Need for Speed

The hardest part about completing the Outlaw campaign and challenges is finding the police. You can drive around town for lengthy periods at time without running into the cops. There is one area at the South Port that always has a cop that you can find. Link down below that shows you where to find them.

Once you get rank 2 i believe, then you'll start seeing road blocks down some roads. The ones needed for this achievement are easy to break through, but you need to in the city and go down side streets in order to find them in my experience. They don't appear on the freeway from what i've seen.

In the slim chance there is no cop when you arrive, just leave the area for a few mins and come back. It's possible the cop was chasing someone else, but it will respawn shortly. Here is a video that shows you exactly where it's at.

During the game you'll get texts from "The Outlaw", goading you into taunting the police in various ways before he'll give you races (like all the other characters) like evade a $2500 ticket. After about 3 of these the task to smash 2 roadblocks will finally appear.

Normal 'sawhorse' type roadblocks will spawn when you're at a 2 star wanted level. However, their spawn rate seems to be intentionally lowered while this challenge is active. (I smashed about 5 in one evasion sequence while doing a ticket challenge earlier) When 3 stars are reached real roadblocks - cement barricades and police vans cutting off the entire street - start spawning, and the smash-able ones spawn even less. It's much more annoying than difficult. Just find a nice area with narrow streets and string the cops along until you have smashed thru 2, then make your getaway. The achievement will not pop until after your wanted level has cooled off completely.

[I noticed after hitting 4 stars, on some 6-10 lane roads a 3rd type of roadblock would spawn, with the vans and concrete, but there would be an opening on each side so you could zigzag thru. I do not know if these count, as I already had my 2 smashes/evasions/whathaveyou]