Thanks for your reply. I thought over what you said about using mods and I uninstalled the game and the mods. After downloading a new copy of the game I just played the game without mods and the game has run a lot better until I had several vehicles on different lines and then the stoppages started to reoccur but nowhere near the frequency as before.
After reading your e-mail this does explain the problem.
The game will not allow me to use the escape key to exit and I turn my computer off and restart.
About sending you the file. If I can work this out I will do so.
Regards and thanks