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Friday, June 25, 2021

Straight down the middle

It might not be on quite the scale of the West Coast Main Line upgrade but there’s a rail corridor in Scotland that is every bit as busy and is set to be completely rebuilt. The six-mile double-track railway between Glasgow Central and Paisley Gilmour Street handles more than 300 trains every day and forms a notorious bottleneck to services operating on the Ayrshire Coast and Inverclyde lines. During the course of 2011 it is to benefit from a dramatic route enhancement scheme.

Issue 68 of the rail engineer reported on the construction of two new platforms at Glasgow Central – the biggest improvement to passenger facilities at the station since 1906. In reality, this formed an early stage of what has become known as the Paisley Corridor Improvement (PCI) scheme. Born out of the cancelled Glasgow Airport Rail Link (GARL) project, PCI involves a lot more than some additional platform space. Although the Scottish Government cancelled GARL’s 1.2-mile airport branch in September 2009, it was agreed that the crucial capacity benefits that the project brought to the existing rail network should still go ahead. These works would also tie in with the implementation of a complex resignalling scheme to be delivered by Network Rail on the lines west of Glasgow.

The proposed solution

In essence, the PCI scheme involves an upgrade from two tracks to three bi-directional lines on the section between Shields Junction in Glasgow and Arkleston Junction, one mile east of Paisley Gilmour Street Station. To the west of Arkleston, four bi-directional lines will be provided, making use of the formation presently occupied by Up & Down Goods loops. The new lines will extend through the four platform faces at Paisley Gilmour Street, eliminating the existing double-track Wallneuk Junction located immediately east of the station where the Ayrshire Coast and Inverclyde lines diverge. Currently this forms a critical capacity pinch point.

Two complex sets of crossovers, at Wallneuk and Arkleston, will provide the flexibility needed to make full use of the bi-directional three-track corridor. New crossovers will also be installed at Ibrox on the three-track section, allowing access to the Deanside freight branch, and at Gower Street Junction near Shields.

Bill Lynas, Network Rail’s project sponsor explains the thinking. “Although all the running lines between Shields and Paisley will be bi-directional, only the new central track will be used in reversible mode on a daily basis. Bi-directional signalling on the existing Up and Down lines will however facilitate the implementation of a much more efficient maintenance regime. We’ve given much thought to the new layout, which we think is as flexible as it can be within the existing land constraints.”

Possession agreement

The Paisley corridor formation was originally four-track but this was reduced to two when the route was electrified in 1967. Returning the full route to four tracks was not so easy though. “The business case could not be made for the reinstatement of a four-track route”, continues Bill. “Modern standards dictate that more land is required than in former years, partly to provide positions of safety for track staff but also as we have to accommodate OLE stanchions. Also, in the Ibrox and Cardonald areas, the M8 motorway has encroached onto former railway land. We are confident however that the chosen three and four-track bi-directional layout will provide sufficient capacity for at least the next 30 years.”

This has in fact worked greatly in Network Rail’s favour as the wide separation of the existing tracks means that it is relatively simple to insert a third running line between them. It also means that very little work needs to be undertaken at the three intermediate stations, Cardonald, Hillington East and Hillington West. Problems still abound however, as Bill explains. “We must undertake this work, with all of the necessary connections to the existing two lines, on one of the busiest routes in Scotland. Getting access to do the job but still keep the railway running is therefore a considerable challenge, but we’ve done a lot of preparatory work on this and have reached agreement with the train operators on the implementation of the necessary possessions.”

A736 Bridge
The A736 bridge at Hillington required an additional centre span

Minimising disruption

Over Christmas 2010, an important enabling component of PCI, a new trailing crossover, was installed at Brown Street in Paisley. Bill outlines the reasons for the work. “Although Brown Street is strictly beyond what we know as the Paisley corridor, the new crossover provides the key to both the main corridor works, which will take place throughout 2011, and also the subsequent operation of the completed project. This is because it will enable trains from Ayrshire to turn back at Platform 3 in Paisley Gilmour Street at times when the onward route to Glasgow Central is blocked by the construction of the project. It will also help to unlock the bi-directional capability of the completed route.”

In order to minimise customer disruption, the Brown Street crossover was installed over a 54-hour possession on Christmas Day and Boxing Day, there being no booked traffic on the former and a much-reduced service on the latter. Situated approximately 350 yards along the Ayr line from Paisley Gilmour Street, the crossover was incorporated into the signalling system on New Year’s Day.

