Forth Road Bridge Dehumidification

Our works at the Forth Road Bridge were the first works of this type that we were commissioned to undertake. Using our bespoke ‘cable crawler’ access gantry, we installed a dehumidification system to the main cables to inject dry air into the cable at a number of locations. This reduces the speed of corrosion and extends the life of the cables.

Key Project Details

Client Fourth Estuary Transport Authority
Duration 134 weeks
Location Edinburgh

Project Scope

A key part of the process is the subsequent sealing of the cables with a proprietary material to create an air-tight environment.

The project scope includes;

• Unique ‘cable crawler’ access gantry design
• Installation of dehumidification system
• Testing and commissioning
• Significant work at height

The project involved

Significant work at height
Installation of dehumidification system


Our approach to works of this type requires only a single carriageway possession for installation of our bespoke ‘cable crawler’ gantry. Once the gantry has been manoeuvred from the delivery vehicle to the landing trestles, the carriageway can be re-opened with only a lane-one closure required.

Our in-house development of the ‘cable crawler’ gantry for suspension bridge main cables has not only had significant positive contributions to project programme, quality and methodology, it has also created opportunities to carry out other essential works without the requirement for carriageway possessions on heavily used and critical transport routes. Any other methodology would require full-time lane closures, carriageway possessions, multiple crane lifts and significant disruption.

Find out more about our Bridges services

The project involved

Unique 'Cable Crawler' access gantry design