  The surface free energies, interfacial tensions and correlation lengths of
the Andrews-Baxter-Forrester models in regimes III and IV are calculated with
fixed boundary conditions. The interfacial tensions are calculated between
arbitrary phases and are shown to be additive. The associated critical
exponents are given by $2-\alpha_s=\mu=\nu$ with $\nu=(L+1)/4$ in regime III
and $4-2\alpha_s=\mu=\nu$ with $\nu=(L+1)/2$ in regime IV. Our results are
obtained using general commuting transfer matrix and inversion relation methods
that may be applied to other solvable lattice models.
