During the pandemic, as many as 100 giant container ships would idle off the Southern California coast, belching pollutants as they waited for a berth to unload cargo at the twin ports of Los Angeles and Long Beach. But traffic on the marine equivalent of LA’s perpetually clogged 405 freeway dissipated once officials implemented an OpenTable-style system that reserves a place in line at the ports for arriving vessels. 

Now, researchers have calculated that the queuing system at the busiest seaport complex in the U.S. is also paying a climate dividend, reducing estimated carbon dioxide emissions by as much as 24% per voyage between East Asia and Southern California. 

Before the launch of the queuing program in 2021, the twin ports, along with most other ports around the world, relied on a century-old first-come, first-served approach to assigning dock space that encouraged ships to “sail fast, then wait,” according to the researchers. But since the queuing system tracks a vessel’s journey as it departs its last port of call, captains can slow down without fear of losing their spot in line. That reduces fuel consumption and emissions. 

“One of the big wins of this is that it’s really sort of a low-tech, low-hanging-fruit way to cut emissions for the shipping industry,” said Rachel Rhodes, lead author of the peer-reviewed paper published last week in the journal Marine Pollution Bulletin.

Ships transport more than 80% of the world’s trade in goods and account for about 3% of global greenhouse gas emissions, an amount greater than Japan’s share. Many technologies that shipping companies are testing to curtail emissions, such as onboard carbon capture, biofuels and high-tech sails, tend to be complex and costly with an uncertain return on investment. 

Logistical tweaks such as the queuing system, though, are relatively inexpensive. It costs around $300,000 annually to operate the Los Angeles initiative, according to the ports, which have funded the program through 2027.

Slowing down 

Rhodes, a project scientist at the Benioff Ocean Science Laboratory at the University of California at Santa Barbara, and her colleagues analyzed 125 million location records generated by 1,157 container ships as they made voyages from East Asia to Los Angeles between 2017 and 2023.  By integrating data on vessel size, cargo capacity and engine type, the scientists were able to estimate CO2 emissions for each of 10,000 journeys taken before and after the queuing system took effect.

They found that emissions per voyage dropped by 24% in 2022 and nearly 16% in 2023.

The researchers determined that average ship speed fell from 18.6 knots to 15.9 knots in 2022 and to 17.6 knots in 2023. That’s also a win for whales: Slower speeds can result in fewer fatal collisions with the giant marine mammals.

“Ships are still going pretty fast, but every knot does help,” said Rhodes. 

While the queuing program is voluntary, more than 95% of shipping companies docking at the two ports participated, Rhodes said. The researchers acknowledged that other factors, including companies’ climate and business priorities and the type of vessels they operate, can affect ship speed and emissions. They also found that four smaller West Coast ports that don’t deploy a queuing system also experienced overall drops in emissions. 

Will it work at other ports? 

The Port of Oakland in California began using Los Angeles’ queuing system in 2022, and the Port of Rotterdam in the Netherlands last October began automatically assigning ships docking times once they come within 276 miles (444 kilometers) of the harbor. 

But most ports still rely on first-come, first-served to allocate berths, and it remains to be seen how widely queuing will be adopted worldwide, according to Valerie Thomas, a professor of industrial engineering at the Georgia Institute of Technology who researches sustainable shipping solutions. 

The program may not be easy to replicate elsewhere, she said, noting it was developed during the pandemic when shipping companies were motivated to adopt measures to reduce congestion at an already jam-packed port. “This type of regulation might not even encourage slower speeds at all if there is no congestion problem,” added Thomas, who wasn’t involved in the California port study. 

Implementing a queuing program, though, can be done quickly, according to Los Angeles port officials. It took just 27 days to design and launch the system, which relies on existing tracking technology required for all large ships. 

“It's really quite a cheap solution compared to other options,” said Rhodes.