“One scenario they are looking at is people are forced to evacuate a heavily populated area then they will touch off car bombs in the backed up traffic”
A single blocked highway in the greater Philadelphia area jams all other area highways for hours on end, as motorists look for detours and clog other routes already slow at normal capacity. 6-10 people creating blockages simultaneously could immobilize the entire tri-state area.
Same in every city and when the traffic comes to a complete stop cars are only a few feet apart.
The hotter the fire gets the faster it spreads to the other cars.