How to make tunnel on the track? I seems can not find it to create a tunnel on the coaster track.

I have Amd 550mhz processor, video card ATI Radeon VE 32mb. Nolimitscosster runs fine as long it is not too much structure in the front of me.Frame rate drops down when something happens like that. According Nolimitscoaster it does not makes any different if Pc has faster microprocessor than 500. I ...