I was wondering, if there is any general rule, it should be in general wiki section.
I personally see good reason to have railroads crossing with junction and I already started discussion about railroads in Editing Experts forum. within this discussion there is one point regarding the junction on railroad crossings (following is my own opinion, which was disregarded by other Experts):
when railroad and normal road are crossing, we should take this junction in count for routing (penalty) and for traffic analysis (if there is slow traffic before the crossing, it doesn't mean real jam, but just train passing by and traffic is going back to normal after short time period.
also there are different avg. speed values before and after crossing so it makes sense to have the junction dividing the road segments.
so I tried to find any relevant rules on wiki, but haven't.