@twofl: Same for me. In general the game is running quite ok, I’m having something around 60-30 fps, as long as I don’t open any dialog windows. But when I open the lines dialog, it instantly drops from 60 to 15 fps. The vehicles dialog is the same. The other dialog windows from the bottom left menu also have a negative influence on the fps. I have about 300 vehicles running and this seems to become worse the more you have. So there must be something wrong with windows that contain calculation numbers, as you said.
Buying new vehicles is also a killer. The purchase dialog brings it down from 60 to 40 fps. Then with every vehicle bought one of those “picture in picture” windows opens up, which results in a drop of another 2-4 fps. Then after buying about 10 vehicles it becomes unplayable slow. I’d love to see an option to switch off that “picture in picture” thingy. Or even better, an option to switch it off in general an a button in every window to enable it in on demand.
Hope they find the reason why the game gets so slow under these conditions. It really kills the fun for me :/