Fast Track for Commuters

Anchorage Interchange Project Eliminates Traffic Bottleneck
August 11, 2010

Bottlenecks are an anathema to traffic engineers and commuters alike. A major Anchorage bottleneck on a route that sees upwards of 50,000 trips per day is being eliminated with the construction of a grade-separated interchange that replaces a signalized intersection at the Glenn Highway and Bragaw Street.

The $30-million project also includes widening almost one mile of the westbound Glenn Highway from two to three lanes. The design-build venture is the collaborative effort of prime contractor Wilder Construction Co. and Dowl Engineers. The Alaska Department of Transportation and Public Facilities issued the contract in May 2007 with a project completion date scheduled for fall 2008.

The project included demolition of some existing homes and business structures to make way for the interchange that includes a multispan bridge that will carry Bragaw Street traffic over the Glenn Highway. Part of the early work entailed removal of an existing pedestrian overpass and the relocation of existing utilities, including water, sewer, electrical, gas, and telecommunications cable.

It was during the excavation for new utilities through the footprint of the demolished buildings that soil contamination was encountered at the site of a former auto repair facility. Wilder gave the job of contaminate identification and remediation to Anchorage-based CEI, the demolition contractor already on board as a subcontractor.

"CEI is also a specialty contractor in dealing with hazardous material and abatement. They assisted in the contaminate remediation," said Darrin Hansen, Wilder's project manager.

Major Commuter Route

The Glenn Highway is a major commuter route, leading to bedroom communities north and east of downtown Anchorage. Putting together a traffic control plan that allowed for both building an interchange and allowing traffic to flow through the area was critical.

"The initial effort started during the proposal phase of the project. We spent a considerable amount of time analyzing the best method of detouring and maintaining traffic to minimize conflicts with the work area," said Hansen.

Wilder worked closely with AKDOTPF in formulating the traffic control plan and work schedule that included up to six weekend closures of the intersection. Wilder used three of the closures to accomplish portions of the project such as removal of the existing pedestrian bridge, erection of the new bridge girders, and installation of a new utility corridor for storm water runoff.

Work zone speed limits were also reduced, and double fines were imposed on those caught ignoring the lower limits. The frequent flashing lights of police cruisers were an indication of a strict enforcement policy.

The simultaneous construction of a junior high school along a portion of the Bragaw Street portion of the project presented an additional consideration for traffic control and access. The school is the replacement of the nearby Clark Junior High School in a project that is spread over two years.

For Wilder, the adjoining project presented both a challenge and a benefit.

"The construction of the new Clark Junior High has presented some challenges primarily isolated to coordination between contractors and access into and out of the work sites," said Hansen. "On the other hand, due to the school construction, student traffic has been removed from the equation, reducing the potential conflicts with increased school traffic by both pedestrians and vehicles accessing the school."

New Bridge

The new bridge that will carry Bragaw Street traffic over the Glenn Highway uses 36-inch inside diameter steel pile for the center pier, concrete spread footings for the abutments, and Bulb Tee concrete girders that were cast in Anchorage. The bridge has two spans. The span over the outbound eastward traffic is 111 feet 2 inches in length. The span over the incoming lanes of the Glenn accommodates a loop on ramp that was unique to Wilder's proposal. That span is 124 feet 8 inches in length.

An arch tunnel under Bragaw Street on the south side of the Glenn Highway will provide pedestrian safety at the newly configured interchange. Wilder used a combination of EFCO Lite wall panels and Redi-Radius arch panels to construct the arched tunnel that is 20 feet wide and 14 feet tall.

"The form system is a combination of smaller modular units that are combined into a larger single 'traveler' form that once assembled allows the crew to cycle the form more efficiently and reduce the time required to complete the work," Hansen said. "A typical cycle involves setting the traveler form to line and grade, installing the reinforcing steel, buttoning up the outside 'gang' forms, pouring concrete, curing the concrete for strength prior to sucking the traveler in and moving it ahead 25 feet and resetting for the next pour," he added.

Surging energy and material costs during the 2008 construction season touched Wilder as it did everyone in the construction industry. The company's response may be typical of the response across the industry.

"As with all of our projects, we do our best to mitigate our exposure to rising raw material costs as much as possible. In some cases, we were able to lock in pricing by buying materials and consumables earlier than planned, while in other cases we did experience increased costs to the project that we could not have reasonably expected," said Hansen.

The project workforce has fluctuated between 15 to 70 people, including subcontractors, averaging 45 people during the 2008 construction season. Work was limited to a single day shift with an occasional night shift added to minimize impacts on rush hour traffic and to expedite construction schedules. Weather, often an issue on construction projects, was not much of a factor for Wilder crews.

The fast-track, design-build nature of the project presented the greatest challenges for Wilder.

"The fact that we started construction prior to having a final design required that the people building the project have a good understanding of the overall plan and schedule and the ultimate goal that they were trying to achieve," said Hansen. That said, he noted the elements essential to any successful project. "Teamwork and communication between all the parties have been a large part of the success of the project," Hansen concluded.

That success will mean one less bottleneck for traffic engineers and, for commuters, one less stop along a very busy route of travel.

Author Information
Gene Storm, an Anchorage freelance writer and photographer, has covered Alaska construction projects for PB&E for nearly 20 years.

         
 

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