Underground Tunnel

Can anyone help me make an underground tunnel for a NL track im working on? any help is apreciated...

Track can't technically be built underground. It is possible to raise the entire terrain and coaster (move the track up, then go into the terraformer, select the corners of the map and press 'Mark area' and drag the terrain up to the track) and then build the track under the terrain, but still above 0 in the editor. This technique works, but it means you hit into the terrain as you go underground. It's much more effective if you just make a trench, and cover it up with 3ds. I don't have much experience with this, so i'm sure someone else could give you more details about this option.

yes i know that... what i wanted help with was how to make an underground tunnel out of 3ds...

The problem with using 3ds to simulate ground is that people often don't do it right/effectively and it ends up looking like crap.

Since you're new to this, you might just want to use something to cover up the ground collision, be it fog or a black plane. I've posted about this many times as it has been asked about many times, but I don't have the time to reanswer everything right now.