I think that a degree of common sense is required here.
If you are flying in 9999 visibility and you are following a motorway at a range of 7 miles, then it is possible that somebody else may be doing the same. The chances probably become higher, the closer you are to the feature.
Similiarly, as the visibility clamps in, the chances are that anybody following a line feature will be doing so from close in.
Similarly again, the bigger, more noteworthy and wider the line feature, the further away somebody can be, whilst still reasonably following the feature.
There will always be aircraft operating in complete ignorance of the line feature that you are following, and these aircraft will cross your route, and may be at your level.
The Rules of the Air are intended to make anybody following a line feature think about their position, and the collision risk that they might pose to others doing the same. That risk probably fades once you are more than 2 or 3 miles from the feature.
Any good?