Tunnels, the easiest method is to dig a trench in the terrain and then cover the top with "ground boxes" or models.
About all I can think to suggest is... learn to use ground boxes. If the mtmg link didn't suit you then see the Traxx help file.
>> trucks keep on falling through the bridges
I don't know what you are using for a bridge, though i could probably guess.
Perhaps someone should do a little write up about the various methods used for
bridge building (I'm not feeling up to it). Covering groundboxes, individual rectanglar models used as modular pieces (roads & railings), unusual shaped whole bridges set to non-collide and using special collision property methods, etc.
<small>Thanks for being gracious about the name change.
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