this brief time, routes were reconfigured to improve reliability in the subway: J Church service operated as an only-surface route between and , requiring transfers to the Market Street subway at Church station. K Ingleside and L Taraval service was interlined as the LK, running between and Balboa Park; no J, K, or L service entered the subway. Light-rail service west of Sunset Boulevard was replaced by buses to allow for construction. Transfers were required at West Portal station. M Ocean View and T Third Street service was interlined as the TM, running between Sunnydale and Balboa Park. S Shuttle service was increased, running with the TM and N in the subway. Advocates with local nonprofit Senior and Disability Action criticized this route configuration, expressing concern over the need to transfer at West Portal and Church stations. In November 2020, the SFMTA that announced some rail lines such as the N Judah and T Third would likely return in early 2021, followed by a gradual return to full operation. Kirschbaum said the agency was reconsidering its approach to maintenance after the botched attempt to reopen in August, and that it might take 5 to 8 years to fully address the system's vulnerabilities. Among the most urgent issues was replacing the track ballast in the Twin Peaks Tunnel, which was meant to be replaced during a maintenance project in 2018 but was instead reused at that time. City supervisors harshly criticized the mistake, which SFMTA director Jeffrey Tumlin blamed on a "culture of fear" he was working to correct since becoming the agency's leader in 2019. The surface-only (from Market Street to Balboa Park) J Church route resumed service on December 19, 2020, followed by the Embarcadero–Sunnydale portion of the T Third Street on January 23, 2021. N Judah and K Ingleside light rail service resumed on May 15, 2021, with the K and T again interlined, along with S Shuttle service now converted to supplementary. At that time, some stations were converted to new wayfinding signage based on international standards, with compass directions like "westbound" replacing older "inbound"/"outbound" directions. M Ocean View light rail service resumed on August 14, 2021. The L remained served by buses due to a multi-year reconstruction on the surface section of the line. Service only ran until 9pm until October 2, 2021, when it was extended to 10pm on Sundays and midnight on other days