Cant you just steal a railway level crossing? Thoought of that but overhead cables prevent it.
Or make a rack and pinion like a folding garage door mounted sideways – Lack of clearance to the correct side of the gate
or a long bar that pops out the ground – Already mentioned the challenge of digging hols deep enough
Or a turntable with a crescent panel – Considered this using the rear wheel of the car to spin the round about but limited slip diff with stop that and the ground is on a slope.
All good suggestions but considered and rejected for the reasons above