If you try to solve all the puzzles yourself, then you should have no problem getting this, and the 50 collisions, achievement.
However, if you follow a level Guide, you more than likely will need to grind out 100s of collisions to get the achievements.
It is worth noting that "Cars Hit" DOES NOT mean "Collisions". A car hitting another car counts as 2 cars hit but is only 1 collision. My solution will get you 4 collisions every 7 seconds or so, so grinding this out won't take long if you use my level solutions.
First, use the video below and follow the setup for Level 30 at (50:39).
Then, fast-forward to (55:03) and move the yellow taxi all the way forward. Now you can run the simulation over and over to grind out your final collisions!
If you have any questions, feel free to ask!