It seems like it is not possible for one to create a short bridge with a single span (I.E. no pillars between the abutments). See these two pictures for a better explanation as to what I mean:
I tried to build this short railway bridge over a road but get a bridge pillar collision error even though a bridge that short should not need any pillars:
However if I then make the cutting through the embankment wider, it lets me build the bridge as it can now build a pillar, even though the span between the abutment and the pillar is wider than the single span in the first picture.
I consider this a bug as it should be possible to build bridges like in the first picture. There are thousands of bridges like that which span between two abutments without pillars in the middle.