As another (albeit long retired) engineer, I have to say that David Bullock’s exposition of the planned A303 tunnel works increases my unease over the latest iteration of this decades-long project. 

He says that the tunnel will be up to 40 metres (131 feet) underground;  but chalk is permeable - who would want to drive (dive?) down that deep and for 2 miles? 

People might even divert on to minor roads to avoid it. 

Frank Conway’s excellent exposé of the additional detail needed raises concerns yet further with regard to the upfront and lifetime costs of fitting out, operating and maintaining the tunnel. 

Tolls in the future? (cf. Blackwall Tunnel.)

 The tunnel seems to be Wiltshire’s HS2:  hideously expensive and unnecessarily complex for its essential function - and it can’t even be shortened part-way through to deal with the inevitable cost overruns. 

Surely it would be possible to “reunite the World Heritage Site landscape” (unseen in living memory) by a six-metre deep cutting, landscaped to minimise noise, at a fraction of the cost and risk, obviating the need for much of the ancillaries that Frank Conway identifies.  

Philip Corp

Devonshire Road, Salisbury

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