Poole Lifting Bridge
Whilst this is also written up as a "Warnings and Dangers" tip (due to the traffic disruption it causes) it is a fascinating piece of machinery.
This is third bridge to be built over this narrow neck of Poole's harbour. The original bridge was a wooden affair, constructed in 1834 as a money-making toll bridge, but because it needed the clearance to allow boats to pass under it was too steeply inclined for most horse and cart traffic. In 1885 this was replaced by an iron swing bridge (once again as a privately-operated toll bridge) until the Borough Council bought it and replaced it with the present lifting bridge which was built in 1927 at local tax payers' expense.
This really is a clever piece of engineering as the road sections on the two halves are counterbalanced so that opening the bridge requires very little effort. The machinery and giant electricly-driven cogwheels only serve to control the lift and lowering as the counterbalance is so fine that despite each section weighing 180 tons the bridge could be lifted by hand.
During the summer the bridge has twelve scheduled lift times, spaced about two hours apart, and depending on harbour traffic can be operational for up to 35 minutes (although the norm is about 15).