That hits the nail on its head: traffic systems in most modern countries have evolved to cater for two users only: cars on dedicated roads and pedestrians on the pavement, if at all. Bicycles are tolerated on the former, and at times on the latter. With more single track vehicles such as bicycles and scooters running at moderate speed, there is no provision for them in the road network. Hence the issue and its solution by creating drivable paths for them without conflicting or interfering with the incumbent users.