Years of planning, negotiation and problem solving will culminate Tuesday in a groundbreaking ceremony to mark the beginning of construction this fall of the Mockingbird Pedestrian Bridge at Katy Trail.
“This is kind of the big critical piece that connects the existing Katy Trail,” said Jared White, a Dallas transportation planner. “This is how we can get across Mockingbird and get everybody out to the northeast Dallas White Rock Lake area.”
The $7 million construction project is the last phase of the popular Katy Trail, which now runs 3.5 miles from American Airlines Center downtown to near the Palomar Hotel just south of DART’s Mockingbird Station.
By late 2015, a cantilever suspension bridge, supported by three 80-foot-tall towers, should cradle a 14-foot-wide trail across Mockingbird Lane traffic as a kind of mini-Margaret Hunt Hill Bridge.
The suspension bridge’s aesthetic appeal has value itself, said Michael Hellmann, manager of planning and acquisitions for the Dallas Park and Recreation Department.
“The design of the bridge is very important as it goes over a pretty high-profile roadway,” Hellmann said. “It helps put a face on our trail network that people will now see it. Most of our trails are hidden on the greenbelts or on the railroad corridors. It now interacts with the public streets.”
The bridge is something of a 21st-century Promontory Summit for Dallas’ trail system. When completed, the Katy Trail will link at White Rock Lake with trails south to Deep Ellum and north to Richardson and beyond.
“We have a very significant kind of loop forming here,” White said. “If this bridge wasn’t there, it would be a lot more difficult, and we wouldn’t have as seamless a connection getting from one part of the city to another.”
The bridge will make Mockingbird Station more accessible to both bicycle commuters and pedestrians who live in the area and others who will be able to enter the trail network by traveling to the station.
Hellmann expects the bridge to relieve congestion on the Katy Trail by spreading users out over more of the network.
Dallas City Council member Angela Hunt is among the bridge’s longtime supporters.
“It’s wonderful. It’s terrific to see that we are finally moving forward,” Hunt said. “I do wish that we’d been able to accomplish this a little more quickly, but I’m very pleased that we’ve got some momentum behind us.”
Although Hunt is perhaps the person most identified with the bridge, she said the idea was that of former council member Gary Griffith.
“I give a tremendous amount of credit to Gary Griffith for getting the ball rolling,” Hunt said.
The bridge is the last segment of the Katy Trail to be built, because of its location in the highly developed, heavily traveled area near the DART tunnel from downtown. Agreements had to be made with DART, many property owners and holders of utility rights of way.
“This one is kind of unique because we’ve never done this kind of bridge before,” said Chiamin Korngiebel, project manager for Dallas. “It’s kind of interesting and a lot of challenge. It’s very different than what we originally planned.”
Initially, it appeared to be a relatively easy project: sink a few standard concrete abutments to support a prefabricated bridge.
But the bridge designers, HNTB Corp., had to work within the confines of the built-up area without putting weight stress on the DART tunnel below or endangering anchors for related retaining walls.
“We purposely took this piece out of the overall design schedule in about May 2006,” Korngiebel said. “That’s why — officially — this piece became Katy Trail VI.”
Planners tried several ideas, none of which would satisfy DART’s requirements. They decided to use micropiles, groups of small cement-filled steel tubes for the tower foundations. The micropiles can be installed with lighter, less disruptive construction equipment and weigh less than a standard-size abutment.
But even micropile technology wouldn’t work, given the location’s numerous restraints.
HNTB tunnel specialists in New York and Boston suggested moving the micropile foundations away from the sensitive areas and using cantilevered beams for support.
But other problems remained. Trail approaches needed to be constructed to each end of the bridge without putting much additional weight on the sensitive areas. Normally, the trail approaches would require 10 to 16 feet of fill dirt to bring them up to bridge level.
The designers used ultralight expanded polystyrene blocks — similar to those used for Klyde Warren Park — to reduce the weight that would be gained by the equivalent of using one foot of soil fill.
The Katy Trail Phase VI is about 0.7 miles long and includes a second bridge over the DART Red Line. The total cost to design and build the project is estimated at $12 million.
“This entire project — all the way from American Airlines Center out to White Rock Lake — was funded with transportation funding,” White said. “It’s part of an old air quality program for projects that would help reduce the region’s air-quality problems. That’s how the majority of it was funded.”
AT A GLANCE: The ceremony
What: Mockingbird Pedestrian Bridge groundbreaking
When: 10 a.m.
Where: Residences at Hotel Palomar, 5656 N. Central Expressway
Via Dallas News