SAN FRANCISCO (CBS SF/AP) — Crews plan to start digging up a square block of San Francisco Tuesday for a new subway tunnel to Chinatown, even though funding remains up in the air.

The contractor plans to begin building the launch point on Fourth Street for two tunnel boring machines that will begin work next year on twin tunnels for the 1.6-mile Central Subway line.

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Some preliminary work began last week.

The work is going to create headaches for many commuters as there are already two of four lanes closed between Harrison and Bryant on Fourth Street under Interstate 80.

Harrison Street, which is a busy corridor that many people use to get to the Fourth Street on ramp, is already coned off, with drivers squeezing into one left turn lane and one freeway lane.

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The lane closures make it especially difficult for larger vehicles to maneuver in the area as many truck drivers said there is very little space to squeeze by.

KCBS’ Holly Quan Reports:

Authorities anticipate they’ll get $942 million in federal funding for the project—the bulk of the $1.6 billion cost. Congressional approval is expected this fall.

Critics, however, argue that the project is too costly and would be underused. They’re campaigning to kill the federal funding.

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