Runway length is not an issue. Maybe 20 years ago it was, but airlines can run 400+ pax flights out of SAN on several modern aircraft - 777s, 787s, 350s, etc, and even some older ones (767, 330, 340.) SAN can accommodate any aircraft except the A380, which honestly no airline would fly there even if they could.
24 operations: Gatwick has restrictions on operation from 23:00 until 6:00, much like SAN. According to Gatwick's website, they had 280,000 aircraft movements in 2016. Only 14,000 of those (5%) depart/arrive between 23:00 and 6:00. I can't find exact data, but my personal experience with Gatwick is that those night flights are often cargo. I just looked at overnight traffic for the last two days, and even during busy summer season, there were.... zero passenger departures during those hours. I can see only one landing from yesterday from Cuba at 5:15, which would be allowed at SAN as well. The fact is, if we assume half of all movements are landings (they better be
), then at
minimum, 97.5% of Gatwick's passengers fly during normal SAN operating hours.
SAN can grow to Gatwick levels of pax on a single runway, which represents 2-3 decades of projected use, simply by replacing 30 seat aircraft with 300 seat aircraft. And that will happen, when demand is there. And that's without considering other factors. High speed rail and autonomous ground transport will probably decrease airport utilization, and new air traffic control systems will increase the frequency of aircraft movements, increasing the number of aircraft that each runway can handle:
Combining all of these factors, its easy to see why the billion dollars investment in SAN was made: the location will have adequate capacity well into the future.