Extra-long or double-decker buses have crush load capacities around 120 pax. A single Bart trainset can have a crush load capacity of about 2000 pax and can de

Extra-long or double-decker buses have crush load capacities around 120 pax. A single Bart trainset can have a crush load capacity of about 2000 pax and can depart every 2 minutes. So you would need a double decker bus departing roughly every 7.2 seconds to match that peak throughput. It just doesn't scale.