Category Archives: traffic

Are our roads really more congested | StarTribune

Tim Harlow, of the StarTribune’s The Drive column asks if “our roads are really more congested?” and interviewed me:

 

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.

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.”

Minneapolis-St. Paul is No. 16 on the list of America’s worst traffic cities | Star-Tribune

I was interviewed by Mary Lynn Smith of the Star Tribune for the annual INRIX congestion report article:
Minneapolis-St. Paul is No. 16 on the list of America’s worst traffic cities

Depending on the methodology, rankings put the Twin Cities between the 13th- and 16th-largest U.S. metro area, said David Levinson, a civil engineering professor at the University of Minnesota. “The fact that we’re ranked 16th in congestion seems about right,” he said.

Levinson said demographic trends are helping to mitigate road congestion.

“Travel times are declining in the U.S.,” he said. “People are aging. Old people don’t travel as much, and young people don’t travel as much as what young people used to. Fewer kids own cars. The big picture is that that the total amount of travel peaked in the U.S. a few years ago and it’s been declining ever since. We have some ups and downs during any given year depending on the price of the gas and whether the economy is doing a little bit better or not. Certainly [congestion is] more than in 2009 during the depths of the recession.”

Levinson and others are quick to point out that Twin Cities drivers could be dealing with much worse.

In Los Angeles, home to the nation’s most-congested roads, drivers spent 64 hours sitting in traffic, an increase of five hours from the previous year, according to the INRIX study. In Honolulu, the nation’s second-worst city for traffic, drivers sat behind the wheel 60 extra hours last year, while in No. 3 San Francisco it was 56 hours.

And, Levinson points out, there’s more good news for the Twin Cities. The average speed of travel in the metro area is the fifth-highest in the country.

“You sit in traffic at a particular bottleneck, but then when you’re moving on the freeway, you’re driving at 55 mph,’’ he said. “And when you’re driving on arterials, you’re driving at 45 mph, and that’s better than most metro cities.”

I-35W bridge collapse – What happened on August 1st and after

One of the interesting scientific questions that emerges from the tragedy of the I-35W Bridge Collapse is how traffic responds. There are several time horizons for looking at this.
Most immediately are those who are on the link leading up to the bridge. MnDOT’s traffic cameras show the cars turning around on the freeway within seconds of the bridge collapsing, before the dust clears literally. “Video footage of the collapse from Mn/DOT traffic camera 628. 6:05 p.m., Aug. 1, shows an edited two-minute clip from a traffic camera at the south end of the bridge. Initially, the camera is pointed to the south away from the bridge. When traffic comes to a stop, the camera pans to the north where the bridge has just collapsed. (wv file)”. This is a rational response on the part of drivers who don’t know what else may collapse. As my wife says, there are two types of people “those who run towards the meteorite and those who run from it”. Survivors are those who ran from it.
Over the next few minutes and hours, word of the bridge collapse spread. My student Shanjiang Zhu has organized MnDOT’s loop detector data into a movie that shows the 15 minute traffic counts on all the loop detectors in the Twin Cities, comparing that number with the previous Wednesday’s count at the same time of day. Blue indicates lower volumes, red higher volumes. Clearly after the collapse, people heard quickly through various sources (cell phone, variable message signs, radio, etc.), and avoided large swaths of I-35W in the vicinity (which turns blue) and complementary feeder links, while competititve substitute links (Mn 100, I 35E, parts of I-94) saw an increase. We still have to compute how overall traffic volume and Vehicle Kilometers Traveled changed.
Once people were informed, on subsequent days people searched for alternatives. The alternative the first day for some was to avoid driving, but that quickly changed, and different routes became natural substitutes. A second movie compares the counts on the 15 days after the collapse with the average of the previous 8 weeks same day of week (so a Thursday is compared with the eight pre-collapse Thursdays). This illustrates the changes network wide. The
movie is available.
Finally, there may be some longer term adaptations, but we don’t have enough information only one month into the changed situation to know about this yet. With colleagues Henry Liu and Kathleen Harder, we have obtained a National Science Foundation Small Grant for Exploratory Research to look at all of these issues in some more depth.