Last year, the Aberdeen to Inverness Improvement Project (A2I) redoubled 8.5km of track between Aberdeen and Dyce as reported in issue 168 (October 2018). However, this redoubled track could not carry any passenger trains until this year’s completion of the 25.5km Aberdeen to Inverurie redoubling work in August on which we report this month.
The completion of this redoubling marks the end of phase one of the A2I programme which, as reported in issue 158 (December 2017) included earlier work to provide a relocated station at Forres, on a new straight 1.25km loop, and work at Elgin, which included platform extensions, the provision of a turnback facility and extension of the loop from 650 metres to 1.5km.
This work was completed in October 2017. It also included signalling and telecommunications improvements which saw the section of the line from Inverness to Keith controlled from a new Highland workstation at the Inverness signalling centre.
Prior to that, telecommunications enhancements provided a new multi-protocol label switching (MPLS) transmission network to support operational and station systems along the route. This required further network upgrade works both between Aberdeen and Dundee and between Inverness and Perth to ensure diverse routing. Other telecommunications work included the provision of an internet protocol telephone concentrator at Inverness, for the user-worked crossing phones previously controlled by the closed signal boxes, and the alteration of GSM-R call routing due to the transfer of control to Inverness.
The investment of £330 million on A2I phase one follows the 2009 Scottish Government Strategic Transport Projects Review, which concluded that A2I was one of Scotland’s top four transport priorities. Over the past ten years, there has been an 87 per cent increase in patronage between Inverness and Aberdeen with most of this increase between Aberdeen and Dyce (146 per cent) and Inverurie (247 per cent).
Journey time over the 173-kilometre-long Aberdeen and Inverness route is around 2 ¼ hours with an irregular, about two-hourly service frequency. At each end of the route there is also a roughly hourly local service between Inverness and Elgin and between Aberdeen to Inverurie.
Whilst the Scottish Government’s long-term objective for the Aberdeen to Inverness line is the provision of an hourly service with a two-hour journey time, A2I also delivers the more immediate requirement of improving local services at either end of the line and the provision of additional stations at Dalcross and Kintore without affecting journey times. For this reason, the provision of the proposed new station at Dalcross will require the provision of a new two-kilometre loop.
Both these stations are subject to separate funding agreements. For Kintore, this was agreed between Transport Scotland, Aberdeenshire Council and North East Regional Transport Partnership (Nestrans) and the £14.5 million contract for the station’s construction was awarded to BAM Nuttall in May. This enabled much of its construction to be done during the 2019 blockade.
Although planning permission has been agreed for Dalcross station, arrangements for its funding have yet to be finalised.
The 2018 blockade
The track laid last summer between Kittybrewster and Dyce was the first stage of the redoubling of the line between Aberdeen and Inverurie. The new double track starts at Kittybrewster, 1.5km from Aberdeen station, as redoubling the Hutcheson Street and Schoolhill tunnels would have required track lowering at significant cost and was not necessary for a 15-minute service.
This involved much more than just putting the track back as, since it was lifted in 1968, numerous assets have been placed on the track bed, the single line now followed the double trackbed racing line and some underbridges only had a single-track deck. Moreover, the original earthworks cannot accommodate a double track in accordance with current standards and this largely built-up section required significant neighbour engagement as a result of tracks being laid closer to adjacent houses.
Earthworks retention was therefore a large part of the work. This was achieved by interlocking concrete blocks, high friction fill material or king-post retaining walls. These use H piles driven to pre-determined depths into the ground with timbers inserted between the webs of the H section.
For these reasons, redoubling this 26km corridor required significant reconstruction of the railway corridor, for which a blockade was the only option. As it was considered unacceptable to close the railway for the six months that this would take, it was decided that it would be done in two summer blockades, each of about three months, with the loop at Dyce enabling the redoubling to be staged into two parts.
On completion, the newly laid track was left unused, which presented an unusual signal-sighting problem as the new Up line could not be used by trains until the end of the 2019 blockade. Until then, what was to become the Down line remained as the single bi-directional Up/Down line. This meant that, until the 2019 commissioning, some signals for Up direction trains were relocated as temporary signals to the right of the single line as the new Up line prevented them being located on the left. These temporary signals were replaced by new permanent signals on the left of the new Up line during the 2019 blockade.
With the newly laid track left unused, the operational railway was essentially unchanged by the 2018 blockade and therefore did not require significant signalling work. This also meant that it was only necessary to bus passengers between Aberdeen and Dyce, as Dyce station could stay open during the blockade.
