  The paper is devoted to isometric Banach-space-theoretical structure of
transportation cost (TC) spaces on finite metric spaces. The TC spaces are also
known as Arens-Eells, Lipschitz-free, or Wasserstein spaces. A new notion of a
roadmap pertinent to a transportation problem on a finite metric space has been
introduced and used to simplify proofs for the results on representation of TC
spaces as quotients of $\ell_1$ spaces on the edge set over the cycle space. A
Tolstoi-type theorem for roadmaps is proved, and directed subgraphs of the
canonical graphs, which are supports of maximal optimal roadmaps, are
characterized. Possible obstacles for a TC space on a finite metric space $X$
preventing them from containing subspaces isometric to $\ell_\infty^n$ have
been found in terms of the canonical graph of $X$. The fact that TC spaces on
diamond graphs do not contain $\ell_\infty^4$ isometrically has been derived.
In addition, a short overview of known results on the isometric structure of TC
spaces on finite metric spaces is presented.
