Why is the proposed top speed of HS2 360km/h?

[Transilien]

In most places 300km/h is the standard top speed, so why is HS2 (being short in length for a high speed line) have a top speed of 360km/h?

 

[SynthD]

They spoke to the planners and operators of high speed rail in other countries. The most important piece of advice was to build it capable of faster speeds than they intend to start with. It's been descoped in length and speed, but I think the intention is still to speed up later. While the regular speed is 300, trains trying to catch up can go 330.

 

[hexagon789]

In most places 300km/h is the standard top speed, so why is HS2 (being short in length for a high speed line) have a top speed of 360km/h?

Most high-speed lines have a higher design speed than service speed. The newer 320km/h LGV lines in France were built with a profile suitable for 350km/h.

There is an element of ensuring some future proofing.

The original French LGV, the Sud-Est from Paris to Lyon was originally 270km/h throughout (trains were initially run at a 260km/h ceiling for a period after opening), it was possible to increase the maximum running speed to 300km/h but the nature of the original lime meant the tightness of certain curves only allowed the original 270km/h limit, I believe there are thus still four stretches where TGVs thus reduce to this speed on the line.

I assume these issues were partly in mind when designing the later LGVs and are partly in mind with HS2.

 

[Sorcerer]

It's mostly just standard futureproofing that all high-speed rail lines are given along with the trains. The Frecciarossa 1000 which the HS2 stock will be derived from is built to be capable of 400km/h (250mph) but never runs above the typical 300/320 mark.

Most high-speed lines have a higher design speed than service speed. The newer 320km/h LGV lines in France were built with a profile suitable for 350km/h.

There is an element of ensuring some future proofing.

The original French LGV, the Sud-Est from Paris to Lyon was originally 270km/h throughout (trains were initially run at a 260km/h ceiling for a period after opening), it was possible to increase the maximum running speed to 300km/h but the nature of the original lime meant the tightness of certain curves only allowed the original 270km/h limit, I believe there are thus still four stretches where TGVs thus reduce to this speed on the line.

I assume these issues were partly in mind when designing the later LGVs and are partly in mind with HS2.

What's more with French high speed rail is that the 430 in TVM430 is apparently the maximum capable speed that can be operated under the signalling system even though it will likely never happen due to engineering, cost and the lack of need for it in a country like France.

 

[hexagon789]

What's more with French high speed rail is that the 430 in TVM430 is apparently the maximum capable speed that can be operated under the signalling system even though it will likely never happen due to engineering, cost and the lack of need for it in a country like France.

Cheaper to replace the cab signalling equipment than upgrade the line though!

But I yes, I'm not sure 430km/h will ever be achieved in normal, regular passenger service. 350 could be, but I understand the significant increase in energy costs is the prime factor why the SNCF at least ruled out regular running at more than 320km/h. (The original AGV project was, I understand, to actually run at up to 360km/h in normal service, presumably held to 350 on suitable lines, as opposed to merely being capable of these higher speeds.)

 

[LNW-GW Joint]

The original French LGV, the Sud-Est from Paris to Lyon was originally 270km/h throughout (trains were initially run at a 260km/h ceiling for a period after opening), it was possible to increase the maximum running speed to 300km/h but the nature of the original lime meant the tightness of certain curves only allowed the original 270km/h limit, I believe there are thus still four stretches where TGVs thus reduce to this speed on the line.

The long-term speed limits on LGV-SE are I think limited by vertical curvature because of the steep hills in Bourgogne (max 3.6% or 1/28).
Like most other HS lines HS2 won't have gradients anything like as steep on its fast sections.

 

[hexagon789]

The long-term speed limits on LGV-SE are I think limited by vertical curvature because of the steep hills in Bourgogne (max 3.6% or 1/28).
Like most other HS lines HS2 won't have gradients anything like as steep on its fast sections.

Ah, I read curvature as horizontal, but I seem to recall vaguely reading about the severe rapid changes in gradient also affecting the running speeds on the line; something else I think was reduced on later lines with the hindsight that experience of the LGV Sud-Est afforded.