The 2019 blockade
Contractual arrangements for this year’s blockade were the same as for other A2I phase one works in that Network Rail engaged Siemens for the signalling and telecommunications work and BAM Nuttall for everything else. BAM Nuttall’s main sub-contractors were AECOM and Jacobs for design, Babcock for track work and Stobart Rail for ancillary civil engineering work.
This year’s blockade was from 4 May to 19 August and differed significantly from last year’s work. It laid nearly 15km of new track, almost twice that of last year’s blockade, though the complication of the racing line was not such a significant issue this time. Furthermore, instead of being in an urban area it was largely through farmland and so had various level crossings to contend with.
The programme required a large amount of bridge works, including two underbridge replacements, seven underbridge bridge extensions, one infill, strengthening six underbridges and the removal of two overbridges. This year’s blockade also required significant work to strengthen the five-span viaduct over the River Don, just south of Inverurie.
Advantage was also taken of the blockade’s extension to Huntly, as described below, to extend the short platforms at Insch to 160 metres to accommodate ScotRail’s Inter7City sets. These are the newly refurbished five-coach High Speed Trains which now serve Scotland’s seven cities.
The 2019 work also involved work on the existing railway at both ends of the new double track section which meant changes to the replacement buses during the blockade. For the first six weeks, the bus replacement services were between Dyce and Inverurie, then buses ran for another eight weeks between Dyce and Huntly, where temporary welfare facilities had to be provided for train crews. The final nine days of the blockade saw buses between Aberdeen and Inverness for three days and then six days of buses between Aberdeen and Huntly.
Rail Engineer visited the redoubling works on 17 July during week 11 of the 15-week blockade and had an opportunity to tour the site with its programme manager, Colin MacDonald, at BAM Nuttall’s project office and compound at Inverurie. This site office also includes ‘Hotel BAM’, which provides temporary accommodation for around thirty and has a fully equipped gym. With a shortage of hotels in the immediate vicinity, this is a cost-effective way of accommodating the workforce.
Building this temporary accommodation is one solution to the problem of the project being a three-hour journey from Scotland’s central belt, where many of its project personnel are based. For example, as well as overseeing the work on site, the Network Rail project team must liaise with engineers, designers, operational planners and others based in Glasgow.
Touring the work
The tour started at the newly laid S&C by the Inverurie project office. This is the western limit of the new double-track section, where a new turnback facility has been provided capable of accommodating ScotRail’s Inter7city sets. Two synchronised S&C tampers were seen working together to simultaneously tamp the ballast under the crossing bearers.
At the Don viaduct works, Colin explained that this presented significant challenges in view of the requirement to avoid putting significant additional weight on the substructure, as this would have required costly in-river work and could have delayed the project. For this reason, the ballasted track option, which would have added 2,000 tonnes to the weight of the bridge, was rejected. Rails over the viaduct have therefore been laid on longitudinal timbers in new timber cradle units.
Works to strengthen the viaduct were viewed from a temporary crash deck below the bridge superstructure. These included the replacement of all cross girders – replaced by deeper ones – and additional plating on the side beams. The abutments had also been strengthened to resist the worst-case scenario of the force of a braking ballast train. Further protection against such forces is provided by shock absorbers that have been installed at the pillars and abutments.
Next stop on the tour was a bridge overlooking the station work at Kintore. When built, this will be an unmanned station with a 166-space car park. The station is immediately adjacent to the A96 dual carriageway, so it is expected to be a busy park and ride station. Colin explained that, although this was a separate contract to the main blockade works, its construction was an integral part of the project as a whole. With limited access to the north side of the line, it was important to make best use of the blockade to construct the north-side platforms.
Nearby, Boat of Kintyre level crossing was being upgraded from a single line AHB (automatic half barrier) to a MCBOD (manually controlled barriers obstacle detection) double-tracked crossing. The signaller’s workload was a significant factor in the choice of the MCBOD crossing as this does not require the close study of CCTV images to determine when it is safe to lower the barriers.
This level-crossing work required a road closure for the duration of the blockade, with only pedestrian access across the railway. It also needed extra land by the crossing for its equipment housing, which had to be built on most of the garden of the adjacent house that the owner had agreed to sell.
The A2I redoubling works also required the upgrade of three user-worked crossings and the closure of two more – as a result of arrangements negotiated with those affected, this included the purchase of a house that could only be accessed by the crossing.
Another deal had to be made to allow the demolition of the paper mill bridge near Inverurie, the central pillar of which would have obstructed the double tracking. Colin noted that, although it is normally possible to reach suitable agreements with those affected, such issues present significant risks to major projects, such as A2I, that have no compulsory powers. There may not be an alternative design solution if someone doesn’t wish to sell their land under any circumstances, a situation which could cause major problems.