“Network Rail has gone to considerable lengths to minimise the extent of disruption needed on the Paisley corridor to construct PCI”, explains Bill. “The very nature of converting a very busy two-track railway into three and four tracks inevitably requires a lot of construction access. Options for a blockade approach were discounted at an early project stage due to the critical importance of the corridor to commuter traffic from Ayrshire and Inverclyde into Glasgow.”

Weekend working is the chosen alternative but this will require some form of access almost every weekend during 2011. That said, the level of access needed in the final project programme is some 40% less than that thought necessary at the feasibility stage, despite more work now being done. This improvement in the efficiency of access has partly been achieved by planning the majority of Sunday possessions for 11 plus 8 hours duration rather than the traditional straight 29 hours. In this way, the railway is restored to traffic for the busiest part of the day, from late morning until mid evening, thus minimising the disruptive effect for the majority of customers.

Making preparations

A key component of PCI was completed as long ago as the end of 2009 – again, not in the Paisley corridor itself but on the line to Kilwinning and Ayr. It involved the extension of the Up loop at Elderslie. Now bi-directionally signalled, it can be used to recess the longest of freight trains. It has taken on the functionality of the Up loop at Arkleston which was closed in December to make way for the four-track section to be installed under the main PCI works.

Other preparatory works completed during 2010 included the addition of a third span to the Sandwood Road (A736) bridge at Hillington, plus the refurbishment of the two existing spans. In addition, some 71 overhead line portals have been installed between Shields and Paisley, as the original cantilevered structures were located in the centre of the formation where the third track will soon be.

Paisley Hy-Drive units
The completed crossover with its Hy-Drive units

Who, what, where

In order to maximise delivery efficiencies, the Paisley Corridor enhancement works have been combined with a major signalling renewal, the contract for which has been awarded to Invensys Rail. It will be completed to the same timescales as PCI and, as well as covering all of the corridor itself, will also include re-control of the Ayrshire and Inverclyde routes to the new West of Scotland Signalling Centre (WSSC) at Cowlairs in Glasgow. WSSC was commissioned in December 2008 as part of the Glasgow Central Interlocking Renewal project.

During the course of 2011 the PCI resignalling scheme will reach two milestones. Firstly, the existing relay interlockings at Shields and Cardonald will be renewed as a single WESTLOCK computer-based interlocking located at Shields, with commissioning due to take place in July. This will be followed by the installation of a similar interlocking at Paisley, resulting in the closure of the Paisley Signalling Centre. Commissioning of this second phase is scheduled to take place during a 126-hour possession starting on Christmas Day.

Although Invensys Rail is the principal signalling contractor, GE Transportation Systems using its Sapphire T48 Modular Control System will install the new workstations within the WSSC. All of the new signalling will be four-aspect, using LED signal heads. Unusually for the area, point actuation will be my means of Network Rail Hy-Drive installations – a combination of in-bearer Clamp Locks and Alstom SO hydraulic back drives (see issue 54 of the rail engineer).

The full package of PCI works, including the resignalling, is valued at £169.8 million. It is being financed by Network Rail following an agreement with Transport Scotland that it should be included amongst Control Period 4 outputs. Balfour Beatty Rail has been awarded the ‘design & build’ contract for the non-signalling components.

Service enhancement

First ScotRail intends to operate its new Class 380 EMUs on both the Ayrshire Coast and Inverclyde routes and platforms at several stations have already been extended to accommodate these longer units (see issue 72 of the rail engineer). They are currently working closely with Network Rail and Transport Scotland on options for an enhanced timetable, making full use of the new trains’ capabilities and the increased capacity provided by PCI. The infrastructure works will be completed in January 2012 and the new timetable is likely to be introduced the following December.

Ayrshire is a highly popular residential area and has a substantial population choosing to work in Glasgow. The relatively long commuting distances into the city provide valuable fare revenue but of course those passengers expect a decent service; that’s the whole point of the upgrade. Linespeeds will remain at 75mph through the Paisley corridor itself and 90mph on the Ayr line but it is thought that journey time improvements will still be achievable by reconfiguring the timetable.

The level of railway investment in Scotland remains impressive and proves that the environmental and sustainability objectives of the Scottish Government are feeding through to tangible projects. From an engineering perspective, the words flexibility, adaptability and maintainability come to mind when looking at PCI – surely the hallmarks of any great piece of railway infrastructure design work.

With the scheme now in its final year, the Paisley corridor will soon be the latest to benefit from our engineers’ efforts. With other enhancements in the pipeline such as the Edinburgh-Glasgow Improvements Programme, Scotland continues to lead the way in making its railways central to a sustainable future.

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