City looks at plans for a hike and bike bridge

February 06, 2012

By Ann Fowler

Oak Hill bicyclists riding to downtown Austin may get a bridge to help reach their destination if the city and environmentalists can agree to an earth-friendly design.

Annick Beaudet with the city’s Neighborhood Connectivity Division told the Gazette that the need for such a bridge goes back to 1998, when the Texas Department of Transportation turned a northbound shoulder of Mopac into a turn lane for drivers going eastbound on Loop 360. “That essentially removed bike access from the bridge,” she said.

In recent years, the demand for a bicycle-safe route from Southwest Austin to Downtown has grown. “The city’s been trying to remedy that barrier,” said Beaudet. A $7 million grant from state and federal funds will cover 70 percent of the cost of a bicycle/pedestrian bridge, with the remainder to come from local bond funds.

Bicyclists will be able to use the bike lanes on Escarpment to William Cannon, where Beaudet hopes bike lanes will be built from U.S. 290 West to Southwest Parkway. Improved shoulders on Southwest Parkway will provide room for bicyclists, leading to the new bridge, grade separated all the way to Zilker Park and the trail system downtown, she said.

Local resident and bicyclist Tom Thayer calls the project “a fantastic idea.” He believes the proposed bridge will be good for the environment. He said, “Encouraging people to use bicycles and walking is definitely beneficial to the environment. I think this far outweighs the impact construction would have in such a sensitive environmental area. I think a bridge can be designed that has minimal impact on the creek and karst area below. This would be a much smaller impact than any expansion of the highway would have.”

Beaudet emphasizes that the driver of the project is the environment. She said the city has engaged several local environmental groups early on “to assure that the type of structure and how we do it is most environmentally sound and respects the creek in every way.”

Steve Beers of the Save Barton Creek Association told the Gazette, “My friends in the parks, cycling and environmental communities are all in favor of this Mopac bike bridge proposal. Myself, I question it.”

Beers is concerned that the bridge might syphon off funds that could be used for other projects. “I don’t question the functionality of this bridge, just the return for the money,” he said.

Beers said the bridge cannot be attached to the existing bridge. One technique for a freestanding bridge is to pour footings into the karst limestone below.

Local engineer Bruce Melton believes a different method would work better. He said, “There is no way in science that this bike bridge needs to be built any other way than with concrete construction above ground. No drilling into the aquifer needs to happen.”

Melton suggests a gravity (or massive) foundation: “a giant piece of concrete big enough to hold up a bike bridge, placed flat on top of the ground.” He said the city is evaluating the technique, but is fearful it will be rejected due to flood control concerns.

He explained, “One of my engineering specialties is flood modeling. The concerns of the city are erosion around the base of the massive concrete foundation. Standard armoring techniques used for generations can prevent erosion in this case.”

Melton added, “These ‘massive concrete foundations’ are not all that big when it comes to the real world, though. And when they are compared to the designs that the city is considering, they are much less environmentally damaging and will cost approximately the same.”

Beers would prefer a smaller bridge, although he acknowledges it would be more susceptible to flood damage and could be a more challenging ride for cyclists. But it could be less expensive with less disruptive construction.

Ultimately, said Beers, “I am all in favor of a better way for cyclists to cross Barton Creek, if the community wants this design. Some bridge is better than none.” He added, “I think if they do decide to go ahead with a more expensive valley-spanning design, then I hope they use the very most beautiful and graceful design they can, because this bridge would be highly visible to our entire community.”

That’s the plan, according to Beaudet. “It’s going to be amazing,” she says. She envisions the finished bridge being featured on the front cover of “Highway Today” magazine: “It will be the typical spaghetti bowl, but it will be a spaghetti bowl of a different sort – it’s all for bicycles and pedestrians.”