What are the "inner rails"?

[SelflessPotato]

Hello!

Watching railfan window views, you can often see some sort of "inner rails" or something between the rails that cars actually run on. I know that there are often just old rails that have been replaced which get left between the replacement rails, but what I'm talking about don't seem like that, these seem more intentional. Here's an example of what I'm referring to:

In that image, you can see the "inner rails" which seem to be pretty consistently present, and the yellow paint on the ends makes it seem like they are there for a reason. Assuming they serve a purpose, what purpose are they there for?

Thanks!

[SevenEleven]

If I remember correctly, the inner rails are to help a top the train from going over the tracks completely, should it derail. 

[SelflessPotato]

Ah okay, that would definitely make sense - I do seem to notice them most often (if not solely) on elevated tracks. Thanks for the response!!