In the beginning you will get this with pure luck or it seems like an impossible task. At least it was for me. But after I beat the game and got the Trashmaster with the elite skin, this task became easy on almost every Road Trip. Only use your crashbreaker if necessary. Wait for the cars to pile up and look out for the yellow arrow marks to know where the next cars will appear. Always focus on cars with a turn signal. They are the hardest to catch.
But as with the rest of the game, practice makes perfect. Play the game and with time you will better understand the mechanics.