If you run a siding or parallel tracks make sure you space it properly or you will have two trains collide, especially on curves. Also if you have a second level of track and you cross over another track make sure you have enough room to clear the train that passes underneath, engine and other tall pieces of rolling stock.
Steam engines have the cab roof that sticks out and the steps on either the tender or engine may hang out some(example an MTH T-1) and hit something like a bridge trestle.
Lee Fritz
