On my current map i’ve experienced some places, where the game begins to stutter like hell. I think it has something to do with the briges for trains.
Everytime i am passing areas on the map, where i’ve build a lot of bridges and tracks, the frames are heavily dropping down to ~1 fps and it stutters. I could offer a savegame file to check this by yourself.
After passing those areas with bridges, the framerate stabilizes itself at a high rate.
Windows 7 x86-64, 8 GiB RAM, NV GTX 760 @ 1920x1200p60 maxed and limited details (both the same resulting framedrop/stuttering).