Check this video out about Relativity - Time Dilation and Length Contraction
Neither the train or tunnel have stretched or shrunk. The only thing that has changed is your perception of time by altering your speed from inside
the train verses reality's perception of you (or from the tunnels point of view) this causes a bend or warp in space time or at least the perception
of it, which causes you to believe what you saw was really a short and or long train and or tunnel. And since seeing is believing you believe time and
or space has altered when in reality it is only your point of view verses reality's point of view (or perception) of you that has changed.
[edit on 6-6-2010 by AsTaR]