If real life tolerates 85mm, then perhaps your bridge (for which the best you can get is currently, say, 170mm static clearance), doesn’t need rebuilding.
Might you consider other options? You might look at some of the recent developments in probabilistic gauging, which provides a better estimation of clearances in the real world than you find by simply adding maximum figures for each part of track and train as they move in relation to a structure such as a bridge.
Engineers at Cardiff Intersection Bridge couldn’t easily rebuild it to give the mandated clearance. Here, the main line crossed a river while being crossed itself by another rail line. The answer was a combination of surge arrestors and insulation that NR claims saved £40m.
Several engineers told RailReview that rebuilding bridges cost millions, while surge arrestors came in at tens of thousands. That’s enough to prompt NR to look very closely at what it wants as a client.
For NR’s trans-Pennine and Midland Main Line wiring projects, this switch to surge arrestors (in a technique properly called voltage-controlled clearances, VCC) has removed 80 bridge renewals from those projects’ scope. This includes the challenge of Stalybridge Tunnel, where NR was at one stage faced with a six-month closure.
It’s not just clearances under the bridges that add cost. There’s a requirement to make parapets on bridges crossing over electric railways 1.8 metres high. But simply adding height to parapets can trigger extensive reconstruction if the bridge is not sufficiently strong to cope with the extra load (either the weight or the forces that come from increased wind loading).
Engineers argue that these higher parapets are not proportional to the risks involved (chiefly, electric shocks to pedestrians). Some bridges in some areas will need higher parapets, but (as is so often heard) one size does not fit all.
Both clearance problems are well recognised within NR. Following considerable work, it now suggests bridge soffit heights of 4.25 metres above the rail, rather than the nearly five-metre heights seen in typical Control Period 5 projects.
Thus is NR beginning to shed its reputation as a poor client. This reflects Chief Executive Andrew Haines’ comments to RIA’s annual conference in October 2020: “I see people in Network Rail who are gold-plating schemes in the first instance because our standards have not been driven to reflect a cost-constrained environment.
“I see designers who look to off-load risk from designers to the customer effectively by over-engineering, and that’s a large part of the story for Great Western electrification, and the fact we were a poor client for that doesn’t mitigate the fact of that poor behaviour.”
It’s not just bridge clearances that challenge. The distance from a train’s pantograph to passengers on platforms also matters.
Here, nearby bridges may well push the wires unacceptably low through platforms. One option could be to insulate the outer horns of pantographs where they come closest to passengers. For a railway split between track and train, this answer needs co-ordination between both sides.
Life becomes a bit harder for NR when it comes to deciding what’s wanted from electrification. What trains? What timetable? What power draw?
It’s a question better asked of rail’s controlling mind - supposedly the DfT for the last two decades, but soon to be Great British Railways. But it’s not easy to answer. It depends on forecasts of likely traffic. It depends how efficient the funder wants spending to be. Does that mean installing just enough power for the current service? Or sufficient to provide room for expansion?
Glance back at GNER’s timetable of services from Edinburgh from 1997. There were 21 weekday trains in mid-summer. A handful were diesel HSTs, but most were Class 91 electric locomotives hauling Mk 4 stock, as British Rail introduced when it electrified the route earlier that decade.
Today, GNER’s successor, LNER, runs 28 trains per day south from Edinburgh. All have the ability to run electrically. Add Lumo’s five daily trains (which must run electrically), and TransPennine Express’s four trains (which could and should, but don’t run on electric) and it’s easy to see why NR is busy improving power supplies between Edinburgh and Newcastle.
As NR starts work on wiring the trans-Pennine route between York and Manchester, the question of power is pertinent.
TPE already has a fleet of bi-mode trains, similar to those used by LNER and GWR, so their characteristics are known. But it also runs diesel services along the route, as does Northern. The future for these is less known. As is the future of freight services across the route. NR’s planning provides for more freight paths, but it’s not clear whether they will be diesel or electric.
There should be savings in the way NR brings power to the railway. Rather than classic grid connections, there’s scope to use static frequency converters (SFCs) to feed electricity into the overhead lines. Using SFCs reduced the likely cost of the second phase of the ECML’s power upgrade from £1.3 billion to £400m.
Once there, the power could be fed along OLE that carries higher mechanical tension, which in turn allows masts to be spaced further apart. This cuts the number of masts and foundations needed - albeit the masts and wires might need to be beefier to cope with the higher tension.
Siemens suggests that its SICAT range could stretch mast distance from today’s 65 metres to up to 80 metres, and perhaps even 110 metres with its SX range, although it’s not approved for UK use.
Perhaps this is the sort of innovation that Andrew Haines meant when he addressed a Permanent Way Institution meeting last year: “Critical to future electrification will be a relentless wave of innovation and collaboration to make it more affordable. That demands a different approach from the one Network Rail has relied upon in the past. It demands a different sort of contractual relationship and a different sort of appetite from the supply chain to offer up innovation.”
While Bill Reeve in Scotland senses urgency in replacing ageing diesel trains with new electric stock, in England there is less pressure.
English operators such as Northern face the same challenges. It still runs the same ‘156s’ and ‘158s’ that Reeve’s ScotRail operates. Northern’s are just as old, but there’s no talk of wiring Newcastle to Carlisle for its roughly three trains each way every hour, for example.
Yet Haines is clear about the importance of electrification within decarbonisation. He told that PWI meeting last year: “Decarbonisation is one of our biggest opportunities and one of our biggest challenges. We get our approach right and we secure the future of our country’s railways as the UK’s greenest form of mass transit for generations to come. If we get it wrong, we lose ground to our competitors and throw away one of the railway’s major selling points - its sustainability.
“I was pleased to see the government support and (I quote) ‘ambitious, sustainable and cost-effective programme of electrification’ in its transport decarbonisation plan. But it would be a massive mistake to think we now have a blank cheque to decarbonise the remaining 60% of our railway.
“The ball is now firmly in our court to demonstrate to government that the railway is capable of delivering value for money for every pound spent on decarbonisation.
“Demonstrate that we have learnt from the lessons of the past. It would be stupid to underestimate the damage that has been done by the cost and schedule overruns on the Great Western electrification, to name one project. Demonstrate that we can be trusted to deliver on schemes efficiently and at reduced cost.”
Measure twice, cut once. ■
