You need some combination of high-ridership and low-personnel-cost. You can get that in most of Europe and Asia, but incomes in North America are quite high and labour capture is high too. Most jurisdictions cannot afford the drivers necessary at high frequency because there isn’t enough density for it.
Skytrain bypasses this by not having drivers and perhaps as buses become AVs we could add many more of them here in the Bay Area with much higher frequency.
Skytrain bypasses this by not having drivers and perhaps as buses become AVs we could add many more of them here in the Bay Area with much higher frequency.