I don’t use hard difficulty, GC… Normally i choose easy and medium or large map. Never tried two circular city bus/tram lines, i found that a back and forth line always works well. Usually the balance for my city bus/tram lines is in the green. Here is my setup of a city tramline at average. 40 stops counting both sides of the streets, 5 trams, 3 minutes frequency: http://sectionf8.com/f86files/tftramline.jpg
Line usage heavily depends of course. Currently on a large map with only about 40% of the cities running a bus/tramline. Lowest is 33% highest 76%. Working on it. 😉
I played TF right from the day it was released. Great fun but the traffic jams and a few other annoyances made me quit for more than a year in favor of TS. I was very pleasantly surprised when i tried TF again after the big upgrade. So much better, certainly regarding passenger transportation as well, be it by rail or road.
If you have not tried a back and forth city bus/tram line i can certainly recommend it.
cheers,
Jan