A bus every 4 minutes is still generally cheaper (and lower capacity) than a tram or high frequency commuter rail.
For instance, here there are a couple of bus routes which do every 6 minutes or so at peak times; each bus takes 80 people. However, the tram lines run every 4 minutes at peak times; each tram takes 360 people.
For instance, here there are a couple of bus routes which do every 6 minutes or so at peak times; each bus takes 80 people. However, the tram lines run every 4 minutes at peak times; each tram takes 360 people.