On highway, there’s a breakdown of society
By Beth Teitell
Boston Herald Columnist
Tuesday, August 29, 2006
With the Labor Day holiday weekend coming up fast, let us ponder one of life’s big mysteries:Why do highway traffic jams form out of nowhere, and then, after having caused major agita, and perhaps even advanced some divorces, suddenly disappear?
And, while we’re on the subject, why does a vehicle on the side of the road, with a driver looking under the hood, have the power to cause a three-mile backup?
You’d think that with all the diversions available to the modern motorist - satellite radio, cell phones, books on tape, the blare of the DVD player from the back seat - a late-model sedan idling in the breakdown lane wouldn’t be that interesting. And yet, the backups caused by such attractions are longer than any museum line I’ve ever seen. ‘‘Honey, you’ve gotta get a load of this - it’s a Jetta on the side of the road!”
I was a victim of just such a curiosity-related slowdown last week onI-84 en route to New York City. Don’t get me wrong, I wasn’t hoping for an accident, but after you’ve been inching along for miles, with a preschooler in the back seat who has to go the bathroom ‘‘really, really badly,” you expect - nay, deserve - a legitimate reason for your trouble.
What could cause such a backup, I wondered, too far down the highway to see anything more ahead than a snaking line of cars moving at glacier speed. Terrorist roundup? A Paris Hilton tape playing at a drive-in?
Nope, just the aforementioned Jetta, having a moment.
All through my vacation I thought about that slowdown, so when I got back to work I called Gridlock Sam, the New York transportation engineer famous for originating the term a quarter-century ago.
Sam Schwartz (his real name) explained that roads can enter what traffic engineers call an ‘‘unstable range” (passengers can enter those, too, I’ve found). This happens when the road is close to its capacity, and once it’s in that range, whoa, Nelly, almost anything can cause a problem: a tiny hill, a slight narrowing of the lanes, that stupid car pulled over on the side. The slightest slowdown by one motorist causes the traffic to gel, which in turn sends a shock wave that moves backward through the traffic stream. ‘‘Within minutes it can effect three to five miles,” Schwartz explained.
Once the irritant is removed - the road widens or flattens out, for example - vehicular speed picks up again.
For an engineer, Schwartz has an impressive understanding of the drivers, too: Asked why we care enough to even glance at a car on the side of the road, he had a ready answer: ‘‘We’re glad we’re not the ones pulled over.”
