Ok, I did this one last night, perfect ranking to perfect Insane difficulty.
It's actually quite easy...
Accelerate up the ramp and swing left (behind the lamppost) and drive straight into the nearest semi (it's blue), this causes all the vehicles to crash, you will get a crashbreaker, with this, blow yourself back to where you came from (the cars will already be past) and if you're lucky you'll catch the bus (I never), this will cause all these to crash (don't go to far), again, you'll crashbreaker it, blow yourself up and go back to where you first crashed and go over the pile, you should be able to catch the first car coming down that junction, hit that an all cars will pile into you, you should get ANOTHER crashbreaker, blow yourself up (again!) and hover over the new pile-up and the first pile-up to rank your points up. The Target car will crash into the 3rd crash you cause.