An alternative to installing pantographs with 200mm clearances

The 2019 Railway Industry Association electrification cost challenge report assessed the successes and failings of electrifying the Great Western Electrification Programme (GWEP). Its opening statement stated that the cost of electrification was increased due to factors including “unpreparedness in using novel technologies resulting in poor productivity”. New technologies may seem daunting to the railway; however, the adoption of these techniques is key to adapting, remaining efficient and making improvements.

One such technique is probabilistic gauging. Whilst absolute gauging is safe, tested, and consistent for the railway, this conservative approach can waste millions in unnecessary work. With improvements in dynamic vehicle modelling and up-to-date survey data, gauging is becoming closer to reality than ever before and so offers significant opportunities to reduce both the cost of electrification and gauge clearance work for rail freight. Currently the UK rail network has few routes that can accommodate container trains. Clearing additional routes for such trains is essential if such inter-modal rail freight traffic is to be increased.

Regarding electrification, clearances through our infrastructure are still too tight to safely offer 200mm of clearance between the pantograph and the infrastructure. D/Gauge engineers are well versed in the tolerances and conservatism that are incorporated into absolute gauging to keep the railway safe, but on the second inspection, how can we confidently reduce the space between the OLE and the vehicle, without comprimising safety?

The accident-free history of rolling stock indicated that tolerances are preventing strikes, however it also may indicate differences in expected clearance outcomes in practice versus conservative calculations. Digital simulation is a strong indicator of the vehicle movements, track conditions, and location of OLE equipment. In practice, the track moves over time, rails and wheels wear over time, and loading conditions vary. Tolerances are accommodating for these variations and work to the safest possible outcome.

By assuming that every single element will not be in its worst-case scenario (as is assumed for absolute gauging), secondary analysis can determine more representative in-life clearance outcomes. Rather than use a conventional rule-based approach to gauging, probabilistic pantograph gauging is linked to a ‘Monte Carlo’ event generator which generates ‘events’ where all tolerances are within their prescribed bounds, and which occur within their probability distribution. Alongside the rapid calculation of clearance, we can undertake 10,000 or more simulations and quickly generate probability distributions of the resultant clearances that would occur over this representative lifetime.

As an industry, we choose to take safe, less risky decisions. Balancing risk versus uncertainty is not easily done and changing the status quo can only be done after a thorough investigation and analysis of the consequences of doing something different. To make probabilistic pantograph gauging a success, the industry had to have assurances that new, innovative methods of approaching electrification will not affect risk or safety on the railway.

RSSB commissioned two research projects (T373 – “Uncertainty in Structure Gauging” and T670 – “Investigation of the accumulative effect of vehicle tolerances on gauging”) which specifically analysed “uncertainty analysis”, to investigate tolerances in a mathematically correct manner. The reduction of uncertainty considered how individual tolerances varied, and how they were accumulated as part of a system.

Network Rail Scotland Successes
Since its roll-out with Network Rail Scotland, probabilistic pantograph gauging has reduced the cost of electrification by avoiding bridge reconstructions and so supports the drive to make electrification affordable. A probabilistic pantograph gauging sweep across circa 560 structures in Scotland used modern, probabilistic engineering methodologies to establish where tighter clearances pose actual risks. Combined with VCC overhead systems, (which were extremely successful in the 2018 Andromeda test with Network Rail Scotland), the technologies have reduced the cost of electrification by £187,000 per single track kilometre or £300 million for Scotland’s planned electrification programme which will decarbonise Scotland’s Railway by 2035. Thus probabilistic pantograph gauging brings the business case cost for electrification down and should be used to reassess the real cost of electrification on the rest of the UK network.

Alan Ross, Director of Engineering and Asset Management for Network Rail shared the huge cost savings at the April 2022 PWI conference in Glasgow.

The future of gauging for electrification
Probabilistic pantograph gauging is a comprehensive methodology, specially developed by D/Gauge. Absolute gauging is just as accurate as probabilistic, but its specialism lies in ensuring a higher level of safety and/or demonstrating areas of the network which have no tight clearance spots and OLE can be installed without any considerable disruption or additional costs.

The power of probabilistic lies in assessment in the tight sectors of the UK, where electrification schemes are failing to gain the capital investment to kickstart electrification, or fears of extensive infrastructure works grind work to a stalling stop before they even begin. By utilising the power of novel technologies, more schemes can be reinstated and progressed to move towards the overall goal of electrifying the whole UK Railway.

About D/Gauge
D/Gauge is a 30-strong team dedicated to clearance, including some of the UK’s most celebrated experts in gauging. Its expertise lies in software development, data management, and project consultancy. In 2021 it delivered over 180 projects and over its short history it has worked for 110 clients across the globe.