Busways in the Netherlands are mostly mapped based on the signage like sign F13:
This is inline with other types of highway classifications that have a sign accompanying them like cycleways, living streets and trunk roads.
There are situations where a road without a specific sign would be classified as highway=service.
However because one of these indicating signs is present the service road gets classified as the specific type.
A while back we had the same situation with service roads that also are living streets. This kind of double possibilities leads to situations where mappers can’t agree on a classification.
With living streets the solution was to add living_street=yes to the service road. A similar solution could be implemented here with highway=service+busway=yes.
However I am starting to think that highway=service is flawed. And that it might be a better solution to come up with a subtab to specify the type of road hierarchy/access type.