SECTION: Section 4; Page 4; Column 3; Week in Review Desk
LENGTH: 616 words
HEADLINE: Ideas & Trends: Heavy
No Wonder S.U.V.'s Are Called Light Trucks
BYLINE: By KEITH BRADSHER
ONE of the mysteries of suburban life lies in how traffic jams, long the exclusive bane of cities, have become just as bad or worse at shopping centers and strip malls.
Once the province of city councilmen and mayors, traffic problems, now often referred to as one of the evils attendant on "sprawl," have grown sufficiently pervasive that they have begun attracting the attention of presidential candidates like Al Gore.
Little noticed in the hand-wringing and finger-pointing is an intriguing new debate among civil engineers over whether traffic is actually made worse by changes in the kinds of vehicles that Americans drive.
The question they are trying to answer is whether increasingly popular -- and ever larger -- sport utility vehicles, pickup trucks and minivans clog intersections and slow traffic.
One of the first academic papers on the issue has just been written for the annual conference of the Transportation Research Board, part of the National Academy of Sciences.
The paper's authors, Kara M. Kockelman, the Clare Boothe Luce Professor of Civil Engineering at the University of Texas at Austin, and Raheel A. Shabih, one of her graduate students, used a video camera with a computerized stopwatch to time thousands of vehicles as they traveled through two large intersections with stop lights.
The researchers found that motorists tended to follow so-called light trucks -- sport utility vehicles, pickup trucks and minivans -- at a greater distance than cars.
When sport utilities, pickups and minivans were the first in line as the light turned green, they also tended to accelerate more slowly than cars, probably due to their greater weight.
Apparently, these driver tendencies, combined with increased vehicle size, did in fact reduce the number of vehicles that could cross an intersection during each green light, contributing to gridlock.
The researchers calculated that for traffic traveling straight through an intersection, a large sport utility vehicle took as much space as 1.41 cars. A minivan took as much space as 1.34 cars, a pickup was equal to 1.14 cars and a small sport utility vehicle equaled 1.07 cars.
"People shy away from these things," Professor Kockelman said. "They really eat up a lot of space."
Professor Kockelman predicts that traffic jams will worsen significantly as a result, a problem exacerbated by consumer preferences in automobiles. Annual sales growth for sport utility vehicles peaked in 1996, while sales of pickups and minivans have been leveling off, but their presence as a percentage of all vehicles on the road will climb for many years to come. Sport utilities, for example, still make up only 7 percent of the vehicles on the road, but are 17 percent of new automobile sales.
Other civil engineers, while intrigued by the research, are less certain of its significance. They suggest, for example, that one reason minivans, in particular, may be slow to accelerate at lights is because they are frequently driven by cautious people.
Road engineers say they aren't ready to consider modifying streets or changing the timing on traffic lights because of S.U.V.'s just yet, but they too are picking up signals that life on the road is getting rougher.
Hugh Greechan, the design director of the Westchester County Department of Public Works, does admit that he too has had difficulty making it through short green lights when trailing bigger automobiles.
"If you have three cars in front of you, you'll
get through, if you have two sport utility vehicles in front of you, you'll
get through," Mr. Greechan said. "But if you have three sport utility vehicles
in front of you, you won't get through."
LOAD-DATE: January 16, 2000