The SV vehicles are very wide and have widely spaced wheels on the axle. This means that, with shallow fill depth, the action of the two wheels do not overlap. The distribution within Archie was built on the assumption (reasonable for all other loads) that the distributions do overlap. The distribution width is worked out as Axle track +1.5m + depth from wheel to extrados.
There is a further complication in this because the rules in BD21 sa that the load can be treated as a UDL across the full width once the loads are combined. Load transfer due to centrifugal action is thus cancelled. If that assumption is invalid, the effect must be taken into account. As with railway loading, the simplest way to deal with this is to treat wheel loads rather than axle loads. I will therefore build a set of SV load files based on wheels instead of axles, but users must then be sure to restrict the "bridge width" used appropriately for half a vehicle.