# How do tracks limit the speed of a train?

I have heard that it is railway tracks, and not necessarily the locomotive and coach limitations, that usually limit speed in a particular section.

Of course the physical capabilities of the loco and coach present an absolute upper limit on speed, and this is understandable. I am trying to understand how the tracks limit speed so drastically. In the Indian Railways network, the newer locos and coaches can run at 160-180 kmph, but the tracks mostly limit them to 110 kmph, with some sectors supporting 130 kmph.

Setting side speed restrictions due to repair and maintenance, how do tracks limit the speed of a train?

If a train goes too fast through a curve, it can derail. That train was going around 180 km/h on a curve designed for 80 km/h.

One of the passenger trains I caught from time to time had a top speed of 160km/h (100mph). The train would make that speed generally where conditions allowed. However there was one section of rail where the sleepers were wooden as opposed to the more modern concrete. The driver once told me in that section, speed was limited to 130km/h based on the maximum load capacity of the older sleepers.

so at least in some areas, the support of the rails can be an issue, even if the rail and geometry of the track are not.

You might drive a too heavy vehicle over a road bridge FASTER rather than SLOWER.

But the bumps in the track… the train is sitting on very stiff suspension, and when it hits a bump… F=mA… due to stiffness of suspension.

You can’t have bouncy suspension … it would be like riding a pogo stick… (and cause leaning OUT of the corner, rather than into.)

Ah, I can tell you ,as I commuted by train for a few years, there was a section of track that was a. slow to pass through, and b, when you did, you often thought there was a collision,or at least the train staff could have warned about the bump… There was obviously some shifting of a bridge or something that was upsetting the track… it was at an area with lots of fill, I guess they just had to get piled inserted down to replace old floating bridge structures. IT doesn’t matter what the sleepers are made from if the entire track bed has shifted too much (it all shifts…)

It’s (mostly) the same issues as roads and cars really. You’re limited by the tightness of curves and the smoothness of the road/track.

Trains (and some trucks) are also speed-limited to reduce dynamic loads applied to bridges or other weakly supported tracks / roads.

See https://www.youtube.com/watch?v=JuP2ZDMh9I8 from about 1:15 to 2:15 for an example of grossly speed-limited track. There’s a few more snippets of nasty track in there too.

If a train gets too bouncy, it could derail, while a car’s wheels might just hop off the pavement for a split second. And the bounces probably get larger the faster you go.

That, I suspect is the big reason for speed limits outside of curves.

I take the train from Montreal to NYC regularly. The track is in dreadful condition and the speed is severely limited in some sections, sometimes to 20MPH. Then there was the time I took it in below 0F temperatures and they said they had to go slow because the track was brittle. On another occasion, temperature in the 90s, they said they had to go slow because the track was too soft. That service would be vastly improved by new track, but there is no money for that kind of infrastructure.

My wife and I once went coast-to-coast by rail, first class, in a sleeper. It was pretty exciting, but showed me that there is a lot of stuff you never would have imagined about the romantic long train trip.

We had left Chicago in the late afternoon, and were sleeping in our less-than-comfortable beds when I was awakened at 2am or so to a terrific shaking, as if we were riding over a washboard. It took an hour or so to get past that section.

It seems that there is a long section of bad track in Minnesota that we went over, and it likely will stay that way for years to come.

In the US at least, there are specific track classes, with defined limits.
Here is an article describing the various classes and limits.
As stated in previous posts, the condition of the track is determined by tie condition and spacing (keeping the track in gauge), the quality of the rails (including any defects), track hardware (tie-plates, clips, spikes, etc.), ballast & roadbed, and so on. ‘Excepted’ track is usually pretty poor, trains run very slow on it to limit the damage if (when in many cases) they derail (locomotives used to carry rerailersfor just such a situation, so the crew could right the errant piece of rolling stock and continue onward)

Wow! That’s a piece of hardware I never imagined existed. Cool!

Great post. As an exact reversal of this idea, i used to work in a facility that loaded 2,2KM trains (around 220 wagon pairs but 2 loco’s and compressor car) with iron ore. Every now and then, a little bit of iron would fall between carriages and sit on the rail. Once it built up to about knee height, a wagon pair proceeded to climb the little pile, and subsequently derailed himself right in our loading bay haha. Taking a couple of his comrade wagons with him.

So its amazing how little it takes to get these guys off the rails if it presents a slight abnormality to their gauge standard. These wagons has 110t of product each in them, and weighed another 30-40t of themselves!

hello,
i am new comer , the train speeds control at the curve and when any other train coming from another site to the next track.

Here’s some pretty awful track.