Accident hotspots have cooled off under lockdown, with thousands of lives saved (charts: UC Davis)

Unique data shows Californian road carnage has halved since the state’s Covid-19 lockdowns, with over 4,600 people saved from death or life-changing injury during 22 days of lockdown, saving the state over US$1 billion (HK$7.8 billion) in costs.

Researchers say the lockdowns are the first time in modern history they can analyse links between traffic volumes and road crashes. “There is no equivalent in our recent transportation history to such large changes in vehicle movement on our state and local roads,” says a study led by Fraser Shilling, Co-Director of the Road Ecology Center at UC Davis.

Real-time traffic flow measurements, together with detailed reports from California Highway Patrol and hospital reporting showed not only a reduction in fatal collisions, but a 50% decrease in hospital trauma injury incidents reported by pedestrians and cyclists.

Contrasting with anecdotal reports of drivers using the emptier roads to race and speed, Shilling says the study found average speeds on highways only 1-4 mph (1.6-6.4 kph) above normal, and peak speeds only 1-3 mph (1.6 – 4.8 kph) higher. But while speeds are up only a little, two days of heavy rainfall revealed the multiplier effect of speed on wet surfaces – crashes were up fivefold on those two days, against an average of 2 to 3 times on an average rainy day before the lockdowns.