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PHX Finalizing Sky Train

Rendering of the new PHX Sky Train at Phoenix Sky Harbor International Airport
Final testing is under way for the new PHX Sky Train at Phoenix Sky Harbor International Airport. © Bob Perzel

A new automated people mover will carry about 2.5 million riders per year to the nation’s ninth-busiest airport, easing curb congestion.

January 29, 2013 —Phoenix Sky Harbor International Airport is in the final testing stages of the PHX Sky Train, an automated people mover (APM) system that will eventually shuttle passengers along a 1.7 mi route that begins at an intermodal ground transportation center at 44th Street and ends at Terminal 4, the airport’s busiest terminal.

The tight site at the nation’s ninth-busiest airport and the difficult soils weren’t the only challenges that engineers faced in designing and building the PHX Sky Train. By far the best route for the guideway required a 340 ft bridge to span the airport’s busy Taxiway Romeo, designed for large Class V aircraft with wingspans of more than 200 ft.

“The biggest challenge was it’s never really been done over an active taxiway,” says Mark Pilwallis, P.E., S.E., a senior project manager for Gannett Fleming, Inc., in Phoenix. “So we had to work a lot with the FAA [Federal Aviation Administration] just to develop criteria that they would find acceptable.” 

 Rendering of the sleek 44th Street Station linking to an intermodal center

The sleek 44th Street Station links to an intermodal center.
© Bob Perzel

Although engineers first considered going under the taxiway, that option actually had several serious disadvantages. A complex underground environment of utilities meant that the underground option wouldn’t be less costly. Additionally, the elevated APM system had to connect to Terminal 4 at level 3 to provide the airport with the most efficient operation.

“We were really limited in where we could put the Terminal 4 station,” Pilwallis says. “We wanted [the station] to be elevated … so we can easily [bring] the passengers right into the passenger level. If we went under Taxiway Romeo, we couldn’t get up high enough to get to where we wanted the Terminal 4 station. But if we went over Romeo, the geometry of the profile coming into the station was pretty nice. So that drove the decision. “

The team was initially concerned about reaction from the FAA but found it to be supportive. Team members were instructed to develop and present detailed design criteria, which were ultimately approved by FAA technical reviewers. A minimum bridge vertical clearance height of 75 ft was determined to allow adequate tail clearance for a Class V aircraft with a nose landing-gear failure.

The approval process for the bridge was approximately six months and included consultations with control tower personnel and airline representatives. The project was delivered through a construction manager at risk method, the construction manager was brought on board after roughly 30 percent of the design was complete. That proved to be a great benefit to the project.

 Rendering of the guideway connecting to Terminal 4 on the third level

The guideway connects to Terminal 4 on the third level, bringing
riders into the airport on the passenger level. © Gannett Fleming,

Early plans called for a segmental concrete bridge over the taxiway to minimize the closure to a maximum of two months. The contractor suggested that a cast-in-place bridge, while expanding the taxiway closure to six months, would also save $1 million. Airport officials accepted a six-month closure during the slower summer season for a cost savings of $1 million.

“Once we got past all the approvals, the biggest challenge of the bridge design was creating something that could be built in a really tight environment,” Pilwallis says. “Most airports aren’t laid out with the thought of putting a transit system through it later. And it’s fairly congested as you come through there.”

Moving from a precast segmental bridge to cast-in-place concrete spared the team the cost and logistical challenges of transporting large precast segments to the site and developing a large staging area for the segments.

The taxiway bridge is composed of a 340 ft main span and two 200 ft end spans. The massive cast-in-place box girders vary in depth from 8 ft 9 in. to 17 ft 6 in. The girders have an 8 in. top slab, 12 in. thick webs, and a bottom slab from 12 in to 24 in. The team used 5,900 cu yd of concrete and 1.2 million lb of uncoated, non-prestressed reinforcement.

The tight site and sand gravel cobble soils presented a challenge for the team. The foundations utilize deep drilled shafts from 6 ft in diameter to 10 ft in diameter. Massive augers were deployed in tight conditions to manage the massive 3ft to 4ft diameter boulders the team encountered during foundation work. (See the feature “On Solid Footing,” Civil Engineering magazine, May 2011.)

“In and around the Terminal 4 station, obviously a lot of the work was done at night,” Pilwallis says. “You start mobilizing about 10 PM or 11 PM, and then you really get to work from about midnight to about 4 AM. Then you have to start clearing the site again. Juggling the crews and working in really short windows of opportunity was the real challenge.”

The team used building information modeling (BIM) for all disciplines and shared those models with the contractor. Pilwallis says the team became convinced that BIM was a necessity.

“It was really helpful in resolving the conflicts between the disciplines,” Pilwallis says. “And also understanding what room was left for the train supplier when they came along to put their gear onto the facilities that we designed.”

 Interior view of Terminal 4, displaying art glass walls

Art glass walls were installed to satisfy a Phoenix statute
requiring that one percent of the cost of all capital projects be set
aside for public art installations. © Bob Perzel

Bombardier Transportation USA, Inc., of Pittsburgh, was selected as the system supplier. The APM utilizes two- and three-car, driverless, rubber tired Innovia APM 200 vehicles that operate on concrete plinths cast onto the guideways. A center rail guides the vehicles and provides the power and communication connections. The vehicles can be expanded to four cars as the airport grows.

“The thought was, if we are going to make this investment, let’s make it expandable so it really lasts for the long term, but not build it out to its entirety on day one,” Pilwallis says. “The system will be able to grow and expand to accommodate the airport’s ground transportation needs for the foreseeable future.”

The project includes several art installations thanks to a City of Phoenix measure that requires that one percent of capital project budgets be reserved for public art installations. The stations feature art terrazzo floors, a custom ceiling, and art glass walls.

“Seeing them in place, it turned out to be a wonderful idea,” Pilwallis says.

The APM is the product of a comprehensive landside ground transportation study that Gannett Fleming, Inc., conducted for the airport in 2005. Traffic congestion was an issue, competition for curb space was intense, and roadway expansion wasn’t an option.

With the opening of the Sky Train first stage likely in the first quarter of this year, the airport is already building a 3,000 ft extension to Terminal 3. That extension will include a walkway to Terminal 2, effectively linking all terminals to the Sky Train. The extension is scheduled for completion in 2015. Approximately 2.5 million passengers are expected to ride the train the first year.

A final leg, in the planning stages, would connect the system to the rental car center.



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