Even cities with decent public transport networks (such as Prague) tend to have a problem with tangential relations. Most lines go from some periphery to the center and to another periphery. If you need to travel between two peripheries, you have to be somewhat lucky to have a line connecting them at your disposal. Going through the center and back to the other periphery is possible, but usually takes too long. (e.g. 1h 30 min instead of 15 minutes by car).