The price of success?

A friend of mine attempted to attend a model train show at the first-ever exposition at the "Greater Philadelphia Expo Center" at Oaks, PA just north of King of Prussia off route 422. This show was HEAVILY promoted in the Philadelphia and Allentown areas. After sitting in traffic for over an hour, my friend decided to forget about the show, and tried to pass the exit in the left lane - which took him another half hour. He told me that posts by others in model train forums said that all streets in the area were completely gridlocked.

The first thing I though of is what would happen if a promoter would schedule a similar show in downtown Lancaster, and promote it heavily in surrounding areas. Could Lancaster's streets handle the traffic? Or, would the same thing happen here as did at Oaks?