This is all a bit confusing, so I'll summarise briefly.

The number of lanes isn't based on access. And the number of lanes doesn't imply access. There are still 4 lanes here. When you say "isn't allowed" - that's not actually technically accurate. What you are saying is that regular vehicles (you and me in a car or on a bike) are not allowed on the tram tracks. After all, trams are allowed there - that's literally a designated tram lane. (Another example, an emergency vehicle can drive on the tram lanes.) In other words, the road is physically 4 lanes on the same level. For example, cars still have to cross the inner lanes when turning left, which have the embedded rails.

So what we really want to specify is that vehicles can only access outer lanes, which is done with per-lane access tagging: `vehicle:lanes:forward=no|yes` (and `vehicle:lanes:backward=no|yes`). This is the same principle like roads with lanes for public transport only ("A" marked lanes).

Now, I don't actually know which segments here have the restriction for this, so I don't want to map it yet. I will definitely survey this at some point though. If you know this is along the whole rebuilt road, we can add them now.