New INRIX Gridlock Index (IGI) Shows Traffic Congestion Rising with the Economy

KIRKLAND, Wash., Dec. 10, 2012 /PRNewswire/ -- INRIX, a leading international provider of traffic information and driver services, launched the INRIX Gridlock Index (IGI), a new monthly report that measures the intensity of gridlock in 10 of the largest cities in the US. In October 2012, the aggregate IGI score was 17.6, meaning the average driving trip in these cities took almost 18 percent longer than necessary, due to traffic.

October's traffic congestion data shows that while we are still sharply down from 2010 levels, gridlock has recently been on an upward trend since July 2012. While this may be bad news for the nation's drivers, it may also be a signal that the economy is back on track.

"We believe the IGI is a useful tool, not only for measuring traffic congestion but for also measuring broader economic trends," said Bryan Mistele, CEO of INRIX. "It tells us whether businesses are shipping products, people are going to work and shoppers are going to the mall. What the IGI's telling us now is that we're mired in a stop-and-go economy."

(Photo: http://photos.prnewswire.com/prnh/20121210/SF26306)

According to October's IGI, traffic congestion in these 10 cities was up only 0.75 percent from the previous month, in sharp contrast to August and September increases of 10.5 percent and 12.4 percent, respectively.  Today's release includes data for October 2012, with monthly comparisons dating back to January 2010.

Additional October 2012 IGI highlights include:

• Fewer jobs, less traffic -- Of the 10 cities measured by the IGI, Detroit drivers experienced the least amount of delay in October (an IGI score of 8.5 ) compared to other IGI cities, and also the highest rate of unemployment (10.8 percent).

• Boston was the only city whose IGI score decreased compared to the previous month (from 17.2 to 16.8). Its unemployment rate also crept up from 5.8 percent in September to 6 percent in October.

• New York's IGI score of 21 for October was just shy of its year-to-date high of 21.3. Only drivers in Los Angeles and San Francisco faced worse delays.

• Washington D.C. benefited from having the lowest unemployment rate among the IGI cities (5.3 percent in October), which may have resulted in commuters experiencing some of the worst delays (an IGI score of 17.7).   

• Despite having the highest increase in gas prices as compared to October 2011 (more than 16 percent higher), Los Angeles drivers experienced the worst delays in the country, with the average trip taking them over 30 percent longer (an IGI score of 31.2) due to gridlock.

• Strong employment driven by the tech sector may have offset higher gas prices in San Francisco and resulted in Bay Area commuters experiencing the second worst traffic in the country, after Los Angeles (an IGI score of 27). San Francisco's IGI remained unchanged from the prior month and stood at its highest point for the year.

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 crowd sourced 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.­­

About INRIX
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.

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

SOURCE INRIX