An Engineering Feat in 15-Minute Pieces
Washington Post Staff Writer
Sunday, January 3, 1999; Page A21
Construction crews are poised. Massive cranes have rumbled into position. They rise high above this most mammoth of road jobs, ready to hoist some of the heftiest steel girders ever used on an American transportation project: as much as 30 tons each and half the length of a football field.
It normally would take up to a week just to deploy the equipment and material needed to erect each girder. Now, under the glare of construction lights in the hours before dawn, workers signal traffic to halt. A team of crane operators, supervisors and safety personnel carries out a kind of superhighway-sized barn-raising with lightning speed and surgical precision. They have only 15 minutes to get the job done.
That's the scenario engineers and contractors have in mind as they plot how to build the bridge spans in the new Springfield interchange on what will continue to be a working highway intersection and one of the nation's busiest, at that.
Because the Springfield interchange is such a key passage for commuters and interstate truckers alike, shutting it down for construction during the day is unthinkable, transportation officials say.
So instead of using routine highway construction methods such as closing parts of the road for days at a time or directing traffic to alternative routes (there aren't many, in this case) officials will have contractors conduct what amounts to construction fire drills to build the massive new interchange.
Virginia officials will allow contractors to close the intersection of Shirley Highway and the Capital Beltway for only a quarter-hour at a time. During those early-morning spurts of furious activity, the massive beams that will support the huge new interchange will rise.
And as fast as the crews are, they must be equally deliberate. "You don't just pick these things up and jerk them around," said Richard Daugherity, of the Virginia Road and Transportation Builders Association.
The feat of erecting these giant beams is among the many challenges posed by one of the nation's most complicated highway projects ever.
"Certainly, the most complex aspect is building under [conditions of] traffic," said Robert B. Newman, vice president of HNTB Corp., the engineering firm designing the project for Virginia's Department of Transportation. "That's the big daddy of them all. I could come up with a great design, but if you can't build it [during] traffic, it doesn't count at all."
VDOT will prohibit contractors from closing lanes during rush hours and limit any total shutdown to the hours from midnight to 5 a.m. Monday to Thursday.
"The fact of 375,000 cars a day going through that construction site makes it very complex," said John P. Fowler II, a transportation engineer who originally designed much of the Virginia section of the Beltway opened in the 1960s. "It has to be staged in infinite detail. It reverberates through the whole design of the whole complex."
Even if the project were being erected on virgin pasture, it would require some deft design to piece together the 30 ramps, 50 bridges and 41 miles of roadway. But Springfield is no vacant lot. The new interchange has to be constructed in, around, over and under the existing web of highways as well as within a tight circle of homes, businesses and ball fields.
With a torrent of cars expected to continue through the work site and with free space at a premium, engineers and builders face a host of tough questions: Where will contractors find room to store tens of thousands of tons of steel? How will they get access for their equipment? Is there any place to detour cars?
Just finding enough free patches of ground to put down hundreds of bridge supports, for instance, becomes a daunting test of engineering dexterity. One bridge alone the three-quarter-mile elevated roadway carrying traffic through the interchange on southbound Interstate 95 will require 25 of these supports. They're up to 20 feet wide and 7 feet thick. So building the interchange will be like playing a titanic game of Twister.
There's simply not enough open ground amid the existing roads for the concrete footings that often form the base of bridge supports. So HNTB has opted for an approach that requires less free space: the more complicated option of securing the supports by sinking them far deeper into the earth. For each support, the builder will drill as many as four shafts about 70 feet deep, all the way to rock, and then fill them with reinforced concrete.
That concrete will be but a dollop amid all the construction material needed for the interchange. The next two phases alone call for enough concrete to pave 30 football fields six inches deep.
It's not the quantity of material, however, that makes the undertaking unique. It's the design.
By separating local, express and car-pool lanes into their own roadways in a sense creating three distinct but overlapping interchanges the engineers have concocted a project unprecedented in the East. In the entire United States, only Los Angeles now has a freeway junction that braids together so many separate roadways, according to highway consultant Joel Leisch. He is considered the country's leading interchange expert and is the son of the highway engineer who designed the highway network near the Pentagon more than 50 years ago.
The new Springfield interchange will be a massive mesh of ramps, overpasses and bridges, some as high as 100 feet and ranging in length from 130 feet over the Norfolk Southern rail line to three-quarters of a mile on southbound I-95. Assembling all these roadways is like putting together a jigsaw puzzle in three dimensions.
But that's not all. Some neighboring ramps and bridges have to be designed at similar elevations so that cars can be detoured between these roadways as construction is done on them. And they have to be built in a certain order so that higher bridges can be added after lower ones.
The engineers don't have much elbow room. The Springfield interchange actually knots together two separate junctions the Beltway crossroads and the intersection of I-95 with Route 644 (commonly known as Old Keene Mill and Franconia roads) less than a mile to the south. "Either one of these projects without the other is a complex project," said Clifford A. Roberts, a senior highway designer with HNTB.
The proximity of these two interchanges combined with the overall necessity of squeezing miles of roadway into a confined, already built-up area means engineers are hard pressed to develop plans that eliminate sharp curves and avoid making traffic weave, contain room for drainage and give bridges ample clearance without steep grades.
"It's a juggling act," said Martin Pietrucha, chairman of the traffic and highway safety committee for the American Society of Civil Engineers. "There are so many things a designer has to keep in mind. That's part of what makes it so complex."
One HNTB team specializing in signs has spent much of the last two years designing 167 fixed signs at 88 locations as well as 20 variable-message signs meant primarily to inform travelers of congestion ahead. Another team has devoted much of the two years to mapping out the location and power source for 565 light poles.
The HNTB engineers say it's the kind of project that can both crown a career and excite beginning engineers.
"It's like an architecture student wanting to work on the world's largest building," Newman said. "A young student would want to work on something like this."
© Copyright 1999 The Washington Post Company