If I were to speculate, I'd say that perhaps it might only be feasible in small & dense cities with low traffic, as such high frequency requires a lot of resources.
Was born in a small city with frequent public transportation (5-10 minutes for most routes). As I moved to larger & more congested cities, public transport became less convenient and the schedule more erratic.
Was born in a small city with frequent public transportation (5-10 minutes for most routes). As I moved to larger & more congested cities, public transport became less convenient and the schedule more erratic.