A heads-up display moves with your head; augmented reality moves with the world.

So, showing a billboard every 100m alongside the road showing your speed, heart rate, etc would be AR (and yes, a hud seems better option for this kind of thing)

Something like optimal trajectory or gamification of the surrounding environment

I don’t see how that’s possible, it would have a prerendered map for a path like a game? use laser sensors to warn you of danger? I think it’s very possible on unnatural roads but on off-road it would not be useful.

That’s still the definition of the technology. You’re right that it mostly doesn’t exist yet.

In unnatural places can have markers that tell it to show you things, like how cars auto park, invisible signals could do it too, they could add haptics and it would be AR.

When doing Strava segments, a ghost rider riding at your PR pace!

They had an issue with that at a military base!