Ah, the old grate. Imagine a driveway with a fence running to each edge. ----||---- Now visualize a tubular gate that instead of sitting upright is lowered to the ground. Normally there is a few feet of space under the cattle gate. Farmers would pasture their cattle in these areas and the cattle would not step on the gate itself out of fear. Therefore, a normal gate did not have to be opened and closed each time the person used the driveway.
Dave