SAN FRANCISCO (CBS 5) – Construction of the underground extension of San Francisco Muni’s T-Third line, better known as the Central Subway Project, is set to mark a milestone in the construction phase Tuesday – setting up some notable traffic disruptions.

A major staging area will be established beginning Tuesday at the intersection of 4th and Brannan Streets, causing frequent lane closures along 4th St. The area, known as the launch box, will serve as the entry point for boring machines. Above-ground work will also be visible in the coming months near Union Square and Washington Square, as well as along the Stockton Street corridor. The corresponding traffic disruptions and Muni re-routes are detailed on this map by the San Francisco Municipal Transit Agency.

READ MORE: Scott Peterson Resentenced To Life Without Parole; Laci's Mom: 'You Will Always Be Their Murderer'

When complete in an estimated 7 years, the 1.7 mile Central Subway will connect San Francisco’s South of Market to Chinatown. Central Subway service is expected to launch in early 2019. Union Square will be home to one of the line’s 4 stations.

READ MORE: As SCOTUS Reconsiders Roe, Group Pushes California To Become Abortion Sanctuary

The Union Square station is expected to cost $210 Million, and will link the subway with BART and Muni Metro.

Federal officials gave San Francisco the green light to proceed with major construction work for its $1.6 billion subway expansion project in January.

The project has not come without its share of controversy over supposed design flaws, cost and the necessity of expanding a system that has had funding problems in recent years.

MORE NEWS: Warriors Steph Curry Closes In On 3-Point Record; ' He Changed The Outlook' Of The Game

(Copyright 2012 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)