Published: Thursday, 15th January, 2009 10:30am

New road bridge plans are flawed

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FORTH replacement crossing plans shown by consultants at a North Queensferry meeting on 8th January perpetuate the design flaw of most UK road crossings by not providing for tidal flow; a desirability recognised there by ex-FETA convener Lawrence Marshall.

Gaining just one lane on the Forth road bridges, to allow 3:2 tidal flow, would help hugely.

Elsewhere, such bridges (eg New Zealand"s Auckland Harbour, USA"s Golden Gate) have uninterrupted decks to allow tidal flow, historically by changeable lane indicators (as on the UK Tamar Bridge, where flow directions may change 15 times per day).

However, a moveable median barrier is now installed on the Auckland Harbour Bridge (moved four times per day), with a one-foot wide version out for tender for the Golden Gate; the barrier gives safety between contra-flowing lanes.

The new Forth road bridge, like the existing one, has fixed constructions between the dual carriageways, so should be re-designed for tidal flow with a moveable median barrier.

On the existing bridge the obstruction is a grill, but at the meeting, plans showed the possibility of replacing the grill with tracks. However, replacing the grill with a road lane and moveable median barrier would safely allow 3:2 tidal flow, obviating the expense of a new bridge.

Leaving the meeting Mr Marshall bemoaned massive transport subsidies by Edinburgh to Fife, specifically "£1 per passenger mile" for rail users.

Fine, chop the subsidies, recognising the Forth rail bridge as untenable for rail, as MSP Helen Eadie did (Press, 6th March 2003), and convert it to road, giving a cheap and quick solution for the Forth crossings.

Michael Arthur,

Transport-Watch.co.uk.