, CEO of INRIX. “In fact, some of the lower IGI scores we saw from last November are flashing yellow warning lights – for these local economies and possibly for the nation as a whole.”
Several metropolitan areas experienced month-over-month decreases below the aggregate level for the U.S.:
• Atlanta’s IGI score decreased from 11.7 in October 2012 to 11.1 in November 2012, providing a precautionary note to the University of Georgia Terry College of Business Dean Robert Sumichrast’s recent prediction that the state will outpace national economic growth in 2013.
• Chicago’s IGI score decreased from 15.4 in October 2012 to 13.4 in November 2012, aligned with a slowdown also seen in the University of Illinois’ November Flash Index, which measures Illinois’ growth rates in corporate earnings, consumer spending and personal income.
• Detroit’s IGI score decreased from 8.5 in October 2012 to 6.6 in November 2012, and was the lowest of the Index’s 10 cities during the same period. November’s data confirm the city’s consistent place as an IGI laggard, highlighting its deep-seated economic issues.
The mixed economic picture captured in the November 2012 IGI is all the more notable given the backdrop of lower national gas prices in recent months.
While headline unemployment rates in IGI’s 10 metropolitan areas also have declined, the high number of discouraged workers nationwide (979,000 in November 2012) may exert downward pressure on overall traffic congestion.
Other highlights from the latest IGI release:
• New York’s November 2012 IGI score was up 20% over the previous month, possibly reflecting a rebound from the reduced access seen in the aftermath of Hurricane Sandy.
• A November 2012 IGI score of 17.2 shows that Boston is regaining the ground it lost after dropping from 17.23 in September 2012 to 16.8 in October 2012. Like all of the cities in the IGI, it has yet to retain the highs last seen in 2010.
• Dallas’ November 2012 IGI score of 11.6 was little changed from its October 2012 score of 11.7, remaining stable in the face of the relatively upbeat assessment seen in the last quarterly survey of the Dallas Regional Chamber.
• San Francisco’s November 2012 IGI score saw a very slight decrease month-over-month from 27 to 26.9. The tech-hub’s score remained well above its 2012 low-point of 18.7 (observed in July).
• Los Angeles once again took top honors with the highest IGI score in the nation of 31.6, meaning that gridlock forced its drivers to endure an increase of almost 32% in the duration of their average driving trip.
• Miami and Washington D.C. are the only IGI cities whose scores have increased every month since July 2012.
IGI Scores: November Averages
Percentage increase in the duration of the average road trip due to gridlock
Metro Area November 2010 November 2011 November 2012
Atlanta 16.29 11.91 11.10
Boston 18.34 15.67 17.20
Chicago 18.59 15.27 13.40
Dallas 13.51 11.05 11.60
Detroit 8.07 7.64 6.60
Los Angeles 38.42 29.46 31.60
Miami 16.79 15.04 15.10
New York 25.42 21.71 25.10
San Francisco 26.01 26.30 26.90
Washington D.C. 23.45 18.86 18.00
Month Average: 20.49 17.29 17.70
IGI Scores: November Year-to-Date Averages
Percentage increase in the duration of the average road trip due to gridlock
Metro Area November YTD 2010 November YTD 2011 November YTD 2012
Atlanta 18.46 14.73 11.00
Boston 22.37 19.41 14.80
Chicago 23.80 18.23 14.00
Dallas 16.07 13.24 10.70
Detroit 14.53 10.43 7.20
Los Angeles 39.90 31.85 28.90
Miami 20.69 17.26 14.00
New York 28.40 24.35 19.70
San Francisco 27.25 25.33 23.50
Washington D.C. 25.09 20.20 16.50
Month YTD Average: 23.66 19.50 16.00
INRIX Gridlock Index (IGI) Methodology
The INRIX Gridlock Index draws data from the INRIX Traffic Data Archive http://scorecard.inrix.com/scorecard/, a historical traffic information database comprised of data collected from hundreds of public and private sources, including a crowdsourced network of approximately 100 million vehicles and mobile devices.
Drawing on almost three years of trend data, INRIX has developed methods to interpret real-time traffic data to establish monthly and annual averages of traffic patterns in all major U.S. cities. These same methods can aggregate data over periods of time to provide reliable information on speeds and congestion levels for given segments of roads. Using this proprietary data collected from INRIX’s extensive network, the IGI analyzes and measures traffic trends in 10 of the top metropolitan markets in the U.S. The metropolitan areas used in the IGI are defined by the Core-Based Statistical Areas (CBSA), as determined by the United States Census Bureau.
There are two key building blocks for the analysis used in the IGI:
• Reference Speed (RS): An uncongested “free-flow” speed is determined for each road segment using the INRIX Traffic Data Archive.
• Calculated Speed (CS): Speed data from the INRIX Traffic Data Archive is analyzed to determine the “calculated speed” for each 15-minute period of each day, for each road segment every month (e.g. Monday from 06:00 to 06:15 for April 2012). Thus, each road segment has 672 corresponding calculated speed values per week – representing four 15-minute time windows for each hour of the day, multiplied by seven days in a week.
To assess congestion across a metropolitan area, INRIX utilizes and adapts several concepts that have been used in similar studies and previous INRIX analyses.
The IGI represents the barometer of congestion intensity. For a road segment with no congestion, the IGI would be zero. Each additional point in the IGI represents a percentage point increase in the average travel time of a commute above free-flow conditions during peak hours. An IGI of 30, for example, indicates a 20-minute free-flow trip will take 26 minutes during the peak travel time periods, which is a 6-minute (30 percent) increase over the free-flow travel time.
For each road segment, an IGI Index is calculated for each 15-minute period of the week, using the formula IGI= (RS/CS) – 1.
“Drive Time" Congestion: To assess and compare congestion levels year to year and between metropolitan areas, only “peak hours” are analyzed. Consistent with similar studies, peak hours are defined as the hours from 06:00 to 10:00 and 15:00 to 19:00, Monday through Friday – 40 of the 168 hours of a week.
For each metropolitan area, an overall level of congestion is determined for each of the 40 peak hours by determining the extent and amount of average congestion on the analyzed road network. This is computed as follows, once IGI's are calculated for each road segment:
• STEP 1: For each of the 40 peak hours, all road segments analyzed in the CBSA are checked. Each road segment where the IGI > 0 is contributing congestion and it is analyzed further.
• STEP 2: For each road segment contributing congestion, the amount the IGI is greater than 1 is multiplied by the length of the road segment, resulting in a congestion factor.
• STEP 3: For each 15-minute period, the overall metropolitan area congestion factor is the sum of the congestion factors calculated in STEP 2.
• STEP 4: To establish the metropolitan IGI for a given 15-minute period, the metropolitan congestion factor from STEP 3 is divided by the number of road miles analyzed.
• STEP 5: A peak period IGI is determined by averaging the 15-minute indices from STEP 4.¬¬
INRIX® is a leading traffic intelligence platform delivering smart data and advanced analytics to solve transportation issues worldwide. INRIX crowd sources real-time data from approximately 100 million vehicles and devices to deliver traffic and driving-related insight, as well as sophisticated analytical tools and services, across five industries in 35 countries.
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Media ContactJim Bak