Most of the Marvel characters wouldn't be hurt by a car. Now in the world of Heroscape that might be a viable game variation; however, I just don't see the Marvel characters getting crushed, or even hurt.
Now if you were gonna play it with Heroscape the I would suggest not using the d20 roll method. What I would do is the following:
Have some cars on the map. Keep them lets say 2 spaces apart. Now at the end of every round move the cars foward 1 space. Any character hit by the car recieves 1 wound. Froggerscape
I just don't like the instant death roll. Also this way would require more strategy. For example if your road is 4 hexex wide then most characters would require 2 order markers to move across it. Then you have to deal with unprotected units in enemy terrority.
I would also scrap the park scenario. I would have the road dividing the various teams. Mabye use the RTTFF bridge to simulating one of those high crossing things over the innerstate. The road and cars would be used as a tatical dividing point.
All in all very good ideas. I hope I am not being too critical of your thoughts, this is just how I would perfer to play. I think I am gonna build a map on virturial scape and see how it looks.