CARB study urges managing congestion, speed for cleaner air

| 9/11/2007

A study commissioned by the California Air Resources Board examined the link between vehicle speeds and greenhouse gas emissions, showing a relative “sweet spot” of medium speed and minimal emissions, CARB announced this week.

The announcement came during CARB’s Chair Air Pollution Seminar on Tuesday, Sept. 11, scheduled to be given by Matthew Barth, professor and director of the College of Engineering-Center for Environmental Research and Technology at the University of California-Riverside.

The university used GPS tracking combined with emissions testing to consider what possible traffic operation strategies could reduce on-road carbon dioxide emissions.

The study found that lowest carbon dioxide emissions occur when vehicles are driving between 35 and 55 miles per hour, when they emit less than 300 grams of carbon dioxide per mile. The vehicles emitted as much as 800 grams of carbon dioxide per mile at 5 mph and 500 grams at 85 mph.

Some congestion helps keep speeds and emissions down, the study found, while too much dramatically increases greenhouse gases emitted from cars.

“If congestion brings average speed down from a free flow speed of around 65 mph to 45-50 mph, then congestion is actually helping improve fuel consumption and emissions,” the presentation read.

California could decrease carbon-based emissions by using a combination of congestion mitigation strategies and speed management techniques, the report noted.

“If the real-world, stop-and-go velocity pattern of vehicles were somehow smoothed out where average speed was preserved, then significant fuel consumption and emissions savings could be achieved,” the study concluded.

Tuesday’s report could lead to future actions by CARB.

CARB has written and enacted several regulations based on evidence from research it commissioned through California educational institutions. Through California Assembly Bill 32, the agency has the power to write, enact and enforce rules that address greenhouse gas emissions and global warming.

– By Charlie Morasch, staff writer