How fast could trains realistically run in the UK?

[Anetos]

I know that HS2 is designed for 225mph trains which is pretty fast, but what about practically on existing rail infrastructure?

 

[Sun Chariot]

I know that HS2 is designed for 225mph trains which is pretty fast, but what about practically on existing rail infrastructure?

There's a reason why HS1 was built and HS2, in its truncated form, is being constructed.

Existing lines are limited by: signalling types and distances, track geometry and alignment, capacity, pathing with other trains (stoppers, semi fasts and, where relevant, freight).

And trains themselves: power needed to reach and maintain 225mph; and braking capabilities to slow rapidly and safely.

 

[Zomboid]

Isn't the record on the classic network something like 163mph?

If you wanted to throw money at it then I imagine some sections of the ECML would handle 150mph without too much trouble. And if you don't want to make any infrastructure changes it'll be 125mph.

 

[Sorcerer]

On existing infrastructure the best you could hope for is probably 140mph. Usually any services running above that speed have specially dedicated and newly built infrastructure, but there are exceptions to this such as the Amtrak Acela on the Northeast Corridor in the US and British Rail's original plans for 155mph APT. All of this assumes you have the appropriate cab signalling equipment of course. Nevertheless, such line speeds eat up capacity on mixed-traffic railways with freight and local services, so it's not optimal to run above 125mph on the conventional network.

 

[stadler]

I am pretty sure there was a couple of cases of IETs (800/801/802) overspeeding and reaching almost 150mph in their first few years of being introduced. So i suppose theoretically you could probably increase some major lines to 150mph if you wanted to. I doubt that this would ever officially be approved though as there would probably be too many safety concerns.

 

[Ken H]

Why is 125 the max speed for a line with no in cab signalling? Why not 130? Is it just because BR specified HST as a 125 mph train and thats been cast in stone? Has any one done a cost benefit analysis of the small speed increase?

 

[A S Leib]

The time difference between 125 mph and 130 mph is around one second per mile, so even for something like Bristol Parkway to Paddington the time saving would be around a minute and a half. I don't know if the cost would be small enough to justify that.

 

[mike57]

Is it just because BR specified HST as a 125 mph train and thats been cast in stone?

I suspect thats the case, my understanding is the HST was able to acheive similar braking distances at 125mph to a conventional loco hauled service at 100mph. So actual infrastructure changes were fairly minor. Diesel powered, so no power pick up issues. This was why is was a success, a step change in improvement in journey times, with no major infrastructure upgrades.

They did play around with 140mph and a flashing green aspect on the ECML to allow 140mph running, I am pretty sure that the trials came to the conclusion that 140mph, which is probably the next step after 125, is where issues with things like signal sighting become an issue. So that led to the current 125mph maximum using conventional signals. I think this was what canned the proposals to run at 140mph which was part of the original WCML upgrades when the Pendelinos were introduced. There were also cases of HSTs exceeding 125mph regularly during the earlier days. I was once on a slightly late running service from Newcastle which made up significant time, with some very fast running south of Northallerton, I have no actual data (it was 1981, pre GPS obviously) but my 'feeling' is we probably hit 135mph maybe a bit more. But a one off run, on a fine early spring day is very different to running in all weathers and conditions day in day out. Ignoring the rule book common sense says travelling at 135 on this stretch on a fine day when the driver can probably see not only the next signals, but probably the next one or two is a very different risk than doing the same thing on a wet winters day with poorer visibility.

Its not impossible to imagine limited 140mph running under conventional signalling in a few select locations, with an obvious thought being York - Northallerton, but the infrastructure/signalling changes are just not worth the cost to save a minute or two.

The APT program pretty much determined that with conventional track spacing ~150mph is the practical limit for two trains passing, I think the Selby diversion was engineered for this sort of speed, I dont know if track spacing is wider than normal (even if only by a bit).

So on conventional lines I dont think we will move up from 125mph. Too much cost for too little gain. Obviously dedicated high speed lines are different, the French have already proved that 350mph is achievable, but not necessarily practical for conventional wheel on track technology. That was the subject of another thread a few years ago, I wonder at what point the rail wheel interface slips, as you go faster you have to apply more torque to accelerate and maintain your speed, and there must come a point where this torque is greater than the rail wheel interface can handle, and thats a physical limit set by the technology, but I have no idea what that speed is beyond knowing that it is more than 350mph...

 

[Western Lord]

On our crowded island few trains these days make long non stop runs. If you want to maximise capacity you should reduce the difference between fastest and slowest trains, not increase it. It also requires a lot of energy (i.e. cost) to accelerate a train to high speed.

 

[Railcar]

When Southern trains bound for coastal resorts arrive a few minutes late on Platform 3 of East Croydon, the drivers will take it easy to Stoats Nest Junction, accelerate to Star Bridge, then use the welded rail of the Quarry Line to push their 8-coach 377s up to line speed to make up time to Gatwick and then to HHE. Is line speed on the Quarry Line 70mph? The houses and countryside flashed by on my last journey to Eastbourne

 

[30907]

When Southern trains bound for coastal resorts arrive a few minutes late on Platform 3 of East Croydon, the drivers will take it easy to Stoats Nest Junction, accelerate to Star Bridge, then use the welded rail of the Quarry Line to push their 8-coach 377s up to line speed to make up time to Gatwick and then to HHE. Is line speed on the Quarry Line 70mph? The houses and countryside flashed by on my last journey to Eastbourne

SR suburban area default speed limit is 60 (there are some 70 sections) , otherwise 90 (where permitted), the change used to be at South Croydon.
I would expect the Quarry to be 90, but don't have the sectional appendix to hand.

 

[hexagon789]

When Southern trains bound for coastal resorts arrive a few minutes late on Platform 3 of East Croydon, the drivers will take it easy to Stoats Nest Junction, accelerate to Star Bridge, then use the welded rail of the Quarry Line to push their 8-coach 377s up to line speed to make up time to Gatwick and then to HHE. Is line speed on the Quarry Line 70mph? The houses and countryside flashed by on my last journey to Eastbourne

SR suburban area default speed limit is 60 (there are some 70 sections) , otherwise 90 (where permitted), the change used to be at South Croydon.
I would expect the Quarry to be 90, but don't have the sectional appendix to hand.

It is 90mph.