In 1877, A Special Bridge or Subway committee was formed to find a way across the Thames, but with the additional problem in that it must not hinder the passage os sailing ships sailing up river. All in all 50 designs were put forward including one from architect Sir Joseph Bazalgette who would later go on and design and build the sewer system which incidentally is still in use to this day. The plans put forward by Horace Jones who was in fact one of the judges, a fact that caused much controversy.
Construction began in 1896 and took 8 years to complete, employing over 430 construction workers through 5 major contractors. 70,000 tons of concrete was sunk into the banks of the Thames so that the 11 million kg of steel for the towers could be supported. The framework was then clad in Cornish granite and Portland stone.
The design itself is a combination of both a suspension and bascule bridge. At each end from the bank to the two towers is the suspension element, but the bascule element is the most interesting.
The above image shows the bascule's of the bridge in motion. The term 'bascule' comes from the French term for balance scale. Each 'leaf' is 31.5m (103.3ft) and weighs over 1 million kg and rises to an angle of 86° and takes 5 minutes to raise from horizontal to vertical. When the bascule's are raised, pedestrians can cross the river by means of the walkway, which at high tide is 44m (144ft) above the river. In 1910 the walkway was actually closed due to lack of use. Today the walkway is fitted with a glass floor and as a result has become a major tourist attraction.
Originally 2 steam engines powered the massive bascule's but in 1942 a third was added to safeguard against any damaged due to bombing. In 1974 the steam engines were replaced with an hydrocholeretic drive system. Visitors can visit the the bridge and original Victorian Engine Rooms as part of the Tower Bridge Exhibition which opened in 1982.
Bus route 78 crosses the bridge daily but on 30th December 1953 the southbound No. 78 was in for a shock. The bridge had been left to a trainee and it is said that the green light was showing, signalling to the bus that it was safe to cross. However as the bus approached at a steady 12mp/h the bascule's began to raise. Albert Gunther the driver had little choice but to continue and jumped the small gap between. Miraculously, just 12 passengers including the conductor were injured but nothing serious and the bus remained upright but had Albert accelerated it would surely have fallen on its side. As a reward for this act Albert was given £10 from London Transport and a further £35 from the City of London plus he received a paid day off!