Cell phones may cause traffic jams

The science slowly catches up to the intuition about driving distracted.

First, a study at the University of Exeter last month noted that traffic jams are not caused by heavy traffic, but by drivers overreacting. Braking too hard or slowing below certain speeds creates a ripple effect that can put you in an area of abruptly slow traffic with no indication as to why. The key issue:

This model takes into account the time-delay in drivers’ reactions, which lead to drivers braking more heavily than would have been necessary had they identified and reacted to a problem ahead a second earlier.

Why is the time delay key? Because that's what cellphone chatting or other distracted driving does - reduce reaction time.

Motorists talking on the phone drive about two miles per hour more slowly than people who aren’t on the phone...Slower cellphone drivers may be increasing overall commuting times by 5 percent to 10 percent, he calculates, and talking on the phone may increase each daily commuter’s travel time by 20 hours a year....other studies have shown that delayed reaction time related to cellphone use is a safety hazard.

The slow driving held true regardless of use of a hands-free headset:

It’s the talking, not the cellphone, that distracts the brain.

Prediction: the findings will lead to the splendid irony of finding that many Americans phone their destination when they get stuck in traffic to report in and pass the time, perpetuating the traffic jam.