The Inverness West Link

The Inverness West Link is a £55 million project procured as part of the Inverness and Highland City-Region Deal. The project aims to encourage sustainable regional economic growth, tourism and alleviate traffic congestion. This joint initiative was supported by up to £315 million investment from the UK and Scottish governments, Highland Council, Highlands and Islands Enterprise, the University of the Highlands and Islands.

The Caledonian canal links The Moray Firth at Inverness to Fort William on Loch Linnhe. It passes through five swing bridges and into four lochs Lochs (Lochs Dochfour, Ness, Oich and Lochy) along the route. One of these is the very popular visitor location of Loch Ness. With 1,400 boats each year navigating the canal, the opening of the two swing bridges can cause delays to the traffic around the local area of Inverness.

The first bridge along the canal is located at Muirtown and was constructed in 1935; a second bridge follows at Tomnahurich constructed in 1938. These bridges remained in use with their original electrical control systems until upgrade works were carried out in the 1980s. Around 2010, Scottish Canals identified that access to nearby towns and the sustainability of the canal was to be preserved and that major upgrade works were required.

Fairfield Control Systems was contracted for M+E refurbishments of both bridges. These works extended the life of the bridge, improved reliability. They also provided significant Health and Safety improvements for the operation and maintenance of the bridges and the public who use them regularly. Upgrade works were completed at Muirtown in 2014 and Tomnahurich in 2018.

Tomnahurich Bridge lies on the A82 main road to Fort William. It can cause significant traffic congestion when open to canal navigation. A core element of the Inverness West Link was the addition of a second swing bridge over the Caledonian Canal to the south of the existing Tomnahurich swing bridge.

Phase 2 of the Inverness West Link was completed in June 2021. This included the costruction of a brand-new swing bridge located 200m downstream of the existing Tomnahurich Bridge.

The name of the new swing bridge that spans 37 meters over the canal was put out to a public vote and became known as Torvean Bridge. A new central control tower was located centrally between the Tomnahurich and Torvean bridges providing an operational hub for both swing bridges allowing operators to manage the entire canal and road infrastructure effectively. The intention is that approaching boats are navigated through the first bridge while the second bridge remains open to traffic. Once boats have passed through the first swing bridge, they are briefly held within the central wharf while the bridge is reopened to traffic before boats are allowed to navigate through the second bridge. A vehicle  management system is used to divert traffic over the bridge open to traffic. This enables traffic to continually flow across one bridge whilst also allowing boats to pass through the other before navigating onwards.

The highland council awarded the project to the principal contractor, RJ McLeods who completed the Civil Engineering Works. RJ McLeods subsequently contracted Cleveland Bridge UK and Hedley Hydraulics to provide the Main Bridge deck and hydraulic components. Fairfield Control Systems was contracted directly by The Highland Council to provide the complete electrical installation and bridge control system integration works.

Fairfield Control Systems worked alongside engineering consultants, civil engineers, and mechanical/hydraulic system integrators throughout the design, installation and commissioning process, providing a joint turnkey project solution.

System Overview

The main control system comprises of a new multi cubicle form 4 motor control centre providing power and control of two 22Kw hydraulic slew drive motors and ancillary hydraulic controls; this includes bridge deck tail locating pin, two sets of centre jacks/wedges, and two sets of tail jacks/wedges. Position monitoring of the bridge deck and all hydraulic equipment is provided by dual inductive proximity sensors.

The bridge control system is based upon a Siemens S7-1500 CPU PLC System with local and remote IO, along with a Siemens TP1500 Comfort 15” Touch screen Operator’s HMI and a duplicate HMI located on the local MCC for manual/maintenance operations.

A permanent diesel generator provides a TP+N 400Vac backup supply. In the event of a mains failure a Socomec transfer switch will automatically start the generator and, after confirmation of a healthy supply will change over onto the backup supply. Upon incoming mains restoration, the transfer switch will automatically revert to the mains supply before de-energising the generator. A 24Vdc control ups provide backup during power loss providing power to critical control equipment such as the PLC system.


An operator console is located within the central control tower and provides the primary means of automatic control. The HMI overview displays prompts that the operator must follow to guide them through the opening and closing sequence; these prompts are displayed in the form of text instructions that refresh after each step has been completed. Output control is provided by a series of console-mounted pushbuttons that the operator depresses when instructed too by the HMI prompts. The HMI also provides the operator with critical information, hydraulic equipment status, and any system alarms.

Alongside the operator’s console is a multiscreen/multi-camera CCTV system providing a full 360-degree view of the bridge and the surrounding road infrastructure to monitor the flow of traffic and the position of the bridge.

In the event of equipment failure or a PLC system failure, secondary backup control is provided by a handheld radio-controlled pendant; this coupled with utilising the MCC mounted HMI, the engineer can recover the bridge to a safe condition. The handheld pendant provides the engineer with the ability to control significant items of equipment, including traffic wigwags/barriers, hydraulic pin/jacks/wedges and bridge slew open/close commands.






Bridge control systems incorporate multiple safety functions, including emergency stops, bridge abutment gate access control and safe stop functions.

A safety interlock system utilises a trapped key solution to prevent the operation of the bridges from multiple locations, either remotely at the control tower or locally at the bridge control plant rooms. Manual control of the bridges can be enabled by inserting a safety coded key into the local control panel. Manual control is then provided for maintenance activities or bridge recovery in the event of control system failure. Manual control is carried out by utilising an engineer’s handheld pendant controller. The pendant is provided with pushbuttons for all items of equipment required to operate the bridge.

The Inverness West Link Project provides many benefits to the local areas, including:
• Maintaining traffic flow
• Provided safety improvements to the bridges
• Improved development opportunities locally
• Encourage Tourism throughout the local area

The Torvean Bridge has demonstrated in the short time that it has been in operation the real benefits to users by reducing journey times and easing traffic congestion. Fairfields Control Systems Ltd has played an integral part in the success of this project. Working closely with the Highland Council and other Contractors engaged in the Inverness West Link Stage 2 project. They have overcome many challenges, providing detailed design and site support to the highest standard

Iain MacLennan

Senior Engineer

The Highland Council

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