Transbay Downtown Rail Extension — San Francisco, CA
Client
- Transbay Joint Powers Authority
Project Value 
$3.9 Billion
Market
Transportation
Services
Design And Urban Planning, Engineering, Program/Construction Management (PM/CM)
The Transbay Downtown Rail Extension (DTX) will connect Caltrain’s regional rail system and the California High-Speed Rail Authority’s (Authority) statewide system to the Salesforce Transit Center in downtown San Francisco.
This 2.4-mile extension will improve connectivity for commuters and travelers, with work that includes 2x25kV OCS, station infrastructure, U-Wall structures, tunnels, and utility relocations.
We are providing key design services, including the 30% design for the new 2x25kV OCS for the underground extension, progressing toward final electrification. As part of the 4th and King terminal yard reconfiguration, we also designed modifications to Caltrain’s existing OCS system to create space for the main tunnel, while ensuring continuous operations in the active yard. Our scope includes interlockings, electrification of non-electrified yard tracks, modifications to OCS structures, and relocation of Wayside Power Cubicles, with traction power load flow analysis and structural assessments.
Innovative OCS Design For DTX Tunneling
The OCS design for the new extension utilizes components from Caltrain’s electrification project, adapted for tunnel supports. The DTX will be constructed below grade with a combination of cut-and-cover and mined tunneling, creating underground stations and new rail infrastructure.
Long-Term Partnership: Parsons’ Support Since 2004
Serving as the General Engineering Consultant (GEC) since 2004, Parsons has supported every project phase—from conceptual engineering to preliminary design—working closely with stakeholders such as Caltrain, the Authority, and the Federal Railroad Administration (FRA). Our contributions include designing a “Tunnel Stub” concept to minimize disruption and evaluating tunneling methods to reduce risk and project costs.
Full Scope Of Services Provided
Learn more about the full list of rail and transit services provided for this project:
- Project management
- Design criteria
- Rail operations analysis and plan
- Station operations analysis
- Rail, civil, and structural engineering design
- Geotechnical engineering
- Tunnel engineering
- Track alignment and trackwork design
- Cut-and-cover engineering
- Engineering support
- Quality assurance
- Cost estimates
- Fire-life-safety design including fire modeling
- Traction power simulations
- Systems engineering and integration
- Electrical/mechanical/traction power
- Architectural services
- Right-of-way negotiation support, including building protection design
- Risk analyses
Accelerated Progress: Innovation In Transit Development
We continue to support the development of contract packages for enabling works, track systems, and Salesforce Transit Center station fit-out. Despite a compressed schedule, we have consistently met deadlines while introducing innovative solutions that reduce costs, risk, and project duration.
