Forth Road Bridge maintenance: EIR release

Information request and response under the Environmental Information (Scotland) Regulations 2004.

FOI reference: FOI/17/02563
Date received: 15 October 2017
Date responded: 28 November 2017

Information requested

Information regarding the following:

1. Why is the FRB restricted to public transport vehicles and cycles?

2.1 Was consideration ever given to allowing HGV's to use the FRB?

2.2 If not, why not?

2.3 If it was, why are they not to be allowed to use it?

2.4 If the reason relates to weaknesses in the FRB does this mean that the strengthening work and anti-corrosion treatment of the cabling carried out on it in recent years has failed in its objective?

3.1 Has any reason been given for environmental factors (eg, climate, salt water corrosion) not being properly factored into the design of the FRB?

3.2 If so, what is it?

3.3 Has the taxpayer been put to the expense of funding these works; or was this funded by insurance?

3.4 Have these (environmental) factors been properly factored into the design and construction of the QC?

4.1 Was consideration ever given to allowing heavy, high-sided vehicles exclusive use of the QC and cars and motor bikes use of the FRB? (You will take my point that this would obviate the problem - as has happened today - of double decker buses not being able to cross the Forth because of high winds.)

4.2 If not, why not?

5. Is it projected that the lengthy traffic tailbacks each way will cease to be a problem once the QC is upgraded to motorway status with a speed limit of 70mph?


As the information you have requested is Environmental Information for the purposes of the Environmental Information (Scotland) Regulations 2004 (EIRs), we are required to deal with your request under those Regulations. We are applying the exemption at section 39(2) of the Freedom of Information (Scotland) Act 2002 (FOISA), so that we do not also have to deal with your request under FOISA. As the exemption is conditional we have applied the 'public interest test'. This means we have, in all the circumstances of this case, considered if the public interest in disclosing the information under FOISA outweighs the public interest in applying the exemption. We have found that, on balance, the public interest lies in favour of upholding the exemption, because there is no public interest in dealing with the same request under two different regimes. This is essentially a technical point and has no material effect on the outcome of your request.

1. In 2005/6, the Forth Road Bridge was found to show signs of deterioration, mainly as a result of the growth and increase in weight of traffic together with the influence of the weather and climate. Following inspection, severe corrosion was discovered and the main suspension cables were estimated to be working with a loss of strength of 8 to 10 per cent.

2.1 and 2.2. Predictions indicated that with the rate of corrosion found and without it being possible to reduce the dead weight on the Forth Road Bridge, it was envisaged that live load restrictions would need to be phased in. The Forth Road Bridge would be required to close to HGVs in 2017 and restrictions on light vehicles could be required by 2021.

An acoustic monitoring system was installed to detect the failure of further strands in the cables and a dehumidification system was installed to arrest the rate of deterioration in an effort to delay the need to introduce vehicle restrictions.

2.3 A number of further engineering challenges were identified with the maintenance of the Forth Road Bridge and together with works expected to be required to carry out the replacement or augmentation of the main cables and the anticipated future growth in traffic, the carriageway restrictions that would be required would be unfeasibly disruptive to the travelling public and businesses, and at significant cost to the economy of Scotland. Despite the measures taken to maintain the Forth Road Bridge and extend its useful lifetime, it was clear that it was not a viable long-term crossing.

Once the decision was made to replace the Forth Road Bridge, the project was progressed on the basis that the Forth Road Bridge would become a public transport corridor.

One of the fundamental aims of the Forth Replacement Crossing Project is to maintain traffic capacity at 2006 levels and not to increase capacity except through public transport improvements.

2.4. Cable inspections in 2006, 2009, 2012 and 2015 found the dehumidification system (2006-7) to have been effective in arresting further cable corrosion. Further wire breaks have been monitored by an acoustic monitoring system (installed in 2006 and upgraded in 2016). Further essential strengthening works will be on-going over the next few years to future proof the Forth Road Bridge as a public transport corridor.

3.1 and 3.2. The Forth Road Bridge was opened to traffic in September 1964 having been designed in accordance with the design requirements at that time. The corrosion protection system on the main cables at their time of construction was as follows:

  • All main cables wires were galvanised
  • Following compaction of the wires, the outer layer was covered in red lead paste
  • Galvanised wrapping wire was then wound around main cable.
  • The outer surface of the wrapping wire was then painted.
  • Finally a protective membrane was wrapped around the cables.

This was the standard corrosion protection system used on suspension bridge cables globally at this time.

3.3. Prior to February 2008, all maintenance works on the Forth Road Bridge were funded via the tolls collected from bridge users. Between February 2008 and the abolition of the Forth Estuary Transport Authority (FETA) on 31 May 2015, the operation and maintenance of the Bridge was funded via a direct grant from the Scottish Government. Since 01 June 2015, the Scottish Ministers, through Transport Scotland, have been responsible for the funding of the Forth Road Bridge.

3.4. Yes. Modern design deals with projects from inception to demolition and involves careful assessment of material types, sources, the ability to recycle, and the reuse and reclaim of materials in line with latest best environmental practice. These conditions are built into Scottish Government/Transport Scotland contracts.

4.1 and 4.2. Despite the measures taken to maintain the Forth Road Bridge and extend its useful lifetime, it was clear that it was not a viable long-term crossing for general traffic. Further, during the Forth Replacement Crossing Project inception and design, objections were raised to prevent all vehicles doing this to encourage modal shift to public transport using the designated public transport corridor.

5. The Queensferry Crossing was designed and built to replace the Forth Road Bridge and not provide any increase in capacity. It is anticipated that when the speed limit is increased to 70 mph once the Crossing becomes part of the M90 that the subsequent increase in the speed limits will allow the Queensferry Crossing to operate at optimum capacity.

As part of a Managed Crossing Strategy all activities will be monitored over the next one, three and five years to inform any future decisions on the usage of both bridges and the associated dedicated public transport link roads.

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