Back in March, the global traffic-tracking company INRIX put out its annual Traffic Scorecard Report, which said that congestion on Twin Cities area highways and freeways worsened from 2012 to 2013 and that commuters are spending 14 percent more time on the roads.
Two months later, the Minnesota Department of Transportation released the results of its 2013 Metropolitan Freeway System Congestion Report. That study said that congestion on metro freeways was down 1.5 percent from 2012 to 2013.
And then the good folks at TomTom, a Dutch company best known for its mapping and GPS navigation systems, put out its list of U.S. cities with the worst traffic and the Twin Cities came in way down the list at No. 32.
That seemed like good news, yet the same report said that for every hour driven during peak periods Twin Cities drivers experienced delays of 21 minutes. It also said that Twin Cities drivers with an average commute time of 30 minutes spend 59 hours a year stuck in traffic. The INRIX report put that number at 24.5 hours, but noted the commuters spent four more hours behind the wheel in 2013 than they did the previous year.
Of course, almost every time a report on traffic comes out, it makes the headlines. But how do we make heads or tails out of them when they seem to contradict one another?
“They are not necessarily contradictory,” said David Levinson, a professor of civil engineering at the University of Minnesota. “They all have different data, but they are measuring roughly the same thing.”
The differences can start with how the report makers define congestion. MnDOT defines congestion as traffic flowing at speeds less than or equal to 45 miles per hour. TomTom defines it as increased travel time when compared to free-flow conditions.
The data used to compile reports comes from different sources, too. MnDOT uses loop detectors embedded in the pavement while INRIX uses GPS data. Another difference is that the INRIX report looked at traffic volume and delays while MnDOT’s congestion report details the location and percentage of freeways experiencing daily congestion.
Not an exact science
No matter the measuring stick, the reports can provide a snapshot of what is happening on our highways over time. They can tell us that rush-hour traffic seems to be lightest on Friday mornings and hellacious Thursday evenings.
But congestion is not an exact science. It can disappear when bottlenecks are eliminated and form in an instant when a crash or road construction creates gridlock for miles. Or when one of our famous snowstorms hits during the commute. New business or housing developments can alter traffic flow in areas, making roads that were adequate suddenly become packed, creating the perception that congestion is getting worse.
“You might see more this year because the economy has picked up, but generally it has been flat and has been for a while,” Levinson said. “If it gets too bad, people will change their behavior. … There are limits on how bad the congestion can get.”
Data and definitions aside, are our roads getting more clogged? No matter how you slice it, the biggest factor is probably bad where you drive and when.
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