Of course you can. Just design the area for walking and biking and let the motor vehicle traffic flow around that.
A car driver is not nearly as inconvenienced by an incline as a pedestrian or cyclist would be. If we don't want to do more in depth changes, then at least we could just let motor vehicle traffic tunnel under or bridge over foot and bicycle paths instead of the other way around.
Tunnels and bridges are expensive. If there's a choice between a pedestrian bridge and a car bridge, the pedestrian bridge will be less expensive. And vastly more people drive than walk. It's pretty obvious how we end up with the infrasructure we have.
A car driver is not nearly as inconvenienced by an incline as a pedestrian or cyclist would be. If we don't want to do more in depth changes, then at least we could just let motor vehicle traffic tunnel under or bridge over foot and bicycle paths instead of the other way around.