I have no idea. It was added recently (https://www.openstreetmap.org/changeset/173912155) by a TomTom mapper. I think it would make more sense for it to be a single highway=motorway, but never got around to commenting that changeset for asking in Slack. Please go ahead and do that if you'd like.

I hope this isn't some routing hack for something that doesn't understand lane tagging...

Other random note is that the changeset I linked above has a #maproulette tag—I wonder if we could hunt down the challenge and figure out what it's trying to do.