After more than three weeks of delay, the behemoth machine boring the first of two transit tunnels under the Allegheny River is back in operation.

Crews restarted the 500-ton machine this morning, Port Authority officials said. By tomorrow morning, the machine was expected to be about 60 feet below the water surface just off the north shore of the river.

The contractor stopped the machine in mid-April, about 10 feet short of the river, when a large tree trunk, complete with roots, became lodged at the front of the machine. The stump clogged a 10-inch-diameter "slurry pipe" used to move excavated sludge back to a "launch pit" for disposal.

More details in tomorrow's Pittsburgh Post-Gazette.