Air quality improvement via modal shift: Assessment of rail-water-port integrated system planning in Shenzhen, China

The escalating concerns regarding air pollution problems surrounding port cities have attracted much research attention. The Port of Shenzhen is one of the busiest container ports worldwide, only third to Shanghai and Singapore globally. However, 70% of the freight transportation demand is satisfied via on-road trucks, leading to serious traffic congestion, road accidents and air pollution issues in the city of Shenzhen. This study aims to assess the environmental benefits of modal shift of port-connecting freight transportation by increasing the use of rail and waterborne systems in Shenzhen. To evaluate the environmental benefits of the multimodal transportation strategy in 2025, we employed traffic datasets with a high spatial resolution and a transportation demand model to establish emission inventories and applied them in air quality simulations. Our results indicate that the implementation of multimodal transportation systems could notably reduce the truck volume along major freight corridors, except for roads adjacent to the planned inland ports. The freight traffic activities along the major freight corridors are reduced by nearly 70% over the original freight volume, resulting in a drastic reduction in the emission intensity. Under the most progressive policy-enhanced strategy (PPP) scenario, the total well-to-wheel (WTW) NO_X, fine particulate matter (PM_2.5) and CO₂ emissions could be reduced by 8881 t, 104.8 t and 688 × 10³ t, respectively. The NO₂ concentration in traffic-intensive areas could be reduced by 5 μg/m³, and the 8-h maximum O₃ concentration could be reduced by 0.34 μg/m³ on the average (up to 1.1 μg/m³ in certain areas). Our research indicates that a shift from traditional road transport to cleaner railway and waterway transport could deliver transportation and environmental benefits to port cities.