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Paisley Canal electrification

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With 235 route miles, Glasgow boasts the UK’s largest electrified network outside London. Since the introduction of the Blue Trains on the 50 miles of the north Clyde electrics route in 1960, it has progressively expanded with the latest addition, the Airdrie to Bathgate line adding a further 32 miles to extend it to Edinburgh in 2010.

Most of the network on the south side of the Clyde is electrified, although the Paisley Canal line is not. However, this is now the subject of a unique low-cost scheme which will add a further five electrified route miles by December.

Canal heritage

As may be imagined, when the Paisley Canal route started life, traffic was carried by boat. The Glasgow, Paisley and Johnstone Canal was designed by Thomas Telford and operated from 1810 to 1881, when the Glasgow and South Western Railway Company closed it to build a railway on the route.

With its canal heritage, the line has the world’s oldest railway bridge in active use – the former canal aqueduct over the river Cart which was also the longest aqueduct arch of the canal age. A more sombre record is that Paisley Canal station was the site of the UK’s worst canal boat disaster in 1810 which cost the lives of 84 people after a craft carrying day trippers overturned.

The Paisley Canal line from Glasgow to Elderslie on the current Glasgow to Ayr line opened in 1885. This line was closed to passenger traffic in 1983, although a section between Glasgow and the fuel depot at Hawkhead was kept open for freight traffic. In 1990, a Strathclyde Passenger Transport initiative resulted in the resumption of passenger services between Glasgow Central and a new Paisley Canal station with five intermediate stations.

The case for electrification

This service is currently run by three dedicated class 156 DMUs. These could be better used elsewhere in Scotland and the service could be more efficiently covered by better diagramming of the class 314 and 380 EMU fleets.

Moreover, DMUs are hard pressed to meet the timetable due to single line constraints which would be less of an issue for EMUs with their greater acceleration. Thus, for both ScotRail and Network Rail, there is a strong business case for electrification of the line, especially as one third of the route, the first three miles to Corkerhill Depot, is already electrified and no additional HV switchgear is needed.

However, an initial study identified that, for a conventional electrification scheme, nine of the twelve overbridges on the line would require electrification clearance work. This included three bridges adjacent to stations where any track lowering would also require platform re-construction. As a result, the cost of a conventional scheme was estimated at between £20 and £28 million, about twice that which could be justified. If the canal line was to be electrified, an innovative approach would be required.

An alliance that delivers

Network Rail’s policy of devolution and closer working relationships with train operators has borne fruit in Scotland in the form of a new alliance with ScotRail, one of the first train operating companies to sign up to such an arrangement. A tangible result is the way the two partners worked closely to dramatically reduce the cost of Paisley Canal electrification. This included discussions to determine the required six week construction period and associated disruptive possessions which would ensure that the work was completed for the December timetable change.

For its part, ScotRail waived its right for compensation payments for short notice disruptive possessions and arranged for its sister company, First Bus Glasgow, to accept ScotRail train tickets during these possessions on local bus services.

Network Rail’s contribution was the development of a unique low-cost electrification scheme on the basis that only EMUs will operate below energised overhead line equipment (OLE). As a result, in July the alliance announced its first major project, the £12 million joint investment to introduce an electrified service on the Paisley Canal line by December.

It is interesting to note that Network Rail’s 2010 route plan update stated that development of the Paisley Canal project would start in 2014, so it would seem that the alliance had also accelerated this scheme.

Close to the wire

Brian Sweeney, Network Rail asset engineer for electrification in Scotland, advised that this low-cost electrification scheme was achieved by challenging current practice and specifying the lowest possible wire height for EMU operation. This approach was also used to electrify parts of Thameslink in the 1980s. However, the Paisley Canal scheme has to allow for a possible resumption of a night-time freight service to the Hawkhead Oil terminal – an aspiration for freight operations although there has been no such traffic since 1994. In addition, the Network Change Process commits Network Rail to retain the current W7 gauge.

Although engineering trains may also be outside the ‘EMU gauge’, this is not a problem for Network Rail’s track recording unit and multi-purpose vehicles which can operate with the line energised.

The key was therefore acceptance that freight trains would only be able to run with overhead wires de-energised. This requires a new method of working that allows some trains to operate with power on and others only with power off, which is feasible for the single track Paisley Canal branch line.

Once this decision had been taken, a minimum wire height of 4.030 metres was specified, compared with the minimum ‘standard’ height of 4.165 metres. This provides the required electrical clearance for all ScotRail EMUs, the tallest of which has a dynamic height of 3.870 metres. It also gives a W7 gauge Class 66 locomotive a mechanical clearance under the wire of just 40mm.

Before deciding the wire height, “the man on a platform with an umbrella in Scottish weather” had to be considered. Brian Sweeney explained that, in some circumstances, and with a 4.030 metre wire height, a blown out umbrella could encroach on the electrical clearance. This would not be a problem if designers kept energised OLE equipment away from the platform edge. However, if this was not possible, another method of addressing this risk would have to be found.

