For these data there was no major effect on the transition lengths or the coefficients due to the use of vertical rather than spill-through abutments. The exceptions to this statement were three vertical-abutment cases in the narrow-opening class for which square corners were used. The square-cornered abutments were a deliberate attempt to model a very severe situation. Because the RMA-2 program, or any two-dimensional numerical model for that matter, is not well-formulated to handle such drastic boundary conditions, no general conclusions should be drawn from these cases about actual field sites having such a configuration.