You start with a basic slow truck, and as you progress quicker more agile trucks are unlocked. To reach the next truck certain points have to be reached, and it gets harder and harder to achieve the scores needed. The faster you go the more dangerous the winding roads become. Finding proper shortcuts that gets you, and your parcels to the destination is key. Big jumps can be good if you manage to hit them spot on for a landing straight into the green delivery zone.