Many Americans can still remember the high prices, long lines and rationing of the 1973 oil crisis. OPEC’s embargo only lasted five months, but the 1974 National Maximum Speed Law intended to reduce fuel consumption kept speed limits on many interstates at 55 miles per hour (mph) for decades. While the benefits of lower speed limits for cars are still up for debate, researchers say speed limits on cargo ships could help reduce the impact of marine shipping on Earth’s climate and human health.
In a study published in ACS’ journal Environmental Science & Technology, David R. Crocker III and colleagues at the University of California, Riverside, found that 14 mph speed limits on container ships sailing near ports and coastlines would cut air pollution by up to 70 percent.
Their paper explains that while marine shipping is the most efficient way to move goods around the world, it’s also a significant source of air pollutants. The more than 100,000 ships – some of them longer than three football fields – that move 90 percent of the world’s cargo burn low-grade fuels that produce large amounts of air pollutants. Among them are carbon dioxide, a greenhouse gas; nitrogen oxides and sulfur oxides that contribute to acid rain; and particulate matter that can cause respiratory and other health problems.
A ship’s speed is directly proportional to the cube of its fuel consumption, so if a ship revs up its engines to go twice as fast, it burns eight times more fuel. That means that even small reductions in speed can significantly reduce air pollution.
Crocker’s team showed that a 14 mph speed limit could reduce container ships’ emissions of carbon dioxide by about 60 percent and nitrogen oxides by 55 percent, compared to emissions at their normal cruising speeds between 25 and 29 mph. Particulate matter emissions fell by nearly 70 percent.
The group hopes that imposing these speed limits on vessels near ports and coastlines could significantly reduce their pollution and protect the health of people living in those areas.
Do you think speed limits on ships could be an effective way to limit their consequences on human health and climate? Should we think again about lower speed limits for cars and other vehicles?