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COVID-19’s Silver Lining: Better air quality, less traffic, safer highways

coverSilicon Valley Traffic Down 94%; Mileage Drops 75%; Crashes Down 63%

June 2, 2020 – Joint Venture Silicon Valley’s Institute for Regional Studies today published a new report, COVID-19 Impacts in Silicon Valley: Transportation, Emissions & Air Quality, that reveals an upside to the Silicon Valley shelter-in-place orders implemented in March due to the COVID-19 pandemic. The report examines the reduction in Silicon Valley’s regional ground and air transportation, declines in traffic delays, as well as the impact of those reductions on transportation-related injury crashes, regional air quality, and greenhouse gas emissions. The Institute analysis presents these impacts in the context of historical trends, where possible.

“We certainly don’t intend to minimize the tragedy of the pandemic,” said Rachel Massaro, the Institute’s Director of Research. “And yet, there is an opportunity to delve into the merits of having fewer cars on the road. Understanding the impacts of reduced transportation on emissions and air quality can help shape our future behavior, and potentially inform policies around telecommuting.”

Key Findings

  • Per capita freeway vehicle miles traveled (VMT) in April was lower than any other time in the 17-year dataset; March and April declines were greater in Silicon Valley (41% below 2019 values) than in the Bay Area (down 30%) or California overall (down 28%). Between January and mid-May, Silicon Valley freeway VMT declined by 41%; all-road VMT declined by 75-76%.
  • Daily vehicle hours of delay in April were lower than any other time in the nearly 20-year dataset, with average daily delays on Silicon Valley, Bay Area, and California freeways reduced by 94%, 86%, and 81%, respectively, since February.
  • Transportation-related injury crashes on Bay Area highways have declined by 69% compared to the same week in 2019; statewide, the year-over-year decline was -57% as of May 4; DUI crashed declined by 35% (March through mid-May), and unsafe speed crashes were down 79% over the same period. Between early March and mid-May, injury crashes were down by 63% locally and 56% statewide. In contrast to the steep rise in speeding citations issued statewide as of mid-April, Bay Area Unsafe Speed Crashes declined by 79% between early-March and mid-May.
  • Air travel through San Francisco and Mineta San Jose International Airports combined have declined by 60% in March, 97% in April, and an estimated 96% in May; greenhouse gas emissions associated with the flights themselves (not airport-attributed emissions) could decline by an estimated 32% year-over-year here and 21 to 33% worldwide.
  • Annual greenhouse gas emissions could decline by an estimated 8% to 21% year-over-year, based on measured declines in vehicle miles traveled in March and April; global greenhouse gas emissions are expected to decrease by 4% to 8% percent this year due to the pandemic.
  • Overall air quality in Silicon Valley was improved to some extent between February and mid-May; however, changes in the regional Air Quality Index varied significantly between counties, and the extent to which they were affected by transportation-reductions is undetermined due to several factors. Reductions in fine particulate matter were more pronounced – down by 33% and 21% year-over-year, respectively, in April and the first half of May – likely resulting in greater regional visibility.

“Will the health crisis catalyze new approaches to transportation and a renewed emphasis on telecommuting?” queries Russell Hancock, President and CEO of Joint Venture, in the report’s Forward. “By quantifying the reductions and their associated impacts, we hope this study will inform the thinking on important questions such as these.”

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About the Silicon Valley Institute for Regional Studies

The Silicon Valley Institute for Regional Studies is the research arm of Joint Venture Silicon Valley, and is housed within the organization. The Institute provides research and analysis on a host of issues facing Silicon Valley’s economy and society. For more information, visit

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