Gibraltar is joined to Spain by a flat strip of sand, and during the Second World War the runway was laid straight across it, because that was the only flat ground there was. Which meant the main road into Gibraltar ran across the runway. For about eighty years, when a plane was due, barriers came down like a level crossing and the traffic waited while an airliner went past where the cars had just been. In March 2023 a road tunnel, about 350 metres long, opened under the end of the runway, and the cars stopped crossing. People on foot and on bicycles still do. So if you walk in from the border, you can still be asked to stand at a barrier and wait while somebody else arrives.