For each combination of mode and commodity group, we have flows, in tons per annum, for direct long- and short-haul trips, relative to the coarse zoning system. We also have flows, in tons per annum from each coarse zone to each TLN and from each TLN to every coarse zone.

CUBE Cargo uses all this flow information to produce matrices of flows, in tons per annum, in the fine zoning system.

The process begins by calculating a weight for each fine zone. The weights are based on the tables Para.FinFunPara and Fine.FineSocEcoData.

Given a coarse zone, j, the three allowed relationships to the fine zoning system are:

•Aggregation: The coarse zone, j, is a member of a set, j, of coarse zones, which make up fine zone, k. In any translation from the coarse zoning system to the fine zoning system, the flows to or from k are found by summation over the members of j.

•One-One: The coarse zone, j, is the fine zone k. Note that this situation may be treated as a special case of aggregation; as a special case of disaggregation; or as a third case without changing the model results. In any translation from the coarse zoning system, the flows to or from k are the trips to or from j.

•Disaggregation: The coarse zone, j, contains a set, k, of fine zones. In this case, the trips to or from j are distributed among members of k in proportion to their weights.

Note that, although other cases can be envisaged (that is, coarse and fine zone boundaries do not coincide), CUBE Cargo explicitly disallows them.

Similar considerations apply to TLNs except that TLNs are either one-one with a fine zone or aggregated into a fine zone; they cannot be disaggregated from several fine zones.

When dealing with a movement from i to j in a coarse zone matrix, where both i and j are disaggregated into fine zones, the procedure above yields the trip ends of a small sub-matrix of the fine zone matrix, but it does not yield the cell-by-cell values. A gravity model (with a negative exponential deterrence function of distance, parameterized by values from Para.ParaFineDis) is used to fill in the individual cell values.

Note several manipulations can be used to override the default behavior of the fine distribution model. Singular points can be defined for road traffic, which add a constant to the weight assigned to a fine zone for a particular commodity and direction. Singular points can be defined for ship or rail traffic, which replace the calculated weight assigned to a fine zone for a particular commodity and direction. Finally, it is possible to define a singular origin-destination pair where the coded value replaces the model output volume for a given commodity group and for a specified trip category. The categories available for overwriting are short-haul direct; long-haul direct; short-haul to TLN or short-haul from TLN.

The fine distribution model does not run differently in forecast and non-forecast modes.