This should not be a surprise because the more you add the harder your graphics card has to work. Once it gets to the limit of its ability your will start to see jerky pictures as the graphics card struggles to render the scene.
Make sure that you have better than the minimum system requirements for the game and use the options menu to turn down the performance settings. Also check that your graphics card drivers are up to date and try switching between OpenGL and Directx (if this option is still available in TR212 )
thank you for the tips ,my video card is a AMD Radeon HD 6800 series but i only have 4094MB ram . wich is well below the system requirements , goin to up grade it tomorrow . switched to openGL from DirectX
I'd just like to mention 4094MB of RAM is much higher than you think. 4000MB is 4G of RAM. 4094 is 4.94GB of RAM which is plenty to run Trainz on. I run TS12 on an Nvidia 460M 3G VGA with 16G of RAM. And Trainz only uses 1G of RAM and TADDaemon is using pretty much the same amount. It's not the RAM that's the problem. It'd most likely be your processor and/or Graphics card.