Where I live they only serve pedestrians, it was always like that, for years, because there's just no space, it's all a walking city. They are still packed with people each day, straight from 7 AM there are dozens of people ordering there.
avg drive through is like 6-10 cars before nobody can enter line, just keep that in mind when you see a lunch rush at a place where hundreds of people are in 5 min walking distance from work or home.