This is The Lifting Bridge.
It was built between the Ironworks and the Boatdock was built across the railway transhipment basin at Lloyds Proving House near Factory Junction in Tipton. Huge weights near hanging on chains over the four pulleys balance the weight of the roadway, and the deck can be raised and lowered by operating a small hand-winch,
The Lifting Bridge guards the entrance to the museum arm and prevents boats being removed. The flat deck of the bridge makes it easier for vehicles to cross the canal than if a fixed humpback bridge was used.