This research is based on a real case study of horizontal collaboration in France. The project involves several suppliers who form a geographical cluster and wish to pool the delivery of their goods to several thousands of customers spread across the whole country. The main objective is to build pooled load plans that cut distribution costs through volume consolidation. The distribution system includes one consolidation facility in the production area and a set of intermediate facilities called regional distribution centers (RDCs). It combines full truckload (FTL) routes between the production area and the RDCs and less-than-truckload (LTL) shipments from the RDCs to each customer. We propose a Mixed Integer Linear Programming formulation for the optimal location of RDCs. This model integrates the two transportation rate structures and enables direct deliveries from the production area to customers when FTL routes are not profitable. We propose two additional constraints that help decision makers to refine their preferences. We present computational experiments on a case study concerning the distribution of horticultural products in France.