The last call on the guided tour was to see the retention work at Kinaldie, where king-post retaining walls could be seen supporting the embankment to the east for a kilometre or so, a clear indication of the work required to replace a track lifted fifty years ago.
Programming the blockade
To allow track laying to commence at the start of the blockade, almost all the civil works required for track laying were completed beforehand. This included retention work that could safely be done whilst the single line was open. Night-time ‘rules of the route’ possessions were used for work that affected the track support zone or had plant and equipment that could not be safely separated from trains.
Other than the Don viaduct, the only bridgework done during the blockade was the re-decking of underbridge 67 over the old canal, immediately south of the viaduct.
Disruptive possessions from 20 to 22 April (72 hours) and 27/28 April (54 hours) saw work done on six underbridges, including deck renewals and extensions, retention earthworks, track formation work and ancillary civils works. The latter was sequenced to give priority to the subsequent work (equipment bases and the troughing between them) so that cables could be run out.
In this way, most of the lineside signalling infrastructure was completed prior in advance, which was key to allowing track installation to commence from the outset of the blockade.
Track laying used a seven-sleeper spreader beam to lift sleepers from wagons and place them into position with the correct spacing. Continuously welded rail, which had previously been laid alongside the existing single line, was then thimbled into position by road-rail vehicles and clipped up by a fastclipping machine.
The programme required the completion of all work requiring engineering trains and road-rail vehicles by 13 August to support the final phase of signalling commissioning and associated wheels free testing. The new double-track railway was commissioned in the early hours of 17 August to allow three days of familiarisation runs for the route’s 176 drivers, with the passenger service resuming on 20 August.
Signalling black hole
Prior to the blockade, signalling between Aberdeen and Inverness was controlled by Aberdeen signalling centre, mechanical signal boxes at Dyce, Inverurie, Insch, Huntly and Keith, and the Inverness signalling centre’s Highland workstation, which was commissioned as part of the October 2017 A2I works.
The 2019 blockade saw the closure of Dyce and Inverurie signal boxes with control of the line from Kittybrewster to Insch transferred to the Highland workstation. The long-term aspiration is that this workstation will eventually control the route throughout. However, for now trains between Keith and Insch disappear from the Highland workstation panel only to reappear about an hour later.
This recontrol required the modification of interlockings, changes to train describers and the provision of fringe controls at Insch, for Inverness’s Highland workstation, and at Kittybrewster for the NX panel at Aberdeen signalling centre. Control of the blockade’s level crossings, as well as the sidings at Kittybrewster and Raiths Farm, were also transferred to the Highland workstation.
The new signalling equipment includes 51 signals, many of which are single lens LED colour lights, and nine new switch and crossing units. It is controlled by Siemens Westrace interlockings and train detection is by a combination of 92 newly installed Frauscher axle counters and some DC track circuits between Aberdeen and Dyce.
Job done
Completion of the blockade marked the end of the Aberdeen to Inverness phase one works. 25 kilometres of track had been laid on 39,000 sleepers using 110,000 tonnes of ballast, of which 20,000 tonnes was recycled ballast. Laying this track required the removal of 20,000 tonnes of spoil and the provision of 5,000 tonnes of engineering material, along with 27 kilometres of embankment retention. The signalling work also required over 137 kilometres of cables.
Impressive though these statistics are, what counts for passengers is the extra train services, made possible by this project, that ScotRail will introduce during the December timetable change. A total of 20 additional services a day between Aberdeen and Inverurie will provide a minimum of a half-hourly service – every 20-minutes at the peak. ScotRail will also introduce a new Montrose to Aberdeen service that, in most hours, will be extended to provide a Montrose to Inverurie service.
At the other end of the line, an additional six Elgin-Inverness services will add to the nine such services introduced in December 2018, giving Elgin an hourly all-day service. Those who wish to travel longer distances from stations on the route will also benefit in December from the provision of six through services from Inverness to the central belt of Scotland via Aberdeen.
It has taken four years to deliver A2I phase one – one of the UK’s longest redoubling projects – as well as a series of enhancements to provide more-efficient loop operation. On a single-track railway, this is perhaps likely to offer greater time savings than line speed enhancements.
As Inverness to Aberdeen is the only UK inter-city rail service operated largely over a single track, it’s good to see serious money spent on such targeted enhancements. It will be interesting to see how phase two can bring further improvements.
This article first appeared in Issue 177 of Rail Engineer, Aug/Sep 2019.
