How deep are the single-bore tunnel station platforms?

At approximately 90 feet below ground, the boarding station platforms are comparable to other underground stations in California and around the United States. Within the Bay Area, it is about the same depth as the soon to be opened SFMTA Union Square/Market Street and Chinatown Central Subway Stations. Washington Metro, which is the second busiest heavy rail system in the United States, has multiple stations that are even deeper, including ones that are over 100 feet deep.