New £4.2bn road bridge over Forth could be a double-decker

THE new £4.2 billion crossing over the Forth could be a double- decker bridge, The Scotsman can reveal.

Buses or trams would travel on a separate deck below other traffic, according to one of three designs from the project team.

Those masterminding the crossing want to create a world-beating structure, with the triple-tower, cable-stayed bridge likely to be among the biggest of its kind anywhere.

However, they admit to facing a unique global challenge – building a 21st-century road bridge beside its 20th-century counterpart and the iconic, 19th-century rail bridge.

Naeem Hussain, the main crossing manager for consultant Jacobs Arup, which is spearheading the work, said it was important the new bridge did not overshadow the others – it must be distinctive, not dominant.

The crossing's three towers will be designed to complement the Forth Bridge's three cantilevers, with the Forth Road Bridge's two towers between them.

Bill Black, a director of Richard Murphy Architects in Edinburgh, was impressed by the preliminary designs. He said: "Both the current bridges are such amazing pieces of engineering, and the new one looks like it will be equally elegant."

Malcolm Fraser, another leading Edinburgh architect, said he was pleased at the "economy" of the designs and that a "gratuitous icon" had not been created. However, he is opposed to a new bridge, as it will increase road use.

The project was approved in December because of fears about the state of the Forth Road Bridge. Corrosion of its main cables from water seepage could force a lorry ban as early as 2013 and closure six years later.

However, the new bridge will not be completed for eight years, and ministers have yet to announce how the structure will be funded and approved.

Alan Seywright, the project director for Jacobs Arup, said the choice of decks would depend on the design of connecting roads at either end of the bridge. The northern landfall in Fife is particularly challenging because of the narrow peninsula and rocky terrain. The precise route of the bridge has still to be decided, but the centre tower will be on the Beamer Rock, midway across the Forth.

Feasibility studies are due to be completed by the summer, with designs being developed early next year and then submitted for approval – probably through an Act of Parliament to be passed in 2010. A competition will be launched to select a builder that year, with construction expected to start in 2011 and be completed by 2016.

The team is also considering restricting the present Forth Road Bridge to vehicles carrying passengers if its corrosion can be halted or the cables replaced.

Many campaigned for a tunnel rather than a bridge, to reduce the impact.

BRIDGE OF SIGHS

RESIDENTS of South Queensferry are far from seduced by the crossing designs and have launched a protest group, fearing construction will ruin their lives.

People living on the western edge of the town said ground investigations had started in a field yards from their houses, without warning.

Alan Doig, of Clufflat, near Port Edgar, said: "This crossing will decimate our families' way of life and severely restrict us financially. This whole project has nothing to do with what is best, it is to do with leaving a legacy and an iconic structure to point at and claim a success."

The Transport Scotland agency, which is in overall charge of the project, said it was committed to "minimise any disruption to communities associated with the new bridge".

A spokesman said: "It is inevitable there will be some disruption, but we will ensure these impacts are mitigated against as much as possible."

OPTION 1

CARS and lorries would use an upper deck while the lower one would be reserved for buses, trams, or possibly other vehicles carrying passengers.

The protractors-style design features tower legs nearly meeting at the top but wide apart at the bottom, joined by a cross member two-thirds of the way up. This option would enable a narrower access road corridor at either end of the bridge.

OPTION 2

A SINGLE deck would carry all vehicles, with buses or trams travelling in dedicated central lanes which pass through the towers.

Other traffic would follow a dual carriageway, with hard shoulder, on the outside of the towers.

In this option, the legs of the three towers would taper to a single point above and below the deck, creating a diamond-shaped space.



OPTION 3

THE deck would be the same as in the second option, with buses or trams running in the central two lanes inside the towers and other traffic on a dual carriageway on either side of them.

However, the three legs would each taper to a single point at the top, but follow a straight line through the deck to form a triangle. Bill Black, of Richard Murphy Architects, favoured this option. He said he liked the "wine bottle" shape.