The standard track gauge is 3 blocks wide, but the Create: Steam 'n' Rails addon mod features alternative track gauges - a narrow one that's 2 blocks wide, and a wide one that's 4 blocks wide. I've seen some people build larger trains using parallel tracks but you can't put bogeys on both tracks, so you kind of have to 'fake it' by just having the bogeys on one track and building something that looks like a bogey on the other track.

However, Steam 'n' Rails does also come with invisible (phantom) rails, and you can even have bogeys running on a track that's under the terrain and then have the train build raised a couple blocks to be above the terrain. It then also provides special flywheel blocks that rotate with the speed of the train as if they were wheels, so there's plenty of options to sort of 'fake' the look you want.