Capacity Utilisation, Empty Trips - Modelling Approaches and Empirical Evidence from Danish HGV Trip Diaries
O Kveiborg, COWI; M Abera Abate, DTU Transport, DK
The paper adresses modelling techniques illustrating capacity utilisation and empty trips. Two approaches: transport modeling and economic modeling are discussed and empirical evidence from Danish travel diaries is used to highlight specific issues.
The recent years' focus on congestion on European roads and the increased awareness of the large negative environmental impacts the continuous increase in traffic by trucks have called for new insights and new sorts of regulation. From an overall look at HGV transport statistics two things catch the eye. First the relatively low utilization rate and secondly, the relatively large number of empty vehicle kilometers. It is beyond doubt that improvements in both of these will lead to less congestion and less environmental damages. However, rather little is known about the reasons for these low figures.
From an economic point of view and also within freight transport modeling it is often argued that the freight transport industry operates under perfect competition. This implies that the choices made within this industry should be (economically) optimal. Hence, choices of load factors and vehicle routing including empty trips should be at their optimal level seen from the firm side. This has also been demonstrated qualitatively in the literature. However, again it has not been tested to any large extent and the modeling literature have only to a very limited extent tried to describe the real driving forces within individual firms. This implies that it is rather difficult to identify the extent of sub-optimal behavior of the firms and (especially) if an outside regulator has any possibility of removing barriers that prevents the operators from improving on both utilization and empty trips.
This paper reviews existing modeling literature with primary focus on capacity utilization and empty running. It takes into consideration both a transport modeling approach and a microeconomic modeling approach. The purposes of these two strands of literature are quite different. The transport modeling literature aims at predicting freight traffic. The models can be used to predict traffic changes following policy changes and infrastructure investments etc. A crucial element for these models is then to predict both the load of vehicles to convert transport to traffic and to know how many empty trips accompany loaded trips. A recent strand of literature aims at modeling the logistics element. The other strand of literature uses microeconomic models to specifically model the firms' decision of vehicle use. For example by modeling the firms choice of accessing a market (where to pick up a load) and given this choice what vehicles can be used to perform the trip. The decisions are based on operation costs, market prices etc. In some models the vehicle fleet is given, but in the long term also the fleet composition is variable. Hence, this modeling approach aims at determining the optimal fleet composition given the trips that must be performed. This latter strand of literature has not yet found its way into freight transport modeling.
The review is accompanied with some empirical evidence from a Danish trip diary of HGV from which e.g. relationships between type of vehicle, type of good carried, firm size and the vehicle use including capacity utilization and empty trips. Our data enables us to identify relationships not previously brought forward in the literature (that we have found). This empirical analyses aims at outlining modeling possibilities that can overcome the divergence between the above mentioned strands of literature.
Association for European Transport