HS2 and slab track
As well as renewal of the train fleet, the modernisation of Merseyrail includes track, station, and depot upgrades. Renewal of slab track in the unidirectional loop line under central Liverpool is programmed to take place between January and June 2017 in a three-phase process involving protracted closure of the loop and the use of rail-replacement buses.
[‘In 1977 the loop line opened – now it’s time to renew the track’. 3rd January – 18th June 2017, Merseyrail and Network Rail]
Why does the work need to be undertaken?
A total 1.2 km length of concrete track slab – the seven most challenging sections on the ‘loop’ – needs to be replaced for the first time since the loop was opened in the 1970s to ensure that the network remains reliable and safe. Meanwhile, other work is taking place to make the most of the closure. 1100 yards of traditional ballasted track is being replaced under the riverbed as well as other maintenance jobs being carried out, such as the repair of broken sleepers and work to realign track as well as renewal work to switches and crossings which the Merseyrail trains use to switch lines. Doing all this work in one go means that passengers are less likely to be inconvenienced in future. The new track slab is expected to last for up to 60 years.
The old loop slab track ‘needs replacement after 40 years’, but the new slab is expected to last ‘up to 60 years’. So how long was the old slab ‘expected to last’?
According to a September 2016 story from New Civil Engineer, a decision on whether to use slab track on HS2 phase one was ‘expected in November’ (2016).
[Slab track confirmed for High Speed 2, Mark Hansford, NCE, 23 September 2016]
Speaking at New Civil Engineer’s Future Tech Forum Mark Morris, High Speed 2’s director of asset management, railway operations said that the first London to Birmingham phase of the £32 bn rail line was set to be built using a concrete slabtrack system, with a ballasted track bed set to be favoured for phase 2 from Birmingham to Leeds and Manchester.
The choice of trackbed technology has been the subject of heated lobbying. Proponents of slabtrack system have argued that ballasted track systems are noisy in use, expensive to maintain and even pose safety risks with individual ballast particles liable to be dislodged by the turbulent air caused by the passing high speed trains.
Conversely advocates of ballast-based systems point to the much lower cost and flexibility in use afforded by such systems.
400-odd km of HS2 slab track would be much more intensively used than Merseyrail’s “1.2 km”. So how long would it last? When it needed replacing, how could HS2 continue to operate?
Digging out and replacing sections of high speed rail track slab is not really a ‘weekend job’, is it?