In this view of Shelburn you can see both the upper and lower swing bridges across the Gorge of Eternal Peril. The lower bridge provides access to West Salem and sports a sign warning not to attempt a duckunder while the bridge is closed. With a bottom elevation of less than 36" you'd need to be professional limbo dance to do this and I'd hate for you to come up too soon and damage the bridge (or yourself). Permission from the dispatcher is required to open the lower bridge during an op session and the upper bridge remains closed while a session is in progress.

Look at the trackplan.