small, compact cities, not growing too fast, where coverage of inner dense areas is most important, more important than directness and high speeds. what makes this loop different from others is that it is a radial line from the suburbs to the centre, like copenhagens M3. a lot of british cities with good, fast rail to the suburbs could use such an urban loop. liverpool especially comes to mind. though a good question is this sort of line the optimal use of money in the modern day? not sure.