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VDOT, HNTB Corp. work together to subdue "The Interchange from Hell"
Travelers on nearly any interstate in northern Virginias Springfield area know why The Wall Street Journal called it "The Inte
Travelers on nearly any interstate in northern Virginias Springfield area know why The Wall Street Journal called it "The Interchange from Hell." With 14 overburdened lanes mixing three interstates and one state highway together in a 3/4-mile span, Springfields "Mixing Bowl" interchange carries more than double its intended capacity.
Rush hour backups of a mile and more are commonplace on the interchange, located about 15 miles south of Washington, D.C. At the Mixing Bowl, the Capital Beltway (I-495), intersects with I-95, I-395 and Rte. 644. Heavily traveled by local, long-distance and HOV commuters, the route carries an average of 430,000 vehicles a day.
Northern Virginias "Mixing Bowl" interchange also is one of the most dangerous in the state. Traffic merges from both the left and the right sides of the road, and some motorists must merge across four lanes in less than a mile. A recent two-year study revealed that the interchange logged close to 180 accidents a year, making it the most dangerous spot on the 64-mile Capital Beltway.
Problems on the interchange are nothing new. In fact, the term "Mixing Bowl" was first used in reference to the area in 1942, shortly after the Shirley Highway north of Virginia Rte. 7 was constructed as part of the Pentagon road network. In recent years, economic prosperity and an expanding job and population base have brought more people and more cars to the area. Populations have boomed in the area surrounding the Springfield Interchange, which links local residents south of Springfield to such major employment centers as the Pentagon, Pentagon City and Tysons Corner.
In one of its most aggressive highway programs since the Mixing Bowl was created in 1942, the Virginia Department of Transportation (VDOT) is constructing a new interchange on roughly the same ground outside Springfield. The new interchange will have 24 lanes at its widest point, with appropriate barrier separations. Designed to go up as well as out, the system will include 30 ramps, 41 lane miles of roadway and 50 bridges. The bridge types will range from prestressed concrete AASHTO beams to curved steel plate girders. The project will be completed in six stages over a period of some eight years.
Realizing the necessity and the magnitude of the road improvements needed VDOT commissioned HNTB Corp. to conduct a study of the I-95/I-395/I-495 Interchange in April 1992. Research revealed that continued growth in population and employment would place ever-increasing burdens on the regions transportation system and highway network. Within the next 20 years, the population of Washington, D.C.s metropolitan area is expected to grow from almost 4 million to nearly 5 million. In addition, an influx of traffic from outside the region is expected to increase volume on the I-495 Capital Beltway and the immediate vicinity by at least 50% by 2020.
Neighbors are talking
Public acceptance and support for the new interchange was critical given the major inconvenience constructing the roadway would pose. HNTB and VDOT took extraordinary measures from "day one" to get citizens involved, including among other activities the formation of a Citizens Task Force Committee comprising representatives from neighborhood organizations and local businesses. Numerous public information meetings were held, a telephone hotline was set up, newsletters were published and provisions were made to accept written and oral comments throughout the study process.
In the end, public involvement efforts paid off. A final Location Public Hearing was held in January 1994 and attended by some 400 people, but generated very little opposition. This was primarily due to VDOTs willingness to listen to and incorporate the publics concerns as various alternatives were being developed. Approval by the Virginia Commonwealth Transportation Board of the recommended location alternative was received in June 1994.
In September 1994, VDOT authorized HNTB to begin the final design. Preliminary plans incorporated comments raised before and after the public hearings as well as other related issues.
The convergence of the interchanges three major interstates and the publics concern over the burgeoning traffic volume were not the only factors contributing to the complexity of the project.
Design requirements for the project were strict due to environmental requirements of federal, state and local agencies. The project also had to meet noise abatement criteria and the requirements of the amended Clean Air Act of 1990. HNTB conducted further research on these and submitted a final Environmental Assessment, approved by the FHWA in 1994. Additionally, the new interchange needed to make allowances for future transportation system design integration. High Occupancy Vehicle (HOV) connections between I-95/I-395 and I-495 were added to preliminary designs as a means of accommodating integration.
The carpool lanes are already being heavily used each morning and evening along I-66, the Dulles Toll Road and I-95/I-395and their use is steadily increasing. According to VDOT, the number of people carpooling or taking the bus along I-395 has jumped 47.5% since 1998. Officials estimate that carpools handle about 15% of the regions rush-hour traffic.
Initially, 12 design alternatives, including a "no build" option, were considered for the interchange. Computerized travel demand management (TDM) strategies and mass transit in and of themselves also were considered but determined not to be viable alternatives. The new interchange is designed to work with future regional TDM measures and mass transit plans. The number of designs narrowed considerably as public input and the evaluation of such factors as socioeconomic, environmental, cost, constructibility, signage, construction staging, aesthetic and maintenance were taken into account.
Less blinkin time
In the final design, the need to "shoehorn" a new interchange into a diversely populated and highly developed area was a challenge. The selected design separates northbound traffic by destination, keeping local and through traffic mixed without weaving. Southbound traffic is separated by local, through and HOV traffic.
These modifications will cut down on the number of lane changes drivers need to make to get from one road to the next and cars will no longer have to weave from the right and the left sides of the roadway. In reality, though it is actually a bigger "Mixing Bowl," it will be much easier to navigate.
Construction of Phase I was completed in 1998 with subsequent phases following at a rapid pace. Combined Phases II/III were scheduled to be completed in August 2001. Phase IV is currently under construction, while construction for Phase V is scheduled to begin in the near future.