The guide on the 360 works more than well, but I'd also like to add my own two cents to this. During this mission, you'll get your first buggy, don't worry about running over anyone here; I don't think there's any applicable targets.
However, during the second vehicle section (after you open the checkpoint), you'll run into a series of Ceph troopers picking a fight with a CELL APC. Take out the APC, then get back on the buggy, and crush the Ceph. That'll be at least 3 targets.
Once you hit an area where you can't proceed w/the buggy (you'll know because there's an APC blocking the road), you'll be in the general area of the Archangel control tower. There's an APC in the area; find it, and run over a few folks with it. There's a lot of Ceph in the area, especially around the Air Defense Grid, so you should have a lot of opportunities to get it there (hell, you can probably get all of it here instead of getting them w/the buggy). That's how I got this achievement here. Don't worry about it being an APC and not a buggy; it's Crysis 3 (and I 1K'd the first back in the day); if I had to take a guess, it's registering crushes rather than vehicles.
Cheers folks.
Edit for clarity and spelling mistakes.