Okay, I know the OP said he did not plan to run double stack well cars but there may be others here who may. So I want to correct my earlier post about double stacks not clearing the superstructure cross bracing. My second test showed that the double stacks will clear the cross bracing. I am not sure why they didn't the first time. Anyway, the top cross bracing has diagonal members at each end and there is a very close clearance issue. Any rocking of the car from side to side can cause interference between the top container and the diagonal cross brace. I tested this using a Walthers well car and two containers making sure the approach to the bridge was perfectly level. The track was the standard track that comes with the bridge. Using other track with a different height (rail + ties) may affect the clearance issue.
