They actually dropped a real Ford Pinto from a helicopter for this.
The drop zone was an dockside area that the city used during the winter to store salt for de-icing streets.
A clear area, but practically in the middle of the city, which made for a nice view of the Chicago skyline during the drop.
In order to get permission for the drop, the production company had to prove the un-airworthyness of a Ford Pinto; to make sure it would really drop straight down, and not develop lift1) and veer off to crash somewhere in the city.
1) QV: Lifting Body concept
