Worthy causeway

It seems that yet another vulnerable, wire-stayed bridge is to meet the Forth crossing requirements (your report, 17 March)

This may be questioned in the light of at least one ignored option that fulfils all the crossing needs while generating vital carbon-free electricity. The concept is of a solid, yet "free-flow" causeway or barrage above Rosyth, constructed to carry as many roadways, carriageways, tram and railway lines as necessary. The free-flow aspect arises from numerous submerged tidal turbines along its width producing carbon-free electricity. Apart from periods of slack, the tides never stop and the reversible turbine blades would benefit from both incoming and outgoing tides. The provision of a central bridged gap would allow the passage of ships to Grangemouth.

Ships would pass through unhindered but, when larger vessels required passage, the carriageways spanning the gap could lift or swing. This need not be a too-frequent or lengthy occurrence and times of opening might be pre-planned with Forth Navigation Service to minimise any disruption. Larger ships would be constrained, as at present, to only suitable states of the tide.

Such a structure would endure, be maintenance and weather-friendly and, importantly, with its significant carbon-free energy potential, surely prove to be the real, long-term, dual-purpose solution. We have the technology – it's already being done elsewhere – what an opportunity for decisive and positive action.

TA DAVIDSON

Friarsbrae

Linlithgow

Gavin Scott's comments (Letters, 23 March) in response to mine (Letters, 22 March)

correctly warns about the perceived dangers of carrying hazardous goods through road tunnels and I have no doubt that the various categories of such goods will increase in the years to come.

So far as the Forth is concerned, the solution is simple. Such dangerous loads would use the existing bridge. If the weight loadings are becoming a structural problem, the bridge could be reduced to a single lane in each direction. If the hazardous goods pose such a high risk factor perhaps the question should be why are they on our roads in the first place, passing through areas of dense populations and city centres?

Perhaps Mr Scott is making a good case for all such movements being made by rail.

The second Severn bridge runs virtually east/west with the normal wind direction blowing along it, unlike the Forth crossing, which will be north/south with prevailing winds blowing across the structure.

BRIAN FARISH

Baird Grove

Edinburgh