MARYSVILLE — Replacing critical machinery on the State Route 529 Snohomish River Bridge between Marysville and Everett will close the southbound span this weekend.

From 8 p.m. on Friday, Sept. 27, until 5 a.m. on Monday, Sept. 30, southbound SR 529 will be closed between Interstate 5 and the bridge. The I-5 exit to southbound SR 529 will also be closed. Drivers who need to reach Smith Island can enter SR 529 at State Avenue in Marysville, or follow a detour route on southbound I-5 to northbound SR 529.

During the closure, contractor crews working for the Washington State Department of Transportation will replace heavy pieces of machinery that operate the southbound lift span. The machinery is showing signs of wear and fatigue, including cracking, after 60 years of hoisting and lowering two counterweights weighing a total of 250 tons. The bridge averages about 600 openings each year.

The drawspan machinery is housed in two towers 80 feet above the southbound lanes. The crews from PCL Civil Constructors will use a large crane to remove the old machinery in the southernmost tower and lift the new pieces into place. The machinery in the north tower was replaced Sept. 21-22.

Work on this $3.2 million project will be complete in October.