I have taken your advise and increased the wall count to 4, its what I normally use on my train tracks. I must have made a mistake on the print profile. Thanks for pointing it out. I'm sorry you had one break. I normally test the prints out with my son, who is pretty rough. Once they don't break for him, I then release them.

Thanks. It's not the first train model my child has broken, and it certainly won't be the last :)

Thanks for the feedback, I am considering a longer one. The reason for the short one is that multiple can be combined to form a long tunnel and the print time is roughly the same. However because the tunnel is closed, a long tunnel can end up with a train stuck inside without little hands being able to reach it if it stops directly in the middle. I also had created a standalone liftable tunnel set that included longer tunnels, however they were and I simply took it down.