San Francisco, California.
The Central Subway is a four-stop Muni Metro extension under construction, expected to open in December 2018. The T Third Street will operate on the Central Subway, and will cease to interline with the K Ingleside.
All stations except for 4th and Brannan Station will be underground. Connections to four BART lines, the Powell-Hyde and Powell-Mason cable cars, the F Market & Wharves heritage streetcar, and all other Muni Metro lines will be available at Union Square/Market Street Station.
Additional information:
https://www.sfmta.com/projects-planning/projects/central-subway-project 