For what it's worth, in your picture the piece you highlighted is actually the surface the drive wheel that @CrashCoaster refers to makes contact with in order to get the train round the layout. In that picture, it's actually that small rail underneath the track that is carrying the power.It’s simply that an electrical current is used to power the trains; if you look at the track on this coaster, there’s a grey rail running on top of the normal coaster track (circled in yellow here). An electrical current is run through this rail to power the coaster wheels and also to brake them. There’s an assembly underneath the coaster cars that maintains a consistent connection to this gray rail, not too dissimilar from the way a subway works (subways have a third rail that is electrified; if you remember the show Mythbusters they tested the myth that you could be electrocuted from peeing on the third rail of a subway )
This is a decent picture:
The four greenish strips you see to the left are the busbars for the power, and the flat strip on the right is for the drive wheel.
EDIT: Fixed my left/right. Whoops.
You can see the drive wheel in this shot, but they're often not that easy to spot as there is lots of 'train' in the way.
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