California state law requires that the Bay Area reduce its overall level of air pollution 15 percent by 2035. Precisely how local officials are going to get there from here is still largely up for debate.
Regional pollution control officers are faced with a number of options as how to do that. One suggestion being kicked around by the Metropolitan Transportation Commission, the regional intra-governmental body tasked with getting helping the Bay Area comply with the state's goal, is dropping the speed limit on Bay Area highways from 65 mph down to 55 mph.
"A good portion of the Bay Area travel is on the freeway, and a good portion of that is spent moving over 55 miles per hour," Amir Fanai of the Bay Area Air Quality Management District told the San Francisco Examiner. "If we could reduce the speed limit by 10 miles per hour, it would have a major impact on our air quality."
Fanani noted that because vehicles reach their optimum efficiency between 40 and 55 mph, moving from 55 to 65 mph could as much as double emissions. Dropping the limit could reduce overall air pollution in the area by six percent.
A 2008 study published in Atmospheric Environment found a significant decrease in levels of air pollution surrounding an Amsterdam highway after the speed limit was decreased from 100 kph to 80 kph (approximately 62 mph to 40 mph).
The Metropolitan Transportation Commission's John Goodwin told CBS San Francisco that while reduced speed limits are currently being looked at, it's only one of a litany of possible options under consideration.
Like most other states, California capped the speed limit on its highways at 55 mph in the early 1970s, when Congress made the lower speed a prerequisite for receiving federal highway funds. However, by the mid-1990s, the majority of California freeways had raised their maximum speeds to 65 mph.