The literature on modal choice analysis of freight transport has revealed that the freight transport market is highly diverse. Aggregation over heterogeneous commodity types can cause a bias in the estimation of models. Therefore, disaggregation over commodity groups has been the norm and different models developed. In some cases, however, aggregate models might be preferable because they are less costly and may be adequate for prediction. The present paper attempts to improve our understanding of this area by investigating the desirability of aggregation over commodity groups.