I avoid the norlunga and adelaide to millswood(?) lines because of how slow my system is. It also tends to do it on the highland valley, and australia maps, robe iron ore it handles with ease(go figure with the size, but low detail).
To explain, my system has never lived up to what it should have been. It originally had an ATi video card that would not run OpenGL at all, and lagged like hell at the best of times. Now with me running 2000 (ONLY stable windows i've ever encountered) it seems to have issues with Nvidia and DirectX. I've debugged and had a friend who provides tech support for a living look at it, and neither of us has found anything to explain why the machine has never run properly (doesn't crash, but just gets very slow, and overheats(now fixed)).
Saying that, the machine is rock solid for work, so it has full filled the need as a school computer.