The Crew

This appears to only count in Freedrive mode. I was doing faction missions that were offroad until my Statistics counter got to 2000 miles. The trophy however did not unlock. Then I checked the Awards section and under "Freedrive > Professional > Rough Terrain" my counter was just over 50%. This meant it had only counted just over 1000 miles.

I tested running a faction mission and then checking the stats and it wouldn't count up. I guess since the award is under Freedrive, it has to be done in freedrive mode.

I combined this with going for 50 PVP games and getting 100 police pursuits. I would try to find a PVP match and drive cross country whilst I waited. I would stick near a road looking for the police to appear. Not very exciting, but it seemed to be the only way of doing it.