Strategy: So I found that the easiest way to get this is with the Koeningsegg on Red Light Runner. You start by taking out the first three cops. If you do it correctly, you should reach the sixth speedtrap around the same time you took down your third cop. When you reach it, or once you take down the third cop, turn around and race back as fast as you can. As soon as the fourth cop shows up, turn back again and go get him.
If you do this, you'll safely take down four cars in a single race. If you're skillful and/or lucky, you may take down a fifth and even a sixth one. My personal record here was six, at least.
Anyway, when you beat your fourth cop, you should still have time to safely reach the end of the race.
Vehicular Combat: To take down cops, Just race up to their sides and slam them. Slamming cop cars on the back does very little damage, but the T-bone on the side is sort of a weak spot. Depending on speed, I could even one-hit k.o. the cops some times.
Other tips:
- When you brake, cops brake too (it feels like you're braking their cars, actually). However, since your car is faster than theirs, you can easily catch up by braking a little, then letting your car go a little more.
- Don't forget that you still have to win the race for your takedowns to count. And to win, you must still pass some speed traps fast enough to score. That's why I suggest you go back after the third takedown instead of slowly crawling up to your opponents.
-I can confirm that the achievement unlocks once you finish the race, not when you reach your 100th takedown. Screenshot and everything.