  For every d-dimensional polytope P with centrally symmetric facets we can
associate a "subway map" such that every line of this "subway" corresponds to
set of facets parallel to one of ridges P. The belt diameter of P is the
maximal number of line changes that you need to do in order to get from one
station to another.
  In this paper we prove that belt diameter of d-dimensional space-filling
zonotope is not greater than $\lceil \log_2\frac45d\rceil$. Moreover we show
that this bound can not be improved in dimensions d at most 6.
