Road Warrior: The Traffic Test

Tom Vanderbilt, author of the book Traffic: Why We Drive the Way We Do (and What It Says About Us), dissects the driving experience, examining everything from what causes congestion to what a driver's marital status says about his or her likelihood to be involved in a crash.

We took some of his assessments and put them to the test by presenting them to local traffic expert, Pei-sung Lin with the Center for Urban Transportation Research at the University of South Florida.

First of all, Pei-sung confirmed Vanderbilt's assertion that "traffic moves smoother if we accommodate late mergers, or even become them."

He says late merging allows two lanes of travel to continue moving for a longer duration than early merging which forces traffic into a single lane before it becomes necessary.

However, he says that the key to keeping traffic moving is for mergers to be aggressive enough to cut into the travel lane that is moving, and drivers in the moving lane must be willing to make way for drivers in the merging lane. Psychologically speaking, drivers in the unending lane tend to be very protective of their position and often times, will not let mergers in, late or otherwise.

Next, Vanderbilt observed that, during rush hour, everyone gets where they are going faster if traffic moves together considerably slower than the speed limit, rather than drivers racing to fill gaps.

Pei-sung confirms this for a couple of reasons:

  1. When drivers stay at a consistent, slower speed as a unit, pockets of intense congestion can be avoided altogether, eliminating "stop-and-go" traffic.
  2. When traffic moves in one consistent wave, there is less erratic driver behavior, and as a result, fewer accidents. Pei-sung does caution drivers against traveling too slowly, saying that it is best to proceed at a speed consistent with the flow of traffic.

Tom Vanderbilt also writes that swerving in and out of lanes actually helps drivers get where they are going faster, but often at a cost of the driver's stress level. He says that maneuvering in and out of lanes saves drivers about four minutes per half hour.

Pei-sung also confirms Vanderbilt's claim that charging for parking eliminates congestion. However, he says that the impact from universal parking costs would be immediate but probably not lasting. While drivers would likely choose to carpool or not to leave the house to start, eventually -- after 10 years or so -- a follow-up study would have to be done as society would have adjusted to paying parking costs. So after the passage of time, drivers would no longer be deterred from driving.

Some other points Vanderbilt makes are:

- Women are responsible for this country's rise in traffic congestion over the past few decades. He says this is because more women have entered the workforce and also because they tend to make more frequent trips to run errands and transport children. However, Pei-sung says there is a difference between incidental congestion and recurring congestion and that men statistically cause more accidents and because congestion is more intense when associated with a crash (especially a serious one), one could argue that men are more responsible for traffic congestion overall.

- In the chapter entitled "Why You Shouldn't Drive with a Beer-Drinking Divorced Doctor Named Fred on Super Bowl Sunday in a Pickup Truck in Rural Montana: What's Risky on the Road and Why," Vanderbilt makes a connection between marital status and crash risk. He states that single people are statistically more likely to be involved in crashes than married people, and while divorced people are less likely to have a crash than people who have never been married, they are still more likely to crash than married people. Pei-sung evaluated this based on the driver's commitments to his family.

- Pei-sung also asserts that teenage boys, who have been named over and over in study after study as the most likely demographic to be involved in car crashes, are more likely to have a crash with passengers in the car, but less likely to crash if the passenger or passengers are female rather than male.

To learn more about Tom Vanderbilt's book, you can log onto To learn more about CUTR or USF's "Center for Urban Transportation Research", log onto


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