First a hint on getting to the final wave in a fast sweaty manner without destroying the roads.
If you position yourself on the crosswalk in line with any of the central gridlines, there is a sweet spot where the cars will miss you as you squeeze between them. The collision detection is not amazing here apart from the rollers and ambulance who can 1 hit kill you in this mode.
What I did was just find a sweet spot and avoid all cars until the final wave so that all roads were clear, then on the final wave I did the following:
Plant the marker in the central lane and blow up the white car. This will create a 6 grid tile, only use this to blow up the two back cars.
Then blow up the central first black car, to bring the red car forward one tile. Blow up the central red car. This will leave one bus on either side to destroy. Done right you should be -1 move for the 500pt bonus.
If you mess up on the final wave you can restart the current wave from the menu.