At that point, you can do things like pedestrian bridges, over/underpasses with roads and streets, or level crossings with signals. Instead of trying to mix traffic everywhere, have the two systems meet at certain well designed controlled spots. Instead of bikers being in a near constant state of “I am in traffic”, have certain points along their journey be “I am crossing a road.” These areas will almost certainly drive both cars and bikes to stop, and then one or the other gets to go at a time, rather than both are in motion failing to predict the other’s movements.