Some folding bikes fit between the backs of seats. It's pretty great. https://1.bp.blogspot.com/-Fe7LjTABOkA/UlebTVDjtTI/AAAAAAAAcIw/H5nNafawqVw/s1600/trein+4+

Some folding bikes fit between the backs of seats. It's pretty great. https://1.bp.blogspot.com/-Fe7LjTABOkA/UlebTVDjtTI/AAAAAAAAcIw/H5nNafawqVw/s1600/trein+4+brompton.jpg https://1.bp.blogspot.com/-Fe7LjTABOkA/UlebTVDjtTI/AAAAAAAAc... If you can't view the image, visualize a train compartment with rows of seats with a shared table in between them. If there isn't a table, then the back of the seats are facing each other, and it's a perfect spot to fit a folding bike. Unfortunately, the bike has to be engineered for it. The more expensive Brompton fits, but my cheap one doesn't.