This only works on co-op, first you need to go to the second bus stop which is the diner.

So you're gunna want to go inside the diner. Player one must stand by the first door and player two must stand by the second door.

Both of you must open the doors at the same time to get inside, then you will see zombies bump into an invisible barrier or wall.

Then you can just shoot them, but you'll still have to shoot the zombies that come out of those two barriers inside.