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Thursday, June 03, 2010


This is the 25th of April Bridge in Lisbon. To build it cost $32 million (US $201 million in 2006 prices)(£140 million) & it is 2,277.64 m long. Not bad compared to our proposed £2,300 million new Forth crossing at 2.2km. However the cost of just building it is not the issue I wish to raise. This bridge has not only been subsequently recabled - the alleged reason we need a new bridge is the alleged inability to do this - but with stronger cabling underwent a considerable expansion
From the outset the bridge was designed to carry a road and a lower railway deck and it would have been the longest such bridge had this been implemented at construction. However, it was only in summer 1999 that the lower railway deck was ready for use after major preparatory works which included the fitting of additional cables and the widening of the roadway to six lanes, as well as re-painting of the bridge. The "retro-fit" of the railway track was the largest such project undertaken on a bridge in the world. The rail deck is below the road carriageway and was completed by hauling construction materials up to it, to avoid disruption of road traffic.
Recabling a bridge is obviously a very simple & virtually routine matter compared to building it. In the period since the original bridge the strengths of available materials has increased enormously, indeed we are now able to make carbon nanotubes able to, at least theoretically, construct a space elevator 33,0000 miles long so strengthening such a bridge would be a doddle allowing double decking the present bridge. My suspicion is that they will find it possible to recable shortly after work starts on the new bridge & explain, correctly, that the current bridge is so overloaded that we need both.

The only question then is whether the towers are strong enough to take the extra weight. They are - The suspension cables are the only part of the original structure that has not been enhanced or replaced. The towers and box girders carrying the deck have been massively strengthened over the years. The hanger cables have been renewed as have many of the bolts so it only leaves the suspension cables.

A simple expansion would be to would be to replace the cables & add a fifth lane which, comparing to the Lisbon bridge would cost £10 million at 1996 prices plus inflation.

A fifth carriage would allow for 3 lanes of traffic in the direction of travel at rush hour thereby increasing capacity by 1/3rd at peak times. If cutting a tunnel it will be cheaper & quicker to cut one tunnel at a time & the single completed one can be limited at peak time to traffic in the dominant direction. Matching the full expansion of the Portuguese bridge bridge (5 lanes & 2 railroad/automated light rail/2 extra road lanes) would probably cost a bit more but I can see no way that an expanded current bridge together with a 4 lanes of tunnel (previously est £40 million) totaling 11 lanes of traffic, need cost as much as £100 million.

The attempt to get £2,300 million out of us for this is clearly fraudulent. There may be questions as to who is doing the fraud but as Harry Truman pointed out the buck stops with the government & the Holyrood "numptocracy" MSPs who vote for it. It is far from overstating the case to say that they have a duty to the people they asked to vote for them not to be complicit in defrauding us over over £2 billion. Compared to this their £380 million cost overrun on the Scottish Parliament which has already made Scotland a laughing stock was a minor thing.

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The concept of refurbishing bridges and almost rebuilding them without interrupting traffic is a well known one in the civil engineering world.

Something about this proposed new Forth crossing does not smell right, in particular the amount of money it is forecast to cost.

Why as you say are they not even considering upgrading the present structure.
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