Connections are key

The airport's goal is to connect each passenger to his or her next flight in 30 minutes or less, which meant the current people-mover system had to be replaced.

"It's virtually impossible to connect passengers through the existing system or across the road by busing," said Clay Paslay, executive vice president for airport development at DFW. "What drove us to the final decision was the growth of American [Airlines] into multiple terminals."

With the construction of Terminal D, American Airlines will be in four terminals, making it even more difficult for passengers to meet their connecting flights without a better system in place. In addition, DFW is one of only two airports in the country serving as a hub for more than one carrier.

Obviously, the replacement system had to be constructed with minimal impact to airport operations. The airport considered several options, from underground trains to a system that would run on the roadside or roofs of the terminals, Paslay said.

Going underground would be astronomically expensive, and a roadside system would have required the fronts of terminals to be blocked during construction, Paslay said.

In the end, a fully automated, elevated APM that runs on the airfield side of the terminal was chosen.

Setting the stage

The airport determined that the best way to get the APM constructed, without disrupting flights, was to construct it at the roofline on the airfield side. But that strategy required a huge commitment from the airlines, said Andy Bell, SkyLink managing executive.

"American Airlines even set aside two people whose full-time job is to coordinate with our daytime and nighttime operations," said Perfecto Solis, DFW Airport's assistant vice president for program development. "On the flip side, we gained a thorough appreciation of airline operations. It was a great education both ways."

Because of the immense size of the 12,000-plus construction crew, as well as the proximity of the project to workers unfamiliar with the construction process, the airport went out of its way to put extra safety measures in place.

"To the flight crews, what we are doing looks intimidating," Bell said. "So we didn't just go by OSHA standards, but went further with higher fences and extra safety people."

The airport also established a 40-hour, bilingual safety training program for the Capital Development Program's construction personnel. As a result, the incident rate for the program is one of the lowest in the nation at .46 percent, compared to the national average of 4.1 percent, Paslay said.

To make room for the APM and give construction crews a right-of-way, most jet bridges had to be extended further from the terminal. More than 4,000 ft. were added to existing bridges at 68 of the airport's 113 gates, and several fueling stations were moved.

The construction team also had to drill and build on the airfield's 30-year-old foundation, which covers a web of fuel, electrical and water lines. "We invested in leading-edge equipment for testing," Bell said. "And we had no major hits. We missed all fuel lines and had no electrical disruptions. As long as we remain invisible, everyone is happy."

Taking the red-eye approach

When work began on the airfield side of the terminal, most construction had to take place at night to avoid disrupting airline operations. Specific gates were scheduled to close each night at about 9 p.m.

The airlines had to move planes, baggage-handling equipment and other items away from the construction area. Then, construction crews moved in, completed a task and had to be clear of the area by 6 a.m.

"Nighttime closures impacted about 70 percent of all gates," Bell said. "As of today, we've had 30,000 individual gate closures."

At the peak of construction, up to 25 gates could be closed on any given night, Solis said. "At 9 o'clock at night, it looked like an airport. But by 10:30, it looked like a ship- building yard," he added.

At around 4 a.m. or 5 a.m., work would stop and crews would begin cleaning up. In most cases, every trace of ongoing construction had to be removed from the area by 6 a.m.

"Every night, there was a virtual army of contractors and materials just waiting for the predetermined hour too start work," Paslay said. "When work could begin, it was like ants pouring out of an ant hill. Then, like Cinderella, the clock would strike and they had to get out of there."

Column construction goes mobile

The new guideway looks similar to a highway overpass that goes in a continuous circle around the airport. It is held up by 370 columns, which range in height from 50 to 70 ft. The typical column shape is oval and averages eight ft. by six ft. in depth.

Usually, such structures would be cast in place. But for those columns, which rise above the airfield, casting in place would have required long gate closures, which was not an option. The columns on the airfield had to be pre-cast in another location and then erected onsite. While 118 columns were cast in place, 252 had to be pre-cast. Of those, 1,008 segments were fabricated offsite. Approximately 2,000 tons of reinforcing steel and 13,000 cu. yds. of concrete were used in the pre-cast segments.

Each column sits on an 8-ft.-drilled shaft that ranges in depth from 30 to 80 ft. undergound. The four column segments and a pre-cast bent were held together by tension rods during erection. After all the components were erected, post tension cables were looped through the whole column assembly and the base support and stressed.

The columns are connected by the guideway on which the APM will travel. The guideway features a built-in heating system with warm-water-and-glycol filled tubing to keep the track clear of frozen precipitation. When the temperature reaches 37 degrees and the air hits 60 percent humidity, the solution flows through the system to prevent the accumulation of snow or ice.

Going up

The guideway connects the airport's existing and future terminals, which will include two SkyLink stations each that will run approximately 480 ft. long. The stations come equipped with synchronized doors, passenger information systems, escalators, stairs and elevators. The stations, which are currently built and awaiting some finish-out, will eventually have trains pull in on both sides.

When the design concepts for the stations were originally presented, engineers determined that 48 columns would be needed to support each structure. But this disrupted the minimalist, clean design that project designers wanted.

Instead, 10 large "hero" columns were erected in each station. These 8 ft. by 10 ft. columns were pre-cast in two segments. They were hollow in the middle to reduce weight and facilitate both transportation from the pre-cast yard and placement by crane. Once set in place, numerous post-tensioning tendons were routed through the two column segments and the supporting base. Those columns were organized in pairs and a large, steel, double-plate bent was placed on each column pair. The result is main station bents that support the bulk of the building loads and all of the train and guideway loads.

The stations' interiors are set off by minimalist spotlights. During daytime hours, most lighting is provided by natural sunlight streaming through a bank of towering windows on either side, from which passengers will have commanding views of the airport and downtown Dallas. Each station also will sport terrazzo tile flooring.

The guideway also leads to a 100,000-sq.-ft. maintenance and control facility.

All aboard

Once the stations and guideway are complete, the project will be turned over to Bombardier, the vendor chosen to provide the APM train system. The system should be ready for public use in the first quarter of 2005, with testing scheduled to begin as early as this month.

The airport has purchased an initial fleet of 64 silicon-coated fiberglass cars, each about the size of a city bus, which are suspended on rubber tires. They will travel in pairs at speeds of up to 35 mph.

Twenty-four two-car trains will be fully operational at the outset and will be able to transport 5,000 passengers per hour, per direction, for a total of 10,000 passengers per hour. Ultimately, more cars can be added to transport a total of 8,500 passengers per hour, per direction, for a total of 17,000 passengers per hour.

Talking it over

The size and scope of the project required Paslay and his team to perform detailed planning years before construction began. Before launching any phase of the Capital Development Program, the airport constructed an onsite facility where all decision-makers could log on to the same computer network. "Collaboration is vital," Bell said.
"We are dealing with a huge mixture of multiple companies and egos." And when challenges arose, they had to be resolved quickly.

"We resolve conflicts as we go," Solis said. "We get everyone in a room and say that nobody is leaving until this is resolved."