realistically how fast could trains get?

[popeter45]

simple question, 320km/h is the current "high speed" spec on new lines but stuff like HS2 and some lines in China are being built for 360km/h and some trains designed for up to 400km/h and test runs reaching far above that

as i dont think supersonic trains are gonna be a thing, whats prob the realistic could we see actual passenger trains reaching in the next 50 or so years?

 

[MattRat]

I definitely see 400km/h becoming the new standard for conventional trains. The technology has already been shown as capable, and all that's left is mass production.

As for beyond that, the fastest conventional train is 575km/h, but as that was only a test environment and a small train, you'd most likely have to knock that back to 500km/h in passenger service, unless a breakthrough is made.

However, if talking Maglev, due to only having to deal with air resistance, it would work more like a plane. Now, commercial jets operate at around mach 0.85, although this is at 30k feet, so the speed of sound is actually slower. What this means is that at lower altitude, like sea level where trains roughly operate, mach 0.85 would actually be faster, ultimately leading to a figure of around 1,000km/h theoretically without having to deal with any of the effects of being near or at or above the speed of sound, but again, that's just theoretical at this point.

 

[SynthD]

What are your parameters? China and Japan have the distances and investment/demand to go >500km/h. HS2 is, or was, designed in some ways for 400, but will only reach 320 in the next 50 years. Europe will do slightly better than that.

 

[Sonik]

When talking about speed, I think it's important to distinguish between technical and economic viability, the classic example being Concord vs Subsonic Jets.

Edge technology is of course possible, but by definition, economics will always dominate in mass transit. Concord held on for a while but a premium model such as this doesn't work on the railway, because infrastructure costs dominate by an order of magnitude, and speed differentials eat capacity. So you need high demand at the required price level, to make any dedicated infrastructure viable.

Decarbonisation also changes the economics of energy production, so if anything the optimum balance between speed and energy cost has already been reached. Maglev/hyperloop etc. do not solve this problem.

Therefore IMO we are unlikely to see widespread adoption of much higher speed systems until energy can be produced vastly cheaper. Renewables can do this but not consistently, so the conundrum is lowering the cost of energy storage.

 

[mike57]

Assuming conventional rail:

There must be a physical limits,

• When the friction at rail wheel interface is the same as the air resistance, try to put any more power in to go any faster and you will get wheel slip rather than an increase in speed
• Air friction on the outer skin causing heating problems

Also practical limits

• Maximum power that can be delivered by overhead catenary
• Largest motors that can be accomodated
• Braking systems
• Overall energy consumption

I am not sure how close to any of these limits the current 575km/hr record set by a TGV was, but my feeling is it was getting close to the pratical limits, you may have been able squeeze a little bit more out, but given current technology I reckon 500km/hr would be unlikely to be exceeded by service trains.

Geographically only the largest countries would be able to really benefit from these increased speeds, and of those countries only China has embraced high speed rail. It would be interesting to ask this question of an engineer leading Chinese railway developments, as I suspect they have a pretty good answer to all these questions.

Once you deal with the engineering and physical limitations you then get to the driving force: cost. Given the current situation I suspect that at 300-400km/hr we are at the top end of what is supportable from an economic point of view, including energy cost. Given the nature of railways it would be far more difficult to thread one 'Ultra Speed' train through current rail systems, even if fares charged reflected the extra costs, unlike a Concord Mk2 which would be a easier proposition.

 

[stuu]

As well as the other factors already mentioned, the biggest issues are:
Heat in the electrical/mechanical systems, especially wheel bearings
Rayleigh waves in the formation

400 km/h is pretty much the absolute limit for wheels on rails, until advances in material science overcome those issues. And even then, maglevs are probably easier

 

[Trainbike46]

In practice, the ability to find a suitable alignment may also be a limit. The faster you want to go, the straighter you alignment needs to be, and in many places finding a suitable alignment may present problems, so that is another limiting factor on speed

 

[Sonik]

I am not sure how close to any of these limits the current 575km/hr record set by a TGV was, but my feeling is it was getting close to the pratical limits, you may have been able squeeze a little bit more out, but given current technology I reckon 500km/hr would be unlikely to be exceeded by service trains.

IIRC for the TGV record, the OLE line voltage was increased, the train specially modified and the line completely cleared for the run, allowing the full section power available to be used by just the one train.

A regular service at such speeds would therefore, as a minimum, necessitate very costly upgrades to the OLE and power feeds, unlikely to be viable just for the available time saving. It has been possible over the last decade to increase speeds over unit energy cost by e.g. lighter build, improved aerodynamics and higher seating density, but these are all one-time gains.

So I think it's most likely the highest speed services won't get much faster, but regular regional and commuter services will continue to catch up where incremental upgrades are possible. For commuter services in particular, the high density of usage helps justify the investment.

 

[Irascible]

In practice, the ability to find a suitable alignment may also be a limit. The faster you want to go, the straighter you alignment needs to be, and in many places finding a suitable alignment may present problems, so that is another limiting factor on speed

Maintenance starts getting ridiculous also.

There are reports on practical ( both economic and operational ) speed limits for european HSR around - I don't remember exactly where, but I think some searching of discussions about european maglev ( was it UK Ultraspeed here? ) should pick something up. I vaguely remember there's no real point going above 350-400kph right now. Changes in the aviation industry might impact that, though.

Personally I think we shouldn't keep pushing, especially if we're keen on lambasting the airline industry for emissions. 350kph is still considerably faster than driving.

 

[HSTEd]

Well we have to define a "train" in order to answer this question.

Service "trains" have already reached 430km/h on the Shanghai Airport Maglev, and the Chūō Shinkansen will reach 505km/h.
For steel wheel on steel rail? I doubt we will see much more than 350km/h in extended operational service.

