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Figure 30 comprises two pictures of suspension bridges spanning the Avon Gorge. The first picture is a photograph of the actual bridge designed by Brunel and the second picture is a drawing of the Telford design. Both bridges support a level road from the top of the gorge on one side to the top of the gorge the other side. The road is 75 meters above the high water level of the tidal river Avon. At this point the gorge is about 200 metres wide. Both designs use a central span supported between two towers. In the Brunel design the towers are on the top of the gorge at either side and the span between them is 214 metres. The towers look like they are built from brick and stone and are 26 metres high. The top of the towers support the suspension cables. The towers are slightly thinner at the top but have to be wider at the bottom to accommodate the road passing through them. In the Telford design, the towers are closer together and are built on the banks of the river in the bottom of the gorge. They therefore have to rise 75 metres to reach the required level for the road and then rise further to provide the necessary support height for the suspension cables. The span between these towers is much less than the Brunel design being only as wide as the river at this point. Again the towers are designed in brick and stone. They are also wider at their base, not to accommodate a road but to provide a stable support for the much taller tower. These towers have three sections. Two sections are below the road and the third is above the road providing the support for the suspension cables. The widest section is at the bottom, the second section is thinner and the third section is thinner still. In the Telford design the road passes through the base of the top section and so if the road were the same width as the Brunel design then the scale of the drawing indicates that the bottom section would be 3 to 4 times wider than the Brunel tower.

 2.6.1 Innovation