Starting Thursday, only one lane on the Robert Moses Causeway in Islip will be open weekdays from 6 a.m. until 4:30 p.m. due to safety inspections, officials said.

The work is expected to be completed on June 30.

Motorists headed to Robert Moses State Park should expect delays in both directions, the state Department of Transportation said.

The main channel of the Fire Island Inlet will stay open for boaters.

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“This single-lane travel operation is needed to perform bridge safety inspections to help assure the safe operation of the more than 50-year-old Fire Island Inlet Bridge,” the department said Wednesday in a statement.

A speed limit of 20 mph must be observed during the lane closure; transportation workers with flags will signal when motorists can proceed.