For anyone obsessed with the upcoming closure of the Interstate 5 Bridge’s northbound span, set your countdown clock for 212 days.

That’s how long until the span, which opened 103 years ago, shuts down for up to nine days, starting Sept. 12 and ending Sept. 20.

The closure is to replace two trunnions, part of the drawbridge’s lifting mechanism that allows tall vessels to pass under the green structure. The work will replace sheaves, or wheels about 12 feet in diameter, sheave covers, cables and trunnions, which are axles 20 inches in diameter that help lift and lower the bridge.

In 1999, a crack was found in the east trunnion on the northbound bridge’s south tower, just two years after the span was shut down in September 1997 to replace the other two trunnions.

During this year’s work, the northbound span will be closed to vehicles, pedestrians and bicyclists.