Queuing was my experience. Holidaying in Spain, we visited Gibraltar for a day with our hire car.
Getting into Gibraltar from Spain wasn’t too bad, considering it is a physical border. But getting back to Spain again took hours as the Spanish were subjecting every single vehicle to a full and detailed search. When I asked why they were doing so, the border guard told me they were cracking down on tobacco smuggling.
That was a long time ago, 2005. Things may have improved, or got worse.
BTW we did find Gibraltar fascinating, and well worth the visit.