Relay transport network design for sustainable trucking industry considering carbon emissions and driver working conditions

Relay transport is an emerging collaborative approach that divides traditional long-haul shipments into multiple shorter segments, each handled by a different truck driver. By jointly completing shipments and enabling the shared use of transportation resources, this approach has the potential to alleviate operational inefficiencies, environmental pollution, and poor driver working conditions in the trucking industry. However, existing studies on relay transport network design primarily concentrate on the operational perspective of private companies. To address environmental and social issues in the trucking sector, this study proposes a bi-level programming model to develop a sustainable relay transport network that accounts for carbon reduction targets, carbon tax policies, driver work regulations, relay point capacity limits, and investment budgets. The upper-level government agency aims to minimize carbon emissions, driver overtime hours, driver overnight stays, and infrastructure construction costs by determining the number, location, and capacity of relay points. The lower-level trucking companies select freight transport routes based on the given network configuration, influenced by transport costs, cargo transit times, and carbon taxes. The model is solved using a genetic algorithm integrated with the method of successive averages. A case study in Japan identifies 22 relay points (14 small, 7 medium, 1 large). The optimized relay transport network offers substantial improvements compared to the traditional direct transport network, achieving reductions of 40.48 % in carbon emissions, 53.21 % in driver overtime hours, 70.38 % in driver overnight stays, 20.07 % in operational costs, and 5.13 % in total cargo transit times. Sensitivity analyses highlight the positive impact of appropriate relay point capacity and higher carbon tax on the network's sustainability performance. These findings offer valuable insights for government agencies to configure relay transport networks and support policymaking for sustainable freight transport planning.