A bridge too few is a now familiar cry

The Forth Road Bridge is heavily congested at peak times and rail services across the Forth are also congested during peak periods.

Even if congestion were not a significant problem in its own right, the condition of the existing road bridge has a major detrimental effect on connectivity in the south-east of Scotland.

The most obvious maintenance problem in terms of disruption to transport links is the need to restrict traffic over summer months every four to five years to resurface the main span carriageways. This necessary work results in serious financial damage to those who depend upon a reliable road link, particularly the important tourism industry which looks to recoup the majority of its annual income during the very period that is required for weather sensitive roadworks.

Road surfacing, which lasted 25 years when the bridge first opened, is beginning to fail after only eight years. The material laid in 1998 on the northbound carriageway already needs extensive patching and will have to be replaced in 2007. This premature failure is believed to be as a direct result of the introduction of heavier lorries over the years coupled with the use of the super-single tyre, which concentrates the load on the bridge's steel deck. It is interesting to note that the super-single tyre is not permitted in the US, which has the largest stock of long-span suspension bridges.

The progressive increase in permissible weights of heavy goods vehicles from 22 tons in 1964 when the bridge opened, to 38 tonnes in 1983 and 44 tonnes from 2001, together with the overall increased number of lorries, has resulted in the actual traffic load carried by the bridge being more than double its design load. This has led to overstress in components of the structure, which will require strengthening and possible further restrictions.

Other schemes identified in the 15-year maintenance plan, such as replacement of the main tower expansion joints, bearings and replacement of sub-standard vehicle parapets cannot be delivered without lane closures and inevitable delays to drivers.

In the longer term, it is becoming apparent, through our investigations into the main suspension cable, that a five-year acoustic monitoring programme is required in an attempt to predict its remaining economic service life.

Quite apart from the maintenance challenges faced by the bridge there is the problem of congestion, particularly during peak times when the constraints of the bridge carriageways limit flow. This congestion has been addressed in the recently published Sestran-led Integrated Transport Corridor Studies (SITCoS), which has made recommendations in the short, medium (five to ten years) and long term. The short and medium-term solutions involve demand management together with more rail and public transport improvements. The long-term recommendation includes for the provision of a new multi-modal crossing.

Improvements to cross-Forth rail capacity are already under way and include lengthening station platforms to accommodate longer trains and the progressing of the Stirling-Kincardine rail line. Completion of this line will free up the Forth Bridge from carrying coal trains and permit more passenger services.

Sestran is moving forward with the provision of more park-and-ride sites and the extension to one at Ferrytoll recently opened.

The SITCoS study gave particular weight to investigating the case for and against a new crossing and concluded that by 2011, the "palliative effects" of the short and medium-term recommendations would have been exhausted.

The SITCoS recommendation that no additional lanes for unrestricted traffic be provided on a new crossing is in harmony with FETA's policy. No-one is advocating a replica road bridge. What is being promoted is a multi-modal bridge with lanes for buses, taxis and high-occupancy vehicles on a bridge deck capable of carrying light rail or trams.

Arguments have been put forward for a tunnel rather than a bridge but a tunnel in this particular location has been found, both in economic and engineering terms, not to be viable. Further, there is a detrimental environmental impact associated with tunnels due to the provision of 24-hour lighting and exhaust ventilation equipment.

Without a new crossing there is no opportunity to increase the provision of public transport, travellers will experience increased delays at peak times and even routine maintenance will become more difficult.

Alastair Andrew is general manager and bridgemaster with the Forth Estuary Transport Authority