LOS ANGELES -- Coronavirus stay-at-home orders that went into effect on March 20 have reduced vehicle collisions on California roadways by roughly half, according to a UC Davis survey that is the first to estimate the impact of the extraordinary health orders on traffic.
"The reduction works out to about 15,000 fewer collisions per month and 6,000 fewer injury accidents per month," said Fraser Shilling, co-director of the Road Ecology Center at UC Davis. Shilling said the reduction in motor vehicle accidents on highways and roads, "can be directly or indirectly attributed to the shelter-in-place order."
The survey suggests that a 60% drop in traffic volume -- when compared to the same period last year -- accounts for a roughly 50% decline in collisions on roadways policed by California Highway Patrol.
As people have limited their vehicular use to traveling to work and obtaining food and other essentials, it was predictable that collisions would decrease. And with bars and restaurants shuttered, there would be even fewer drunk driving accidents.
But Shilling was surprised by the extent of the reduction.
"We've never had a statewide experiment like this before," he said, "where you severely reduced traffic and then in real time monitor the public health implications of less vehicles and their pollution."
He said it is unlikely, however, that shelter-in-place orders in California and across the nation would result in fewer deaths from traffic accidents than the number of lives claimed by the coronavirus.
Susan Handy, a professor of environmental science and director of the National Center for Sustainable Transportation at UC Davis, described Shilling's findings as "an important reminder of how hazardous our normal lives have become."
Using data derived from California Highway Patrol incident reports, the survey compared the average daily number of collisions on state highways and roads between March 10 and 19, 2019 and March 21 and 30, 2019 with those reported during the same periods in 2020.
The average daily number of collisions reported in the 10 days prior to the stay-at-home order was 1,116, compared with 500 per day after the order was issued by Gov. Gavin Newsom.