Train Tracks Between The Tracks

[Nightcleaner]

I watch Lots of Train cab rides on you tube. Can anyone tell me What the inside Train tracks that you see on bridges and some bends are actually for?

The ones I mean always taper inwards at each end: Good example here of what i mean Media URL: https://youtu.be/NfGHKmGP75g
Description:

[Mamyalynne]

Try again.....

[EDDIE51]

They are an additional safety feature in case a train derails on a bridge,viaduct or dangerous bend.The train will not come fully off the rails as the second rail will hold it on the tracks.

[Buenchico]

They're known both as 'guard rails' and as 'check rails'.

https://www.quora.com/What-is-the-function-of-this-additional-rail-lines-inside-the-main-track

[mibn2cweus]

'Guard rails' are used extensively to insure trains stay on the chosen track when switching from one set of tracks to another.

https://en.wikipedia.org/wiki/Railroad_switch#Guard_rail_.28check_rail.29

[Peter Pedant]

didja never play with a frenz train set and see the how the bogeys travelled over points ? I spent hours fascinated by this. Put two points to gether and the bogey goes wibbly wobbly woo - and derails
loved doing that ( to someone else's trains )
and the guard rails prevent this from happening in the real world

on a straight rail a bogey will do simple harmonic motion - as the rails and the wheels dont fit exactly together
bit problem when they were designing the pendolino I recall
( but I am not a rail engineer )

[Peter Pedant]

here

https://en.wikipedia.org/wiki/Hunting_oscillation