They do use expansion joints they’re just a little more modern now. Look up “breather switch” for examples. Another common technique is to install the track already heated so it can’t get even larger and buckle.
Just curious: what's the benefit of installing them pre-heated vs installing them at air temperature with a slight expansion space between them? I assume that when they are installed pre-heated, the first thing they do is cool down and contract.
One reason why inductive breaking (Wirbelstrombremse) is only allowed on "feste Fahrbahn" (ballast less track) for Germany's high speed ICE (inter City express) trains, at least as a service brake.
On some ballasted track they're allowed for emergency breaking ("Schnellbremsung"), as they can interfere with equipment like axle counters.
This is done because they have to wait for the track to cool before they are able to safely drive on it after it got heated.
These are btw just a linear induction motor with the field coils locked to standstill.
I have since wondered about using this for traction, as it's likely not too efficient but ought to have potential for a much simpler drive train, using much longer parts of rail under the vehicle to get the desired force with a low slip (and thus low rail heating).
Say, for vehicles that don't normally need (this much) acceleration, and would thus prefer few/no driven axles.
We are at a point where power electronics are cheaper than some traditional transformer technology, and being able to deliver high accelerations (on the order of 3~6 m/s²) near zero speed to regional trains could vastly improve their average speed.
Just make the people have a wall/backrest and those forces are harmless.
Turn them around for the next stop if you want to brake that quickly or use it to catch up a small train car to a full trai;, have two stories, walkway backwards on top, forwards bottom, and drop the tail off from the through train after it has exchanged people.
Don't need seats there, just walls at, like, shoulder width pitch, to let people stand with their back in the right direction.
If only track pairs were more cleanly parallel, you could just have bridges and let people transfer to and from the fast through train using a local access facilitator train.
That in particular would also let you catch a connecting train without either of them slowing down (a lot) to provide this opportunity, which might even be the bigger benefit.
Sadly trains take ages to board lengthwise as European track clearance gauge doesn't allow for two proper unidirectional lanes of people traffic with decent cross section left for seating, so you'd have to spread the arrival/departure shuttles between front and back for a single dominant people traffic direction (from arrival seat to their transit seat and onwards to their departure seat).
I guess you could work around by using distinct small shuttles that maybe briefly combine for aerodynamics, in relative breaking distance w.r.t. service brakes, and respond to a switch that doesn't reach a safe locked end position by unfolding wave breaker barricades into the gangway (articulated so that they naturally support people leaning against them due to deceleration forces, so they get kinda pushed into place by people using them) and alerting passengers about the imminent rapid coordinated deceleration.
A couple seconds notice should suffice to let people move to hold onto their stuff that'd otherwise go flying from a G of deceleration.
Coming to a stop from 300km/h takes 2.3km (27.8s of travel) at 1.5m/s² (the AFAIK limit for normal standard train carriages to match how the passengers behave), but at 10m/s² it only takes 247m (4.2s of travel).
This would be the minimum dead space/time to stop safely in case a switch fails to transition. Regroup convoys between branching points a bit, and you could run at current-day capacity levels despite most carriages not stopping at any given station (the others just skip past as they didn't branch off).
Honestly I still wonder if suspension rail system Eugen-Langen isn't better for high speed people transport due to the severe passive tilt capability (+-15° in production for a century; +-30° tested (the production deployment wasn't authorized to anywhere near it's tilt angle speed limit for many years, and the frequent stops/stations didn't make that angle look restrictive for the technology at the time: the track isn't even banked as far as I know!)), especially because you don't typically want to share track between high speed people transport and generic mainline rail traffic.
Not needing the extensive tunneling/wide-span bridging ought to make the track suspension requirement worthwhile...
Particularly with how cheap we can make steel truss sections in automated factories, and e.g. sling it under the track for transport to installation site.
Drop it for the irregular junction areas, and just put cheap normal rail to wheel the segments across the junction.
Roller coaster technology has made the needed fast track switches a proven technology, too. (It's really similar to a suspension rollercoaster just with motors and an electric "3rd" rail.)
I for one can't wait for full ETCS Level 3 to become a thing used in production.
They do (sometimes) preheat continuous welded rail during installation to prevent buckling. The temperature used will vary based on the local environment (Minnesota will use a lower destressing temperature than Florida). Shorter sections of track (like in a switching yard) may not be destressed at all because there isn't enough length to cause a buckle.
> Compressive forces result from stresses induced in a constrained rail by temperature above its "stress free" state, and from mechanical sources such as braking, rolling friction and wheel flanging on curves. The temperature of the rail at the "stress-free" state is known as the rail neutral temperature (i.e. the temperature at which the rail experiences zero longitudinal force). Initially, the rail's installation temperature or "anchoring temperature" is the rail's neutral temperature. Hence, at rail temperatures above the neutral, compressive forces are generated, and at temperatures below the neutral, tensile forces are developed. Track maintenance practices address the high thermal load problem by anchoring the rail at (neutral) temperature of 95 -110 F. This high neutral temperature range prevents the generation of excessively high buckling forces even when the rail temperatures reach 130 -150 F.
Some railroads that experience wide summer vs. winter temperature differences may choose to install expansion joints. Like most things, there are trade-offs, like increased maintenance costs and increased chance of derailment at the joint.
Welded rail buckling in hot weather has become a real issue with global warming and wider temperature swings.[1][2] Australia has especially bad problems, due to wide temperature swings and very long runs of straight track.
When I was in London in the early 2000's, the Central Line was closed because of the heat damaging the tracks (they never used the word buckle in their announcement, but that was probably what happened). If they have a track problem that far under ground, it's a serious heat wave.
> If they have a track problem that far under ground, it's a serious heat wave.
Unintuitively, parts of the London underground are notorious for being extremely hot. Especially the central line is super hot due to the material the tunnels are dug into being an extremely good insulator/heat store.
It's also that they don't cool the tunnels like they really really ought to (just feed frozen water into the tunnels and drag the meltwater back out if it won't drain by itself, say by fitting some cars with slush sprayers like how manure is sprayed from the back of a tanker on agricultural fields, or dropping ice cubes spread-about).
Use ice-based AC for the passengers, not heat pumps dumping into the tunnels.
Change the breaking resistors to not be on the train, but the rectifier stations, and make them vent outside. Or change them to dump heat into what's a big insulated kettle that gets filled with ice or at least disposes the resulting hot water outside, not hot air into the tunnels.
