Investigation of a port queuing system on CO₂ emissions from container shipping

The maritime shipping industry is pursuing a diversity of strategies to meet its decarbonization goals, yet inefficiencies like traditional "first-come, first-served" port arrival systems, which encourages vessels to race to port to wait offshore, remain largely unaddressed despite their significant emissions impact. In 2021, the Ports of Los Angeles and Long Beach implemented a new queuing system for container ships that instead assigns predetermined positions when vessels depart their last port of call. Our research evaluates whether this system, implemented primarily to reduce port congestion during major disruptions, also reduces CO₂ emissions during transpacific voyages by enabling vessels to optimize speed. To examine this, we applied a bottom-up emissions model using vessel technical specifications and Automatic Identification System (AIS) data from 10,000 voyages by 1157 container ships across 6.5 years (2017-2023). We compared emissions before and after the new system was implemented at Los Angeles and Long Beach, observing 16-24 % reductions in emissions per voyage post-implementation, and compared emissions trends at three control ports along the West Coast of North America without similar systems. These comparison ports showed moderate emissions reductions, suggesting these decreases can be attributed to multiple combined factors (e.g. rising fuel prices, changing trade volumes, and new emissions regulations). We additionally found substantial variation in emissions efficiency among major ocean carriers, highlighting the influence of company-specific practices. Finally, we examine how additional queuing system modifications could even further reduce emissions.