 

[Transilien]

Ahh okay, that makes sense. I thought the regular top speed was 360km/h it seemed to be implied on things like open railway map where usually the regular top speed is shown

 

[hexagon789]

Ahh okay, that makes sense. I thought the regular top speed was 360km/h it seemed to be implied on things like open railway map where usually the regular top speed is shown

360 design, i.e. the maximum the line profile allows with a 330km/h service ceiling.

Essentially 10km/h higher in each respect than the newer French LGVs.

 

[JamesT]

360 design, i.e. the maximum the line profile allows with a 330km/h service ceiling.

Essentially 10km/h higher in each respect than the newer French LGVs.

My understanding is the line profile is a maximum of 400kph, though many sections will not reach that speed (e.g. tunnels). The initial rolling stock order is for trains capable of 360kph, but normal scheduling will be for 330kph with the extra reserved for making up time.

 

[hexagon789]

My understanding is the line profile is a maximum of 400kph, though many sections will not reach that speed (e.g. tunnels). The initial rolling stock order is for trains capable of 360kph, but normal scheduling will be for 330kph with the extra reserved for making up time.

It keeps changing everytime I read a piece on the project. Sometimes it's 400 design, sometimes 360. Sometimes they say it has/had been downgraded from 400 to 360.

I see the source quoted on Wikipedia does say 400 design, 360 maximum in service, 330 routinely.

So presumably as mentioned upthread, that means trains would be timed initially based on maximum 330km/ running but could accelerate to 360km/h where permitted to recoup delays.

A bit like Southeastern High-Speed initially, being timed at 200km/h but allowed 225km/h running late; albeit now timed for normal 225km/h operation.

 

[Nottingham59]

In most places 300km/h is the standard top speed, so why is HS2 (being short in length for a high speed line) have a top speed of 360km/h?

Because it was grossly over-specified, like every other aspect of HS2.

 

[lachlan]

Because it was grossly over-specified, like every other aspect of HS2.

Or it was futureproofed, especially important if it was to be extended up to say Glasgow and Edinburgh. Depends on your outlook I suppose

 

[stuu]

Because it was grossly over-specified, like every other aspect of HS2.

No, the design speed for the open section north of the Chilterns was one of the most sensible choices. Deciding to rework the landscape for 200m each side of the railway to make sure no cow in Northamptonshire ever sees a train was a far stupider decision

 

[ABB125]

Alignment suitable for 400km/h*
Rail systems (track, signalling, trains) suitable for 360km/h
Trains timetabled for 330km/h, with scope to run at 360 if late

At least, that's my understanding...

*Not everywhere, obviously! All tunnels are limited to 360 or less, for aerodynamic reasons I believe, although in practice that'll make no difference. South of the Chiltern tunnel the speed starts to drop on the approach to London. "Branches" (ie: Birmingham spur) are 230km/h design speed until close to the termini.

 

[Nottingham59]

No, the design speed for the open section north of the Chilterns was one of the most sensible choices.

Maybe. Choosing an alignment that is straight enough, and digging tunnels wide enough, to eventually carry trains at 400kph makes some sense, but boasting about such high speeds at the start of the project just served to scare ppeople and strengthen public opposition in places along the route

(And I doubt very much if 400kph will ever happen. There's the S-bend just north of the Delta Junction (design speed 350kph), and too many green tunnels (380) and Long Inchington tunnel (360) to allow for sustained high speed running at 400kph, so it's unlikely ever to be economically worthwhile.)

Deciding to rework the landscape for 200m each side of the railway to make sure no cow in Northamptonshire ever sees a train was a far stupider decision

We can certainly agree on that. I wonder how much cost was incurred by the decision to replace a simple straightforward viaduct over the A38 and WCML at Lichfield with a deep cuttings and underbridges?

And, as you say, the same in Northamptonshire. And the Chilterns.

 

[Elecman]

I’m HS2s case political vanity

 

[YorkshireBear]

The Green Signals podcast interview with Andrew McNaughton is very enlightening on this subject and I would encourage anyone to listen. Link to youtube Link Here

In essence, the alignment was set on avoiding things they didn't want to hit and it just so happens that alignment can achieve that speed. Speak to any HS rail organisation from Europe as they say, build it for way more than your start point, otherwise you get like France with full lines running at capacity with demand suppressed. The government fully backed this decision making but now use it to criticise HS2.

Anyway happy listening for those who have t seen it.