Foreign secretary Boris Johnson has raised the idea of building a bridge connecting England and France.
The idea was proposed when he met with French president Emmanuel Macron yesterday.
New Civil Engineer technical editor emeritus Dave Parker said that although the engineering was possible, Brexit could scupper any feasibility.
“We have the technical expertise to build this crossing - but would the politics rule it out? Without freedom of movement for people and freight the crossing would be hard to justify, given how much it would cost.”
Institution of Structural Engineers past president and Cowi director Ian Firth said the idea was “entirely feasible” from an engineering point of view.
“Multiple long span bridges are now reasonably common place and they’re proven,” he said. “The Norwegians are proposing a massive multiple span suspension bridge which has floating foundations for example.”
A bridge across the channel is not a new idea. Firth said that in the 1970s he had worked on a scheme to build a cross-Channel bridge before the tunnel option was chosen. He said the technology available then was less sophisticated than it is today.
“The scheme that was looked at in the 1970s for the Channel crossing was a multiple span suspension bridge,” said Firth. “Back then it was big heavy trusses, double deck and it was a cable stay hybrid.
“It’s come a long way since then and we’re not afraid of multiple spans.”
Firth, a bridge specialist, said there were many examples of bridges, around the world with similar issues to those which would be faced by a Channel crossing either built or under construction.
He said the ground conditions and the depth of the channel would be challenges, but not impossible to deal with.
The English Channel is one of the busiest shipping lanes in the world. To allow for ships to pass through, Firth said the bridge could be built higher in places with a clearance of around 60m to 70m. But he also warned the structure would have to be built to withstand the most severe ship impacts.
He also said the bridge could include sections of tunnel below shipping lanes. In this scenario he said the above ground structure would transition to tunnel via a man-made island.
“The Hong Kong-Zhuhai-Macau bridge in China (pictured) which has just opened, does just that,” he said. “But there are environmental considerations which would have to be taken into account with this.”
He said the crossing, which would be up to 40km long, could be a mix of multi-span sections with concrete approaches and long span lightweight steel sections. Wind shields would be installed on the bridge to ensure traffic is unaffected by stormy weather.
He also said by the time the bridge is built, new technologies such as autonomous vehicles, could help with issues such as vehicle impacts on the bridge. Escape lanes could also be built into the structure to allow drivers to stop if they need to.
It is not the first time Johnson has come up with an unusual idea for crossing the channel, back in 2014 he mooted an extension of the Victoria Line to Dieppe in France.