A four track railway runs through a common effectively splitting it into two except for a footbridge across the tracks. Should this be entered as a single common with a railway running through it or as two independent halves separated by the width of the railway?
I assume the railway is all fenced off, and the footbridge is the only way of crossing it?
If so, it sounds like the railway is not really part of the area of the common. So two separate areas of common on each side of the railway would be most accurate.
Does each part of the common have its own name, or do both parts just have the one name? If its just the one name, you might want to use a multipolygon relation, to show its 2 separate parts of the same common.