 

[Snow1964]

I think although 400km/h+ is technically possible

Commercially the cost of going above 320-330km/h (about 199-205mph) doesn’t usually make any sense. Higher power requirements and more maintenance would be required, and in most cases only save few extra minutes which doesn’t bring in sufficient extra revenue for the extra costs.

I think France, Italy, Spain and Germany have all come to same conclusion regarding 320-330km/h

 

[Peter Mugridge]

IIRC for the TGV record, the OLE line voltage was increased, the train specially modified and the line completely cleared for the run, allowing the full section power available to be used by just the one train.

It was also a test for the purposes of checking aerodynamics, the wheel / rail performance and the pantograph / wire performance.

 

[SynthD]

It was also a test for the purposes of checking aerodynamics, the wheel / rail performance and the pantograph / wire performance.

What was learned on those topics?

 

[Peter Mugridge]

What was learned on those topics?

From memory, they were looking to see how stable the various interfaces were at super high speeds and what the performance risks were at what speeds - all with a view to future development of high speed rail. The results should be available online somewhere; it's so long since i read about it that I won't trust my memory in repeating what I remember but that there were interesting results in some of them.

 

[miklcct]

Commercially the cost of going above 320-330km/h (about 199-205mph) doesn’t usually make any sense. Higher power requirements and more maintenance would be required, and in most cases only save few extra minutes which doesn’t bring in sufficient extra revenue for the extra costs.

For flows such as Beijing - Shanghai or Beijing - Guangzhou, such speed increases can be worthwhile.

 

[LYuen]

For EMU sets, Japanese purpose built experimental units to achieve 443 and 425 kph (275 and 264mph) while modified revenue unit achieve 362 km/h (225 mph).
In China, unmodified revenue unit also achieved 485kph/300mph
Standard gauge track does physically allow speed up to 500kph given good rail alignment, so the speed is restricted for other limits.
On the rolling stock side,

• Motor power output
• Car body strength
• Component strength, e.g. pantograph.
• Braking system heating

And on the regulation side, which significantly impact the design of Shinkansen,

• Noise produced at the maximum speed
• Braking distance (A major thing for Japan because of earthquakes. A train running at its maximum speed must completely stop within 4km. Though this was in fact easier to beat than the noise restriction)

However, the defining factor of track/rolling stock speed time of journey and service pattern.
JR East is now experimenting 360kph from 320kph operational because that will put the journey time between Tokyo and Sapporo just under 4 hours, making it a meaningful option to flying.
China operates the Beijing Shanghai high speed line at 350kph so that the journey time between the 2 cities is just over 4 hours.

In the case of Europe or UK, the distance between metropolitan cities is surprisingly short. WCML and ECML link North England cities to London in 2-3 hours, which has already make trains competitive. While for Scotland, the proposed HS2 track speed will also reduce journey time to around 4 hours (can be more if track improvement is happening in Scotland).

 

[HSTEd]

• Braking distance (A major thing for Japan because of earthquakes. A train running at its maximum speed must completely stop within 4km. Though this was in fact easier to beat than the noise restriction)

I think its worth noting that at least one test set on the Shinkansen was fitted with air brakes to allow it to decelerate more rapidly.

 

[LYuen]

I think its worth noting that at least one test set on the Shinkansen was fitted with air brakes to allow it to decelerate more rapidly.

Yes, in fact those spoiler brakes were fitted to all recent prototypes.
However, when production models were derived from prototypes, they were no longer needed because the top speed was reduced.

 

[Cloud Strife]

Personally I think we shouldn't keep pushing, especially if we're keen on lambasting the airline industry for emissions. 350kph is still considerably faster than driving.

I think it does depend on the route. Barcelona-Madrid for instance is a good candidate for 400km/h, because it would finally kill off flights on that route and bring the journey time to under 2 hours.

 

[SynthD]

Personally I think we shouldn't keep pushing, especially if we're keen on lambasting the airline industry for emissions. 350kph is still considerably faster than driving.

Air resistance is the square of speed. Travelling at 900kph (airline speeds) have five times the resistance (and resulting emissions) of 400kph.

 

[D854_Tiger]

Air resistance is the square of speed. Travelling at 900kph (airline speeds) have five times the resistance (and resulting emissions) of 400kph.

The French claim air resistance is the greatest obstacle to making their TGVs go faster.

The train, track and overhead could do it but the energy costs start going through the roof much above 320 kph.

Then energy cost is something of a problem in Europe at the moment.

 

[Route115?]

Thats why there are suggestions of running trains in vacuum tubes. Its not technically simple though.

 

[MattRat]

Thats why there are suggestions of running trains in vacuum tubes. Its not technically simple though.

Not really a suggestion when it would be more costly to create said vacuum than to run trains faster through the air.

 

[HSTEd]

You can also fit giant Shinkansen style noses to trains to try and reduce drag - although that is mostly about reducing pressure waves in the smaller Japanese tunnels.

 

[507020]

IIRC for the TGV record, the OLE line voltage was increased, the train specially modified and the line completely cleared for the run, allowing the full section power available to be used by just the one train.

The line was also brand new and the record attempt was made before the start of the passenger service, so there was no disruption. Rather passengers were able to travel on the fastest railway in the world after the record was set.

 

[mike57]

Air resistance is the square of speed. Travelling at 900kph (airline speeds) have five times the resistance (and resulting emissions) of 400kph.

Doesn't the fact that air pressure is higher at sea level also come into the equation, as you have to displace more air at sea level than at 30,000ft

 

[Irascible]

Doesn't the fact that air pressure is higher at sea level also come into the equation, as you have to displace more air at sea level than at 30,000ft

Air density changes with altitude make a *significant* difference, yes. However what's also significant is the vast amount of energy you spend getting an airliner up there, which you can't get back again...