Energy Consumed in Freight Transport: Estimates from Shipper Surveys
C Rizet, INRETS DEST, FR
Effective intervention in order to reduce freight transport impacts requires in-depth knowledge of the factors that determine the logistical decisions made by firms. Using data from 19999 shipper surveys, energy consumption is estimted for a sample of shipment and analyzed in relation to the logistical choices made by shippers to quantify the influence of logistical practices on freight transport energy consumption..
Shipper surveys developped by Inrets describe both the journeys, in terms of the transport chains, and the principal characteristics of the shippers who send consignments. With a view to improving the method employed in this type of survey, two test surveys were conducted in France 1998-99, each involving slightly more than 200 firms and 600 shipments. On the basis of these surveys different aspects of transport demand (consignments) can be quantified and this demand can be related to the principal logistical characteristics of the shipping companies. The surveys were not designed to cover energy consumption, but they nevertheless provide precise details about transport in terms of the routes taken, any consolidation or logistical services that are performed and the types of vehicle used. They enabled to estimate the amount of energy consumed in the transport of each consignment.
Method of computing per consignment energy consumption
Energy consumed for the transport of a shipment has been estimated in four stages:
* estimation of the consumption functions for each type of vehicle, in litres of fuel per 100 km on the basis of the total weight (unladen weight plus the weight of the load);
* calculation of the energy consumed by the vehicle on the leg, on the basis of the distance covered and the total weight of the vehicle. For road legs an estimated deadhead return run rate is applied for each type of vehicle and type of transport organization (own account or hire and reward) on the basis of the results from the national road freight transport survey;
* a proportion of the consumed fuel is then assigned to the consignment, on the basis of the percentage of the total load it represents;
* finally, the energy consumptions of all the legs in the transport chain are summed for the consignment.
It was in fact only possible to apply this method to road legs. For other modes, we simply applied a per tonne-kilometre average consumptions for each mode using french figures.
Consumption functions for each type of vehicle
On the basis of published work, we have analyzed the specific consumptions for each vehicle. We have given precedence to work conducted in the framework of the European MEET project which provides methods for estimating consumption. Using published research it is possible to obtain an estimate of energy consumption which is fairly accurate for road transport but much less so for other modes (rail, waterways, sea and air). In order to exploit the surveys a simplified method for estimating the energy consumption for a consignment was implemented which made use of available variables.
Average unitary consumptions, for each transport leg and transport chain
The unitary consumption for a shipment is the energy used in order to transport the consignment, in grams of oil equivalent, divided by the number of tonne-kilometres travelled (goe/tkm). In the case of road legs the unitary consumption figures vary greatly
? from 20 to more than 100,000 goe/tkm. The average unitary consumptions for a type of consignment are computed by weighting the consumption for a consignment by its kilometre tonnage. These average values can be computed either for each transport chain or for each transport leg, with summing of the energy consumption for each leg. The variability of unitary consumptions for road transport legs means that the computation of average consumptions for a type of consignment is very imprecise. For legs that use other modes our highly simplified data fail to show this variability, but it must nevertheless exist in reality.
* The average consumptions for all road legs are similar in both the surveys we used, in spite of the considerable differences between the samples: 34 to 36 goe/tkm in the case of own account transport, 28 to 30 in the case of hire and reward transport, i.e. 30 goe/tkm for road transport as a whole.
* For all transport chains, as a result of weighting, end legs make a relatively minor contribution to unitary consumption: the average values are still about 30 goe/tkm for exclusively road chains and the values for the other modes are similar to those used for the principal mode: around 500 goe/tkm for air chains, 13 for river transport, 8 to 16 for rail (depending on the percentage of full trains), 10 to 12 for rail-road combined transport, 5 for sea transport.
* Unitary consumptions have been related to kilometre tonnages on the basis of the distance covered by the consignment on transport networks. We have also related them to kilometre tonnages on the basis of straight-line distances (per/tkmSL) in order to assess the impact of the roundabout route followed by consignments either because of the networks, or because they need to transit through a terminal in order to be grouped together, which generally involves an additional distance between the consignment?s origin and final destination. By comparing the unitary consumptions for these two types of distance (straight line and network distance), we can measure the ?excess consumption? caused by the lengthening of distances because of the form of the networks or because of passing through a transhipment point. In the case of road chains, this unitary excess consumption amounts to 29%; for own transport operations, we have confirmed that excess consumption is greater in the case of chains with multiple legs (44 and 54% respectively for the NPDC and Mystic Surveys) than for chains with a single leg (21 and 26%).
The influence of logistical choices on energy consumption By using the average consumption data we have been able to assess the influence of some major logistical tendencies on transport energy consumption. Two major tendencies provide a good illustration of the potential of our approach: the grouping of consignments and the just-in-time approach.
To assess the influence of consolidating the shipments (massification of flows), we have compared the average unitary consumption of consignments which have been grouped together with the average unitary consumption of consignments which have not. As we only consider road consignments, which are more homogeneous, it is apparent that the consolidated shipments consume considerably more energy than the non-grouped consignments. This is explained by the fact that the average weight of grouped consignments is very low and even when grouped together, the total weight of the load is still lower than the weight of ungrouped consignments. To simulate the influence of grouping on unitary fuel consumption, we then computed what energy the consignments that we observed consolidated would have consumed if they had been transported on their own (without consolidation) and also the lengthening of the distances which results from grouping. Thus, the average effect of grouping is to reduce energy consumption by a factor of between 3 and 4 as a result of the combined effect of the reduction in consumption caused by the increase in the weight of the load and the increase in consumption caused by the lengthening of distances.
Just-in-time (JIT) practices are identified on the basis of a question in the survey that dealt with the delivery time requested by the customer. The two results are : firstly, the average weight of consignments is lower when the delivery time is short and, secondly, the average unitary consumptions seem to follow the same trend, however, the accuracy of the estimators of average consumption on the basis of delivery time is so low that it is not possible to reach a conclusion on this point.
Improvements to be incorporated into the new shipper survey Previous shipper surveys followed the different legs in the journey but they were not designed to allow analysis of the energy used to transport the observed consignments. From this research, marginal improvements were designed that will permit more accurate analysis of energy consumption for new surveys. These improvements relate, on the one hand, to the information which is required to estimate energy consumption (which is collected in the transportation legs questionnaires) and, on the other hand, to some characteristics of the consignment or the firm which explain logistical behaviour.
A new survey is being launched in France this year (2003) ; these data will enabled a deep anlysis and modelling of energy consumed in freight transport.
Association for European Transport