A balanced design
Tower Bridge
Although its reception in 1894 was far from favourable, the Tower Bridge has become an unmistakable London Landmark and a National Treasure. The bridge, with its majestic stone-faced Gothic Towers was designed to be both elegant and practical.
The bridge is really three bridges in one: the spans from the shores to the towers are suspension bridges, the pedestrian walkways are truss bridges, and the most interesting of all is the centre span, which is a Bascule Bridge. The centre span of the Bridge consists of two balanced, counterweighted sections, known as bascules, that are raised to allow tall ships to pass beneath the Bridge. When the Bridge was first opened, steam engines powered the hydraulic system that raised and lowered the bridge. Today electricity powers the system to raise and lower the bridge. The bridge today rises in 60 seconds and lowers in 75 seconds. The original steam powered system could actually lower the bridge 15 seconds faster than the modern system.
From Walkways to View Ways 
In the original design, the upper walkways that connected the two towers of the bridge allowed pedestrians to travel freely even when the central span was raised, but the walkways soon fell into disuse. Because of this, the walkways were closed from 1910 until 1982, when an act of parliament reopened them. Today, the walkways have been converted to serve as viewpoints for the city skyline.
The Bridge Today
Of the 29 bridges currently spanning the River Thames, the Tower Bridge is the only movable bridge. When the Bridge was first opened, it opened more than 1000 times per year, but today the bridge opens fewer than 100 times per year. Visitors today can see the viewpoints along the upper walkway and tour an original engine room, if they are lucky, they may even be able to catch the bridge being raised for a ship.
Submitted by: A. Wallen, Worcester Polytechnic Institute, 21 January 2007