Unique Authority Key

Now that the OLE has been energised, there is an entry in the Sectional Appendix stating that only vehicles lower than 3870 mm can use the route. Higher trains are only permitted to run if possessions and isolations are taken. This is an interim solution which is not suitable for any future regular freight train operation.

The permanent solution requires equipment that will release an ‘Authority Key’ once OLE has been ‘de-energised’ and not allow it to be re-energised until the key is replaced. Currently, electrification rules allow for only two states of OLE: ‘Live’ and ‘Isolated’. This method of operation requires a third state of ‘De-energised’, with the power switched off and confirmation that a remote Fixed Earthing Device has engaged correctly. When the equipment is available, this unique method of working will require a freight or engineering train to stop at a notice board to obtain the ‘Authority Key’ before it can proceed. To ensure that the signaller is aware of the special nature of the train, it will be described with an ‘X’ headcode.

Work required

The reduction in specified wire height reduced the minimum required bridge soffit height from 4.44 to 4.305 metres. A soffit height of 4.44 metres would have required track lowering or reconstruction of nine bridges, three of which were at stations. With the revised specification, only five bridges required work, just one of which was at a station. This reduced the number of affected platforms from three to one. One of these bridges was well away from both stations and signals, which allowed the use of an extended neutral section 70 metres long to avoid bridge or track work. The remaining four bridges required track lowering of between 50 and 158mm, with the most significant work taking place at Hawkhead where the station platform was reconstructed at a lower height.

Babcock was awarded a fixed price design and construct contract in June 2012 for all Paisley Canal electrification works with a six month programme. Work commenced in July and was carried out during possessions at weekends and after 8pm on Mondays to Thursdays. Track lowering through three of the foul bridges was undertaken over two weekends in early October using the Medium Output Ballast Cleaner. The track was lowered through Hawkhead station and the platform completely re-built during the nine day blockade.

A rail-mounted Kirow crane was modified to carry a MOVAX vibrating piling attachment. It was coupled to two adapted salmon wagons to carry piles, creating a mini ‘factory train’ that was loaded during the day and installed OLE structure piles at night. Use of the adapted Kirow crane both speeded up installation of the 200 piles and avoided neighbour impact as vibrating piles is significantly quieter than installing them by conventional methods.

On completion of the nine day blockade, all track lowering works had been completed, all OLE masts had been erected and Hawkhead station fully re-built. Work done in the remaining possessions was the final registration of the OLE, completion of bridge parapet works and the installation of mirrors at stations for Driver Only Operated (DOO) EMUs. An additional DOO requirement was testing and commissioning a GSM-R radio system for which ScotRail made a Class 156 DMU available.

As a result of all this work, the OLE on the Paisley Canal branch was energised on 19th November to allow for driver training prior to the start of the electric train service on 9th December.

Cheap and quick

With its first project, the Network Rail / ScotRail alliance has shown what can be achieved when infrastructure owners and train operators work closely together on a project. The alliance has shown that it need not take years to get disruptive possessions and, by focusing on the business requirement, Network Rail’s engineers delivered a scheme that is fit for purpose – no more and no less.

For these reasons, the Paisley Canal Electrification Scheme is both a bargain and a remarkably quick project as it took only 44 days from driving the first pile to having electrified the line. With Network Rail spending over £4 billion on electrification by 2019, it will be interesting to see if this design philosophy is adopted for other passenger-only branch lines.

From canal to electrified railway, the Paisley Canal route has gone through a number of changes. In 2007, a plaque was unveiled at Paisley Canal station to mark the 250th anniversary of its original designer, the great Thomas Telford. He would no doubt have approved of the way that today’s engineers have applied themselves to this latest transition.

David Shirres BSc CEng MIMechE DEM
David Shirres BSc CEng MIMechE DEMhttp://therailengineer.com

Rolling stock, depots, Scottish and Russian railways

David Shirres joined British Rail in 1968 as a scholarship student and graduated in Mechanical Engineering from Sussex University. He has also been awarded a Diploma in Engineering Management by the Institution of Mechanical Engineers.

His roles in British Rail included Maintenance Assistant at Slade Green, Depot Engineer at Haymarket, Scottish DM&EE Training Engineer and ScotRail Safety Systems Manager.

In 1975, he took a three-year break as a volunteer to manage an irrigation project in Bangladesh.

He retired from Network Rail in 2009 after a 37-year railway career. At that time, he was working on the Airdrie to Bathgate project in a role that included the management of utilities and consents. Prior to that, his roles in the privatised railway included various quality, safety and environmental management posts.

David was appointed Editor of Rail Engineer in January 2017 and, since 2010, has written many articles for the magazine on a wide variety of topics including events in Scotland, rail innovation and Russian Railways. In 2013, the latter gave him an award for being its international journalist of the year.

He is also an active member of the IMechE’s Railway Division, having been Chair and Secretary of its Scottish Centre.


  1. One possible alternative that should be considered is to use low height rail. Think short lengths of crane rail under and adjacent to low bridges. At 105 mm high for 100 kg/m rail (KSA 120), this saves 47 mm against 152 mm high 50 kg/m rail. Or 85 mm high for 56.2 kg/m rail (KSA 75), which saves 67 mm.


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