The rule for single-unit (straight) vehicles (such as buses, three-axle trucks, and ambulances) on upgrades is the same as for cars: If there is a curb, turn your wheels away from the curb (i.e., toward the centre of the road). If your vehicle’s brakes fail, the curb will block your vehicle from rolling backward. If there is no curb, turn your wheels toward the edge of the road. If your vehicle’s brakes fail, your vehicle will roll off the road, not into traffic.