Transbay Terminal Downtown Extension

The Transbay Terminal/Caltrain Downtown Extension Project (DTX) redevelops an aging multimodal facility in San Francisco. The overall project consists of a new, multimodal Transbay Terminal on the site of the existing Transbay Terminal; a 1.5 mile (2.4 km) extension of the Caltrain commuter rail running from its current terminus at Fourth and Townsend streets to a new underground terminus beneath the new terminal; and a redevelopment area comprising approximately 40 acres surrounding the site.

The DTX will accommodate both conventional commuter rail and the proposed California High Speed Rail, and is projected to open in 2019. It is needed to meet the demands of two of California’s most critical and congested highway systems and to meet accessibility, seismic, space utilization, and safety requirements that are not realized by the current terminal.

As part of the Parsons team, Jacobs Associates is responsible for preliminary design of the tunnel section for the DTX. This will involve multiple, large-diameter tunnels, with a span of up to 62 feet (18.9 m). These tunnels will be constructed by various methods, which may include the New Austrian Tunneling Method (NATM), stacked drift tunneling, or tunnels driven by tunnel boring machines. Geologic conditions vary between sheared, weathered rock and soft soils under the groundwater table, in a seismically active region. The alignment traverses the central business district of San Francisco, which includes mixed use commercial and residential areas, with many buildings of historic significance that require building protection. Following preliminary design, Jacobs Associates will provide final design and engineering services during construction.