Seeing as how an underground line from, say, downtown to the Outer Richmond would make too much sense, enter the Central Subway, the city's $1.6 billion project that will run the T-Third light-rail line from Fourth and Brannan streets to Chinatown, with stops at Moscone Center and Union Square. And excavation of almost an entire block in SoMa starts today at Fourth Street between Bryant and Harrison (near the area Whole Foods).

Workers will excavate and estimated space about "500 feet long, 50 feet wide and 40 feet deep" on the busy block, which also hosts a freeway onramp, and then tunneling will begin next year. What does this mean for people on Fourth Street? Well, according to BCN/SFAppeal, "[s]eople living, working or traveling in the area are advised that an increase in noise, dust and truck traffic is expected once the construction starts."

The following changes will occur in the area:

- The 30 Stockton and 45 Union/Stockton began re-routing in January around major construction sites in Union Square and SoMa. These re-routes will continue throughout the duration of Central Subway construction.

- The 8X/8AX/8BX Bayshore Express and 91 Owl will be rerouted in July, and the temporary 8 Shuttle route will be eliminated. Additional information will be available soon online and in media alerts.

- At least two lanes on 4th Street will remain open to traffic while work is in progress.

- Sidewalks on the west side of the block will be impacted.

- Access to Clementina Street between 4th and 5th streets may be restricted at times, but the contractor will facilitate access for deliveries.

- Parking restrictions will be in effect in and around the construction area.

- Electronic messaging boards will be in place and parking control officers and flaggers will monitor and facilitate the flow of traffic as appropriate.

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