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The Institution of Civil Engineers Institute / association Website
Last edited 20 Mar 2017

Queensferry crossing



[edit] Introduction

Scotland’s magnificent new road bridge across the Forth estuary, the Queensferry Crossing, is due to open in May 2017. Extraordinarily in an age when big projects are often in the headlines for spiralling costs, it has been procured for around a third of its original budget.

It is the centrepiece of a major upgrade to the important cross-Forth transport corridor in the east of Scotland, representing a total Scottish government investment of £1.35bn.

The new 2.7 km structure will be the longest three-tower, cable-stayed bridge in the world, as well as by far the largest to feature cables which cross mid-span.

The original bridge design approved nine years ago was estimated to cost between £3.2bn and £4.2bn. By extending the life of the adjacent 1964 Forth Road Bridge for light public-transport use and by making clever use of existing road space, however, the cost has been cut by nearly two-thirds.

[edit] Reassessing the old bridge

According to Shackman, "following ministerial announcement at the end of 2007, no future functional use of the existing road bridge was envisaged. But in early 2008, a second investigation gave an improved prognosis for the rate of cable deterioration. This, together with removal of general traffic – which constitutes some 15% of the cable loading – provided hope that a functional use for the existing road bridge might be possible.

"The existing bridge had also been ruled out as unsuitable for future light rail use. However, we felt this finding should be challenged, particularly in relation to perceived problems with rotations at expansion joints. A feasibility study was therefore carried out to evaluate the suitability of the suspension bridge to carry a future light rail system (Hussain et al., 2011).

"This demonstrated that the Forth Road Bridge could provide a public transport corridor, initially for buses, but which could be developed to accommodate light rail or trams if required in the future.

"Additionally, if the Forth Road Bridge was to be retained then it could also continue to accommodate the pedestrian and cyclist facilities. The new bridge could therefore be slimmed down significantly."

[edit] Intelligent transport system

Climie says, "In conjunction with the feasibility study on the existing bridge, it was recognised in view of the high cost estimate that the project should be subject to a thorough value-engineering exercise, making best use of existing infrastructure where possible.

"A total of nine main options were considered to connect the new bridge to the M9 and to M90 motorways either side. All options were assessed in relation to a number of factors including cost, environmental impact, connectivity, traffic routing, design standards – in particular junction spacing – and ground conditions.

"In addition, the use of an intelligent transport system, involving variable mandatory speed limits and variable message signs, was deemed to be a pragmatic way of managing the relatively heavy traffic flows along the project corridor and helping to minimise new road construction. The 22 km long, state-of-the-art intelligent transport system will be the first such application of this technology in Scotland."

This article was originally published as 'Buying Scotland's big new bridge' on 7 Nov 2016 by ICE. It was written by Simon Fullalove.

--The Institution of Civil Engineers

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