I purchased the book, How to Build Model Railroad Benchwork by Lynn Westcott and on page 9 he didn't answer my question. He said, " ---spacing between tracks in critical. If you don't have data to guide you here, try your longest cars and locomotives by placing them upon your plan to be sure they don't sideswipe on parallel routes and curves". Let's assume I don't have any cars or locomotives. A model railroader was selling his passenger cars on eBay because they were too long and wouldn't work on his layout. I don't want to be like that fellow in the future. I would like to be confident that I have planned ahead. I would appreciate any data on this subject from your school of hard knocks.