This achievement requires you to travel 50 km in a row with a crew (2-4 players).
Very easy to do. Invite a friend into your crew and start in LA or Las Vegas. Set a marker in Miami and then switch to planes and fly 50km and you'll get your achievement. You can even rubber band your controller to avoid having to hold RT, just keep and eye on it and make sure your plane is levelled out. Took about 15-20 minutes, which is on the long side.
The achievement description says also says "drive", but you can be using any vehicle as me and the person I did it with started in planes, then switched to cars because we thought we had to drive cars, but the achievement unlocked after driving a car for 10-15km.