1) First step you should do one thing TURN IT OFF TOUCH DRIVE and go to manually with keyboard arrows keys RIGHT LEFT UP DOWN.
2) Second step PLAY this stage enter in career mode of the game is in Chapter 1 Season (Class D Rookie - Stage 6) can get me 10 cars/buses in one run, now aim for parked cars/buses. You will see a pop-up on the right side that says 'Traffic down' if you've done it right.
3) Third Step repeat this 5 times and you will achieve your goal knockdown 50 Traffic cars.