Deeming a bridge not feasible, the Austin Transit Partnership is moving forward with plans to build a tunnel under the lake. Officials said that those plans are still 15% complete and could change as the planning process progresses.
At its deepest, Lady Bird Lake reaches around 18-feet, according to Texas Parks & Wildlife. To ensure the tunnel is safe, it must be beneath the water, within the bedrock, according to the Austin Transit Partnership plans.
“In the alternate analysis phase we had anticipated that the crossing of the Orange Line over the lake would be a bridge,” said Peter Mullan, Austin Transit Partnership chief of architecture and urban design. “As we got into the preliminary engineering and studying all of the parameters that would affect the alignment of the Orange Line in this location, we realized that there were a number of different potential conflicts with a bridge in this location.”
Because of flood plains at Riverside Drive and Bouldin Creek, as well as busy intersections, the tunnel won’t emerge immediately after the Auditorium Shores stop, which would go underground. In addition, the analysis found that construction of a bridge would require closing 2nd Street to traffic and present utility conflicts from 3rd Street to Lady Bird Lake.
The Austin Transit Partnership offered two possible tunnel exits: the short tunnel would emerge near the intersection of South Congress Avenue and Nellie Street and the long tunnel near South Congress Avenue and Leland Street. The Leland Street exit would mean that the South Congress Station would be underground near Elizabeth Street.
In a comparison of the two options, the Austin Transit Partnership said that the long tunnel offers better access to buses, a better location for the station and less traffic pattern modifications.
However, the analysis also said the long tunnel would be “significantly more expensive due to tunnel length and underground station.” The Austin Transit Partnership board of directors echoed that sentiment when reviewing the network of proposed underground stations.
“We also need to understand anytime we go underground, costs go up exponentially,” said Tony Elkins, Austin Transit Partnership board member.
As for Republic Square, officials said the inability to build under the square due to the Texas State Legislature not passing House Bill 3893 will not be detrimental to the overall downtown design. Instead, the station will shift further north, closer to the heavily trafficked Sixth Street.
“I think that it was really good muscle for us to have to work in a way,” Mullan said. “There are going to be challenges throughout this process, things that come up, we're going to have to figure out how to work around them and solve for them.”