I'm playing HL Episode 2 and I'm stuck...  I'm in a rail yard, with a
chopper hovering overhead dropping bomb-type things.  Alex appears
periodically and drops me med kits.  I figure that I supposed to get
to where she is and I've climbed up onto the rail car, over the
wrecked car, and have stacked boxes up so I can jump over to where
Alex is.  So far, I've been unable to as I always get stuck when I
jump and I can only jump back down.

What am I missing?  Is this what I'm supposed to be doing to get out
of the railyard?  HELP...

Thanks,

Dave