UCLA's Institute of the Environment and Sustainability found something pretty amazing during Carmageddon I's 10-mile shutdown of the 405 Freeway last year: "air quality near the shuttered portion improved within minutes, reaching levels 83 percent better than on comparable weekends" and air quality improved 75 percent in parts of Santa Monica and West LA near the 405/10 interchange; because of reduced traffic all over, the entire SoCal basin, from Ventura to Yucaipa, Long Beach to Santa Clarita, was a full 25 percent cleaner. One of the lead researchers says in a release that "The air was amazingly clean that weekend ... Our measurements in Santa Monica were almost below what our instruments could detect, and the regional effect was significant." But it didn't last for long: "The effect was gone by the next week ... We measured fresh emissions: pollutants that come directly from cars. It's a very short-term effect."
Traffic during Carmageddon was down 90 percent on the 405 and down by double digits in many other areas, including parts of the Valley and Santa Clarita. The numbers show the importance of investing in hybrid and electric cars and reducing driving overall, according to the researchers. Unfortunately, UCLA won't be monitoring this weekend's Carmageddon II but said if scores of people ditch their cars this weekend we could have a repeat of that Hawaii-like air. "It has to be a significant, regional change, not just 10 miles of freeway closing ... It was really, really, really clean in Santa Monica [last time], and I don't think that was due just to the 405, because the wind blows in from the ocean. I think it was due to people not driving around Santa Monica."
· 'Carmaheaven': Closure of 405 in 2011 improved air quality up to 83 percent [UCLA Newsroom]
· Carmageddon II Archives [Curbed LA]