Traffic Congestion Jumps as U.S. Economy Rebounds

~ Latest INRIX Gridlock Index (IGI) Shows Highest Increase in Traffic Congestion in Two Years

Mar 29, 2013, 10:00 ET from INRIX

KIRKLAND, Wash., March 29, 2013 /PRNewswire/ -- Gridlock in the U.S. has staged a dramatic comeback after two years of post-recession lows. Data from the most recent INRIX Gridlock Index (IGI) shows that traffic jumped by almost 10 percent during February – the largest year-over-year increase recorded by IGI in two years, and a healthy sign of rising economic activity across 100 metro areas.

"Traffic is a great indicator of confidence on the ground," said Bryan Mistele, CEO of INRIX. "People hit the road as they return to work, and businesses ship more freight as their orders increase. IGI shows the pulse of the economy is starting to beat faster."

February's composite IGI score of 6.8 meant that the average trip took drivers in the 100 most populated metro areas 6.8 percent longer because of increased traffic congestion. The IGI's positive turn was echoed by a recent report on the U.S. housing sector. The U.S. Commerce Department reported that February 2013 permits for future construction rose 4.6 percent, reaching the highest level since June 2008.[1] 

The dramatic shift seen in the top-line trend was mirrored by significant jumps in traffic congestion in many of the nation's largest metro areas. For example:

  • Gridlock in Chicago increased over 20 percent from February 2012 to February 2013, hinting that the metro area's slow recovery[2] may be gathering speed.
  • Gridlock in Phoenix increased by almost 19 percent from February 2012 to February 2013, confirming recent decisions made by several retail and casual dining chains to expand in the metro area. [3]
  • Gridlock in New York increased by almost 18 percent from February 2012 to February 2013. This jump is in line with recent news of strong private sector job growth [4].
  • Traffic congestion in Houston increased over 10 percent from February 2012 to February 2013, confirming University of Houston Economics Professor Barton Smith's claim of a recent "boom" in the metro area. [5]

Bucking these trends were San Antonio and San Diego. From February 2012 to February 2013 these metro areas saw traffic decrease by 24 percent and 18 percent, respectively, providing an indication of the impact defense spending cuts that went into effect in March could have on the local economy[6].

INRIX Gridlock Index (IGI) Methodology

The IGI draws data from the INRIX Traffic Data Archive, a historical traffic information database comprised of data collected from hundreds of public and private sources, including a crowd-sourced network of 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 100 of the top metropolitan areas 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 Score 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 the IGI is 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 is greater than 0 is contributing congestion and 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 the leading traffic intelligence platform delivering smart data and advanced analytics to solve transportation issues worldwide. INRIX analyzes real-time data from the largest crowd-sourced traffic network in the world – aggregating data from vehicles and devices all over the world as well as data from hundreds of other sources including traditional road sensors, official accident and incident reports to deliver traffic and driving-related insight, as well as sophisticated analytical tools and services, across six industries in 35 countries.

With more than 200 customers and partners including Audi, ADAC, ANWB, BMW, the BBC, Ford Motor Company, the I-95 Coalition, MapQuest, Microsoft, O2, Tele Atlas, Telmap, Toyota and Vodafone, INRIX's real-time traffic information and traffic forecasts help drivers save time every day. 

[1] U.S. Department of Commerce: Bureau of the Census, "New residential construction in February 2013," March 19, 2013,
[2] Board of Governors of the Federal Reserve System, "Summary of Commentary on Current Economic Conditions by Federal Reserve District," March 6, 2013,
[3] Jim Cross, "Big-name outfits boosting Valley's economic recovery," KTAR, February 26, 2013,
[4] Annie Karni, "City jobs boom bigger than first reported," Crain's New York Business, March 7, 2013,
[5] L.M. Sixel, "Houston-area job growth goes 'boom'," The Houston Chronicle, March 9, 2013,
[6] Sig Christensen, "S.A. Bases Bracing for Impact of Sequester," The San Antonio Express-News, March 2, 2013, and Jonathan Horn, "Why Sequestration Would Sting San Diego," The San Diego Union-Tribune, March 3, 2013,