Two of Muni’s most heavily used bus lines will be rerouted near Union Square due to construction work for the agency’s Central Subway project.

The 30-Stockton and the 45-Union, which collectively carry nearly 35,000 passengers each day, both travel down the Stockton Street corridor that is most affected by the Central Subway work.

As a result, downtown buses on those lines will be rerouted off Stockton Street to Sutter Street and then south on Mason Street. Once those buses hit Market Street, they’ll travel east to Fifth Street, where they’ll resume their southbound routes. Buses travelling in the other direction — from the Financial District to Chinatown — will not be rerouted.

Along with those reroutes, Muni will be adding a shuttle for the 8X-Bayshore bus, which also travels down Stockton Street. The shuttle will provide supplemental service for the 8X.

The scheduling changes will start on Jan. 21.

Construction in Union Square for the $1.6 billion Central Subway, which will connect Muni Metro passengers from Chinatown to the SoMa District, is expected to last another four years.

wreisman@sfexaminer.com