To unlock these tracks, complete certain tasks.

Track	Task
Buggy Basement	Unlock Every Buggy.
Buggy Beach	Get All Gold Medal On Pub 1 In Challenge 1 Mode.
Buggy Nights	Get All Gold Medal On Pub 3 In Challenge 1 Mode.
Claw Shore	Get All Gold Medal On Pub 2 In Challenge 1 Mode.
Creepy Copse	Get All Gold Medal On Pub 2 In Challenge 1 Mode.
Frosty's Park	Get All Gold Medal On Pub 3 In Challenge 1 Mode.
Mountain Retreat	Get All Gold Medal On Pub 2 In Challenge 1 Mode.
Muddy Slipway	Get All Gold Medal On Pub 1 In Challenge 1 Mode.
Night Falls	Complete Challenge 1 Mode.
Run Down Town	Complete Challenge 1 Mode.
The Catacombs	Get All Gold Medal On Pub 3 In Challenge 1 Mode.
Up 'N' Dune	Get All Gold Medal On Pub 3 In Challenge 1 Mode.
Velocicano	Get All Gold Medal On Pub 1 In Challenge 1 Mode.
Way Of The Buggy	Complete Challenge 1 Mode.