In that case barrier=planter should be added to the planters (since they are placed to block the traffic). Even if it is legally allowed (i.e. there is no sign that forbids car traffic), there is no sane person who is going to drive there (since he would need to move two quite heavy planters or drive on the grassy area). The other problem is that all routers currently direct the traffic through these planters which is not quite right if you ask me (https://www.openstreetmap.org/directions?engine=graphhopper_car&route=42.68461%2C23.34832%3B42.68554%2C23.34966#map=18/42.68495/23.34962). I agree that it may have been a road at some point in the past but currently it is part of an area for a park (see plot 68134.108.217 on https://nag.sofia.bg/OpenMap/Zones).