Designed by the city architects horace jones and and john wolfe barry and completed in 1894 the tower bridge is 265 meters long and took 11,000 tons of steel to build its framework. The tower bridge is the only bridge over the thames river that can be raised as it is a combined bascule ( drawbridge ) and suspension bridge which opens in the middle to allow river traffic to pass through. It takes 61 seconds to open this bridge to the maximum angle of 86 degrees and it opens about 1000 times a year . Today the bascules are still operated by hydraulic power but since 1976 they were driven by oil and electricity rather than steam . The original pumping engines , accumulators , where the energy to open the bridge is stored and boilers are exhibits of tower bridges permanent exhibition .