The New 3D Printing Thread

Would printing them vertically instead of horizontally be an option to reduce the supports?

Backing up Chris here the solution he came up with of slicing them as he did is probably the best solution.  If you printed them flat as one piece all the 'space' (aka where the wheels go etc) would require 'supporting infill' on the bottom of the piece.  This does not usually come away without leaving marks of some type and it would be a real balls ache of a job to sand them flat again to remove these marks.  Also if you have the lines to provide extra traction on those spaces these could get compromised by the supports.

Printing them on their sides which is what I suspect you mean by vertically would then require supports between the inner lips of the track pieces or else the top edge would not print correctly, also bear in mind these are curved pieces so the bottom edge would not sit flat on the print bed which again means supports to attach it to the bed while printing.  The other issue is the parts connecting with the bed would only have the footprint of the side on view of the track, this means you run the risk of the track leaning as it grows higher resulting in a poor quality print or in a worst case scenario a failure due to it leaning as there is no solid base for it to print from.

If you were talking a straight piece or single sided piece of track then it would be a different case as that would be a far easier print to achieve easily.