AT the start of this month Transport Scotland was given the go-ahead to demolish part of the Kincardine Bridge. The southern viaduct is to be pulled down and replaced over the next two years. A temporary bridge will be built alongside the existing structure to ensure traffic keeps moving, while timber jetties will be refurbished, navigation lights will be installed and the bridge drainage system will be replaced.

In short, the bridge, which, truth be told, has always looked more characterful than handsome, is getting a facelift. Quite the 85th birthday present.

When the bridge was awarded Category A status by Historic Environment Scotland in 2005, it was in recognition of the bridge as a feat of engineering and a reminder of Scotland’s pre-eminence in that field.

The bridge, 822 metres (2,697ft) long and designed by engineer James Guthrie Brown of Sir Alexander Gibb & Partners, opened on October 29, 1936, the first road crossing of the River Forth downstream from Stirling. To accommodate river traffic travelling to the port of Alloa, it had a central swing section 111m (364ft) long which could turn 90 degrees around a central support.

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As such, the bridge was not only the longest road bridge in Britain at the time. It was also the largest swing span in Europe. The central structure that weighed 1,600 tonnes could be moved using just “three farthing’s worth of electricity” (less than a penny in today’s money) to leave a clear passage of 46m (150ft) for ships.

A photoelectric cell was used to control the exact degree of the swing, the first time this new technology had been used in such a way.

As the years pass such engineering achievements start to become overlooked, taken for granted. We don’t even notice them unless we’re stuck in a traffic jam. Perhaps that is how it should be. Engineering doesn’t have to show off. It just has to work. And the Kincardine Bridge does.

Times and needs change, of course. As river traffic declined, the need for the swing section of the bridge disappeared. It last opened in 1987, and was locked in 1989, the same year the port of Alloa closed. In 2008 the nearby Clackmannanshire Bridge opened and was soon carrying 14,000 vehicles per day.

But even now the Kincardine Bridge remains in use, a concrete and steel pin that connects both sides of the River Forth, drawing them together in the way only engineering can.