The gas station they pushed the car into was built from scratch on a vacant lot, it was blown up for some footage that didn't make the movie. Also the motel where Twiggy was waiting for Elwood to show up was about a mile from the gas station.
This was near the town of West Chicago, Ill. where I lived at the time. When the town found out about what the building was for they required the movie company to be liable for any damage that might occur, good thing because when they blew up the gas station some nearby houses had some windows blown out.
One of my favorite movies too, I watched it about a month after I first moved to Mich. and it made me homesick for Chicago, didn't watch it again for a while after that.