Nice idea. But, are you talking about only a few tunnels? Like, maybe to get to one country from another easily? Or just, everywhere?
If everywhere, tunnels would collide with each other.
And then, where would all the dirt, rock, and everything else go?
I'm glad to see that you are thinking about our fuel problems. That's great. If someone could get it to work without killing us with g-forces, or whatever, it could possibly be worth it, if it could save enough fuel.
And, what about animals that could get trapped down there?