What’s a trunnion?

It takes some special parts to keep a 100+-year-old bridge working properly. Some of these parts include trunnions and sheaves. A trunnion is the axle at the top of each tower of the Interstate Bridge that supports the weight of the bridge and counterweights to help raise and lower the lift span. Sheaves are pulley wheels that work with the trunnions.Sheaves for the Interstate Bridge

These types of replacement parts can’t be picked up at your local hardware store. They have to be specially made. Parts for the Interstate Bridge arrived from Alabama last week. The parts will be installed during a nine-day closure in September. (Check out a photo album from the project.)

We often get questions about why the I-5 Interstate Bridge closures are happening this fall. One of the reasons is that a lower river = more “headroom” for ships to fit under the bridge while we replace the bridge lift system.

This means working when the river is at its lowest in September. To keep river traffic moving, they need space to pass under the bridge while we work.

We’ve planned ahead. Now that we’re one month away from the 9-day closure of the NB span (September 12-20), we hope you are planning ahead too. Everyone can help reduce closure-related congestion by delaying or shifting trips, biking, taking transit or working from home.Barge seen from Interstate Bridge

Delays and extra traffic can be expected during our entire work period, beginning this month and through October. Find more details by visiting: interstatebridge.org