This achievement should be done after you acquire your first class x car from the campaign or from the auction house. You can work on it before, but its much easier later. Open the map and filter to Speed traps. Then go through as quickly as possible, using rewind to help yourself or taking the trap from the opposite direction.
When I completed this I had around 4 speed traps with 0 stars and the rest with 2 or 3 stars.
Edit: Thanks @Greedy136 for additional information:
They point out that you start out with a few speed traps, but will unlock more on the way to level 10. There are more than 20 speed traps in total. The game tells me, there are 28, but some are unlocked after reaching level 10, so obviously they cannot be used for this achievement. I only had 3 stars in 4 speed traps, when the achievement popped (most other traps had 2 stars). So if you get 2 stars but are too far from the 3 stars goal or simply do not like the track, just try the next speed trap.