Build-to-last philosophy is lost

In the mid-18th century, General Wade built hundreds of bridges to help the Hanoverian Army overcome the guerrilla resistance of the Highlanders, writes Christian Wolmar. In the 19th-century, Brunel and Telford and their lesser-known contemporaries built countless viaducts, bridges and arches. Most of these structures, many of which are elegant additions to the landscape, survive today, while their modern counterparts, the ugly squat concrete box girders of the Sixties and Seventies are already falling apart.

Of course, few of the older bridges have to suffer the indignity of carrying an endless stream of 38-ton lorries belching a fiery cocktail of chemicals which, mixed with the salt laid down to de-ice roads, eats away at their structure. Nevertheless, the new bridges fare badly in comparison because the design philosophy is different.

The Victorian arches which carry our railways through towns were over- engineered and built to last forever as the immediate cost did not figure as largely in our forefathers' assessment of projects as they do today. They had to be built very solidly because the Victorians were not so knowledgeable about the loading criteria, and therefore they had to play safe. Nowadays, according to John Whitwell, deputy secretary of the Institution of Civil Engineers, "we would use half the bricks that they did".

We no longer use bricks but modern materials which are not necessarily designed to last. Mr Whitwell said: "Of course, estuary crossings and really big projects are made to survive for 150 years or more, but many bridges are designed to be replaced in 30 years or so."