The current HS2 proposal (phase 1) is for a new 2 track railway from Lichfield and Birmingham to London. What would be the impact of building the new line as 4 tracks?
A four track HS2?
HS2 is currently designed as a 2 track railway from London to the Midlands and the North. Current plans for services show 18tph (trains per hour) on the first London to east Birmingham section, a level which many rail experts consider to be difficult to achieve.
Widening the railway to 4 tracks between London and the junction east of Birmingham would clearly provide a greater number of train paths, allowing 36tph based on the current plans. However, with twice as many tracks to spread over, it would be more reasonable to plan for slightly less, say 32tph, in order to provide more resilience in the event of disruption.
There would seem to be a variety of options with real benefits that the paths could be used for.
Heathrow. Phase 2 of HS2 is supposed to include a direct link to Heathrow airport. The problem is that there is no spare capacity (in tph) to actually provide any through trains! With a 4 track HS2, there could be 4tph to east Birmingham, with those services continuing once per hour to each of Manchester, Glasgow, Leeds and Birmingham. This approach would make even more sense if the Heathrow line actually continued to somewhere on the South West or South of London.
Europe. The desire for through services to Paris and Brussels is undoubtedly there, but the 18tph limit of 2 tracks does not allow these through services in the peak without compromising services elsewhere. A 4 track HS2 would provide enough paths for at least 2ph direct from the continent.
Aylesbury. A link could be built from the HS2 line to the existing line at Aylesbury. This would solve a key problem HS2 faces in that it currently passes through the Chilterns without providing any benefits to local residents. A 4 track HS2 together with a new junction would allow a fast commuter service to Aylesbury. Potentially, this could run through to Kent on HS1 and on to Milton Keynes via the reopened route to Bletchley.
Warwick area. A link could be built to connect the HS2 line to the existing line to Leamington Spa, allowing through London services to Warwick, Coventry and Solihull. Again, this service might run through from Kent.
Towns in the North. The additional trains-per-hour capacity would also permit through services to destinations HS2 currently intends to miss out, including Stoke-on-Trent, Derby, Blackpool and North Wales.
Oxford area. A north-facing link could be built to connect the HS2 line to the existing line north of Banbury, allowing through services from Manchester and Leeds to Oxford, Swindon, Bath and Bristol. This link is one of the most important missing elements of the current plans, as current HS2 plans make journeys from Oxford and Banbury to Manchester and Leeds significantly worse as existing Oxford services serve Birmingham New Street, but the new HS2 services to Manchester and Leeds go from Curzon Street. This connection also spreads the benefit of HS2 over more of the country, making the spending fairer to the South West.
But what about the London terminals?
Clearly it is not possible to almost double the amount of trains on the line without addressing where they might go in London. However, a careful reading of the above indicates that most services could be routed to Heathrow or Kent, avoiding terminating in London. For the remaining services it may be necessary to terminate at Old Oak Common.
But what about the cost?
Well undoubtedly building HS2 with 4 tracks is more expensive than building with 2 tracks. And there is extra cost in the additional junctions. But the relative cost compared to building a second high speed line to the North (something which is talked about in railway circles) is much lower. The benefits of greater integration with the existing rail network is also a huge factor.
But what about the land used?
Building 4 tracks rather than 2 tracks will be a relatively minor change to the land take of the project. Cuttings and viaducts would be twice as wide in terms of the track itself, but the width of the slope of the cutting/embankment would need no more width. The main pain would be the tunnels, which would generate twice as much spoil.
Is it a good idea?
Ultimately, HS2 is a political decision. While I have grave doubts about the HS2 approach to new lines in general, I'm also trying to ensure that HS2 is the best it can be if it does go ahead. Making it a 4 track railway to east Birmingham would have clear benefits. So, in my opinion it is definitely a good idea and improves markedly on the current scheme.
But those benefits can only be realised if 4 tracks is built from the start. Once constructed, it is likely that Old Oak Common will be unable to be expanded (as there will be a large development built on top). As such, the argument for 4 tracks must be discussed sooner rather than later.