Subject: What would be the challenges for a gravity train on the moon?

The basic concept of the gravity train as proposed by Hooke to Newton is 
exciting but seems impossible to engineer on Earth.  The liquid core is a big 
problem, as is the need to empty all the air out of the tunnel to eliminate 
friction from the air.  Both of those problems are non-existent on the Moon, 
however.  Would it be possible with today's technology to construct a gravity 
train through the Moon?  (Assuming there was a practical need for such a 
train.)  If not, what new technologies would need to be invented?  What 
engineering problems would have to be overcome?

Re: What would be the challenges for a gravity train on the moon?