Md.'s Lesson: Widen the Roads, Drivers Will Come
Washington Post Staff Writer
Monday, January 4, 1999; Page B1
Congestion on Interstate 270 had grown so oppressive by the mid-1980s that Montgomery County transportation director Robert S. McGarry pressed the state to widen it six years ahead of schedule. Maryland responded with $200 million to widen more than a dozen miles, up to 12 lanes in some stretches.
But now, less than eight years after the project was finished, the highway has again been reduced to what one official called "a rolling parking lot." Traffic on some segments already has exceeded the levels projected for 2010.
"I personally thought it would last much longer than this," said McGarry, who left county government eight years ago. "I just didn't in my wildest dreams think it would fill up that fast."
National transportation analysts say it's no surprise: Widened highways generate their own traffic. This phenomenon, called "induced travel," raises urgent questions for the Washington region at a time when area officials are planning to expand other highways and interchanges, such as the Capital Beltway, Interstate 66 and the Springfield interchange.
Although the exact magnitude of this effect is much debated, some studies suggest that induced travel might entirely overwhelm any relief from congestion resulting from new road capacity.
Motorists may decide to make more trips than before, convinced that the wider road will reduce congestion and make each trip quicker. They also may switch from other routes, expecting to save time. And they may abandon mass transit and climb into their cars – all of which put more vehicles on the widened highway.
In the long run, increased traffic also may result from accelerated development encouraged by the improved highway, with new homes and stores drawing more drivers to the area.
"If you make a road wider, it will be a more attractive place to travel and a more attractive place to live," said David Bernstein, a Princeton University professor.
Planners who expect motorists to enjoy the larger roads without confronting additional traffic are "sadly mistaken," he said. "Most planning agencies . . . don't really account for induced demand."
The widening of I-270 from Route 118 to the split north of the Beltway has no doubt had its benefits. As officials had planned, the project, financed mostly with federal money, fostered commercial development within the corridor, such as the blossoming of high-technology firms around Shady Grove. The wider road also put hundreds of acres of affordable new homes in the Germantown area within the reach of middle-class families.
And for part of the last decade, the added lanes took the sting out of rush hour. "We had five years of smooth sailing, which was wonderful," said C. Stephen Poteat, director of the Upcounty Regional Services Center. But he added, "It's become almost as bad again."
Traffic on I-270 runs as high as 210,000 vehicles a day, according to the Maryland State Highway Administration's counts for 1997, the latest year for which figures are available. That exceeds the capacity of 190,000 initially estimated.
Along several stretches, traffic already has surpassed the levels state highway planners forecast for 2010 in their 1984 study of the proposed widening. The highway administration reported that the 1997 volume at Route 28 in Rockville was 193,000 vehicles a day – 2,000 more than the 2010 projection. The volume at Interstate 370/Sam Eig Highway in Gaithersburg was 171,000 vehicles a day – 10,000 more than was forecast.
"With all the lanes that are there, it just doesn't seem to be moving that quickly," said David Palank, a commercial real estate broker from Germantown who has commuted to offices in the District and Bethesda for the last 16 years. "I haven't found any relief at any time. It seems like it was congested and continues to be congested."
Some officials involved with the project, such as former State Highway Administration head Hal Kassoff, attribute the runaway traffic volumes to Maryland's buoyant economy.
"Highways don't cause traffic," said Kassoff, now vice president of highway programs for the Parsons Brinckerhoff Inc. engineering firm. He dismissed the notion of induced travel as "simplistic."
But increasingly, induced travel is a prominent topic in transportation circles. Richard E. Tustian, a former Montgomery planning director who now teaches planning at the University of Pennsylvania, put it plainly: Traffic ultimately expands to fill available road capacity.
"When a road gets built, it has excess capacity," he said. "That, in turn, does attract vehicles to it. If it gives you a faster time, then people will take it, and it fills up."
Just how much it fills up – and how quickly – remains difficult to measure. Mark Hansen, a professor of transportation engineering at the University of California at Berkeley, used statewide California statistics in concluding that new road capacity is almost entirely offset by induced traffic within five years. He found that a 10 percent increase in capacity leads to a 9 percent increase in miles driven. Other researchers say the induced effect, though clear, is not so extreme.
In a study last year, Kevin Heanue, former director of environment and planning for the Federal Highway Administration, stressed that induced travel is not as significant in explaining worsening congestion as other factors, such as a growing population and increasing car ownership.
By widening I-270, Maryland made living in northern Montgomery and Frederick counties a practical choice for many people working in the District, Maryland's inner suburbs and Northern Virginia. Although Germantown already was growing and no longer was the sleepy railroad outpost of 3,000 people it had been as recently as 1970, the road project opened the area to a housing boom that has lifted the community's population to about 70,000.
"People's willingness to live and work in Germantown has been impacted by their ability to move up and down 270," Poteat said.
Under Montgomery's growth policies, approval for development along much of the interstate had been on hold until the highway project got the go-ahead. In the five years before construction began, officials endorsed 1,745 new homes in the area stretching from Rockville to Clarksburg. During the next five years, 13,642 won approval.
The road project not only eased government restraints on growth. It also made the Germantown area a more attractive place for developers to build and a more popular place for home buyers to live, luring them from other locations such as Olney and Centreville.
"You saw a tide of development go forward because of that improvement," said Sidney Kramer, Montgomery county executive from 1986 to 1990.
The new capacity on I-270 also drew vehicles off other desperately clogged roads, in particular Route 355, according to transportation engineers and planners. Although this may have increased the total number of cars, it did provide at least short-term relief to the county's overburdened road network.
And the easier commute on I-270 attracted travelers to the highway who otherwise would have taken Metro's Red Line, analysts said. At a time when population was continuing to climb in communities along the interstate, ridership at the Shady Grove station – which had been growing steadily since it opened in 1984 – dropped during the three years after the new lanes opened.
Officials caution that it's difficult to measure the precise impact on transit because the drop in ridership at Shady Grove also coincided with an economic recession and came after a pair of fare increases. But while Metro lost 1 percent systemwide, Shady Grove's figure plummeted almost 6 percent.
Harry S. Cohen, who helped write a report for the National Research Council on highway expansions, said the lesson of I-270 is that planners must be more willing to consider the effect of induced traffic when evaluating the benefits of proposed road projects.
"At a minimum," he said, "tests should be run using different assumptions about induced travel to see if their investments are warranted."
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