Impact of fleet composition and road network on efficient use of larger and heavier trucks in forestry transport

Sustainable forestry is fundamental for the supply of raw materials for sustainable products such as wooden houses, packaging, and biofuels. Efficient transport is vital for sustainable forestry, as road transports of roundwood from the forest to recipient industries account for 50% of CO2 emissions and 40% of the costs for harvesting and transport. Transport of roundwood is characterised by deliveries from many sources to few industries. As wood is heavy, weight generally restricts load capacity, and an increase in gross vehicle weight of log trucks to increase payloads may reduce costs and emissions. Limitations in road bearing capacity might necessitate detours and longer driving distances if the full load capacity of heavier trucks is to be used. To comply with road regulations, heavier trucks must have more axles, which increases investment cost, rolling resistance and tare weight, and thereby transport costs and emissions per vehicle-km. If larger trucks are used on roads with low bearing capacity, their payloads are lower than for standard 7-axle trucks. We studied how truck fleets with a mix of truck sizes can be used to reduce costs and the influence of the road bearing capacity using a discrete event simulation model developed for a case in Sweden. A base scenario with a fleet of 7-axle vehicles was compared to nine alternative fleet compositions using three performance indicators: cost per m3, distance driven per m3, and time per m3. These fleets were operated on three road networks: A, the current mix of 64-tonne and 74-tonne roads; B, major roads upgraded to 74 tonnes; and C, all roads upgraded to 74 tonnes. Results show that adapting the fleet composition to the available road network is beneficial from work time, fuel consumption and cost perspectives. Although it is beneficial to strive for heavier vehicles, the road network restricts the number that are useful. When heavier vehicles are used on 64-tonne roads there will be losses in terms of costs, fuel consumption, and payload. For the current road network, a fleet of 7- and 9-axle vehicles will be preferable if transports can be planned. Upgrading roads from 64 to 74 tonne bearing capacity will decrease work time, distance travelled, and costs per m3 transported. When considering societal costs for road upgrades, the benefit will probably be smaller for less used roads. As the design of a truck fleet is complex, simulation is a useful tool to assist hauliers in evaluating fleet compositions.