NASCAR uses a HANS (Head And Neck Something) device. It basically connects your helmet to your torso. It also protects the collar bone from the seat belts.

Why would a street bike helmet provide better protection than a dirt bike helmet?

I believe the wrist restraints UTVcrap is describing tie your wrists to your lap belt, so they work with a steering wheel.

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'08 Gen1 RZR, ITP's, Maxxis Bighorn 26-9-12's, Fireball 6" over suspension with Bilstien shocks & 14" of travel, GPS