SAN FRANCISCO (CBS SF) — The much delayed San Francisco Central Subway Project is currently scheduled to finally open for service in the spring of 2022.

The project — which will extend the SF Muni Metro T Third Line through SoMa, Union Square and Chinatown — promises to improve transportation to and from some of the city’s busiest, most densely populated areas.

Originally projected to be finished in 2018, a number of issues have slowed the construction process to a crawl. Below is a list of some past coverage KPIX has done on the long-delayed Central Subway.