Transporter Bridges
Transporter Bridges are possibly the least well known bridge type. Or at least they were until the lads of Auf Wiedersehn Pet decided to dismantle Middlesbrough Transporter Bridge, and ship it off to Arizona. Of course, they did have a little bit of help from the BBC and CGI! The other well known example in the British Isles is the Newport Transporter Bridge in South Wales while a third exists in Warrington
A Moving Bridge
The principle behind a Transporter Bridge is very simple, even if the actual construction and operation is far from simple. Essentially, it is a hybrid between a bridge and a ferry. Whilst it is a fixed link across the river channel, in order to limit the disruption to shipping the bridge deck, or cradle, is reduced to the size of a ferry, and criss-crosses from side to side hanging from cables.
As the diagram above shows (hopefully), the fixed structure can be lifted high enough to allow the tallest ships through, whilst the cradle can be suspended to meet the road level on either side. The cradle cables are attached to a 'trolley' on the cross beam, which runs on a 'railway line' and is hauled back and forth by more cables wound by engines on the river bank. (terminology may not be accurate here).
Why not a fixed bridge?
Transporter Bridges do have some benefits. The cost of erecting a couple of pylons, linking them with a truss and then hanging a cradle from them is cheaper and less intrusive than constructing a road bridge with access ramps that allows the same clearance underneath. Back in the days when cars were rare, and pedestrians could cram into the cradle like sardines it worked well. However, with modern traffic levels, and one car taking up as much room as twenty or thirty pedestrians, the Transporter Bridge is no longer a viable alternative for modern bridge designers.
Transporter Bridges also have benefits over other moving bridges, such as Swing Bridges or Lifting Bridges. The most obvious benefit on a busy shipping area is that the bridge generally has to give way to the boats rather than vice-versa. The final option in such circumstances is a traditional ferry, but on short crossings in busy shipping lanes, a Transporter Bridge almost certainly offered a more reliable service.
See also
- Bascule Bridges - a type of lifting bridge.
- Lifting Bridges
- Swing Bridges
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