Exits 4 & 5 in one interchange. For a single interchange with ramps given different exit numbers, use the lower number.
Compare NY I-278 8 or CT CT15 57.
These US examples are examples where the rule applies, as they are one interchange with ramps given different numbers (
NY,
CT).
M4 8/9 isn't. M4 8/9 is a single interchange where all ramps are given the 'number' "8/9". (
here's it from the other direction to your below example).
I submit that this is somewhat similar to this.
I submit it really not similar at all:
1) the US example is multiple interchanges, not a single interchange like 8/9
2) there are UK examples of having multiple exits leave the mainline at a single point, and they use '&' (if more than one number is given), not '/'. cf
M20 J6&5,
M60 7&8.
8/9 is a
sui generis thing, rather than a labelling error. It would be more of an error to try and pretend its one of the scenarios you have posited and label as if that was the case when it isn't.
