Unintended environmental impacts of nighttime freight logistics activities

In recent years, the reduction of freight vehicle trips during peak hours has been a common policy goal. To this end, policies have been implemented to shift logistics operations to nighttime hours. The purpose of such policies has generally been to mitigate congestion and environmental impacts. However, the atmospheric boundary layer is generally more stable during the night than the day. Consequently, shifting logistics operations to the night may increase 24‐hour average concentrations of diesel exhaust pollutants in many locations. This paper presents realistic scenarios for two California cities, which provide exhaust concentration and human intake estimates after temporal redistributions of daily logistics operations. Estimates are made for multiple redistribution patterns, including from 07:00‐19:00 to 19:00‐0:700, similar to daytime congestion charging polices and from 03:00‐18:00 to 18:00‐03:00, corresponding to the PierPASS program at the ports of Los Angeles and Long Beach. Results for these two redistribution scenarios indicate that 24‐hour average exhaust concentrations would increase at most locations in California, and daily human intake is likely to worsen or be unimproved at best. These results are shown to be worse for inland than coastal settings, due to differences in meteorology. Traffic congestion effects are accounted for, using a new graphical method, which depicts how off‐peak policies can be environmentally improving or damaging, depending on traffic speeds and meteorology. An investigation into the decreasing marginal environmental benefits of off‐policies is then provided, through the application of traffic flow theory. Finally, related environmental and human exposure concerns are considered to provide a comprehensive policy discussion of the environmental effects of shifting logistics operations from day to night.