Downtown Transit Tunnel

The Downtown Transit Tunnel was a planned light rail tunnel in Downtown Austin, Texas. It was a core feature of the proposed initial investment of Project Connect, the transit expansion plan being undertaken by the Capital Metropolitan Transportation Authority. The transit tunnel would have served the Orange, Blue, and (eventually) Gold light rail lines. The tunnel was eventually cut from Project Connect plans after unexpected cost increases and design challenges.

Route
The tunnel was planned to initially facilitate both the Blue and Orange Lines. The tunnel would run under Guadalupe Street from Cesar Chavez Street to at least 14th Street, as well as under 4th Street from Guadalupe to Trinity Street. In the original full system buildout plans, another tunnel would be dug under Trinity Street from Cesar Chavez Street to 14th Street to serve the Gold Line.

The tunnel was initially anticipated to be 1.6 mi in length. By 2021, planners were considering moving the Orange Line's southern portal to near Lively Middle School at Leland Street, potentially adding a further 2.6 mi in length, citing engineering challenges with emerging close to Lady Bird Lake and the topography of South Congress hill. This extension would have more than doubled the cost of the tunnel from $2 billion to $4.1 billion. Tunnel and surface-level cost increases led to a redesign of the entire planned light rail system in early 2023, with 5 options presented to the public for feedback in March. Only one of those options included a tunneled segment, which would have run 0.9 miles (1.4km) under Guadalupe Street from 8th Street to 20th Street and included one underground station at 15th Street. This plan was not selected, and the first phase of Austin's light rail network will not include any tunneled segments.

Stations
The initial proposal planned multiple underground stations for the light rail lines, at locations including Republic Square, Downtown Station, Government Center, Auditorium Shores, Congress Avenue, and Rainey/MACC.

The underground stations would have varied in size, with Republic Square and Downtown Stations being the largest, and all other stations being smaller. Large stations such as Republic Square were initially designed to have three levels. The shallowest would have contained a food court, a mezzanine with a performance stage for local music, and pedestrian tunnels to provide access to other buildings in Downtown. A middle level would have contained small shops and restaurants, public restrooms, and seating, and the deepest level the platform for boarding trains. Underground stations were planned to be fully climate-controlled, utilizing technologies such as platform screen doors to assist with climate control and enhance passenger safety.

By 2022, cost increases meant that many proposed features of the underground stations were removed from planning. All initial and additional underground station proposals were removed from the project in March 2023, being replaced with the lone 15th Street station, which was itself removed in May.