DRIVING • Biggest decline — 90% — seen in Washington, D.C.

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While the 75 percent drop in California was dramatic, seven states recorded decreases of 80 percent or more in the report. The District of Columbia accounted for the biggest decline, 90 percent.

Arkansas reported the smallest reduction in miles driven at 60 percent.

“It was a little bit surprising to see that we here in California were not at the top of the list,” Shilling said in a telephone interview. “It’s hard in some cities like (San Diego) and Los Angeles to do the things you need to do without a car, without driving. They’re not really set up, compared to some of the states with good transit systems or that have more compact cities.”

New York, New Jersey, Connecticut and Massachusetts — home to big cities with extensive subway, bus and train systems — each saw reductions of more than 80 percent. Michigan, one of the states hardest hit by the outbreak, reported an 82 percent drop in miles driven.

The UC Davis study said the reductions led to proportional decreases in greenhouse gas emissions spewing from vehicles.

Using average fuel mileage rates for cars and trucks, the report estimated carbon dioxide emissions in the U.S. fell from 44 million metric tons in the first week of March to 12 million metric tons in the second week of April, a reduction of about 72 percent.

California’s emissions dropped about 75 percent in the same period.

State policymakers have set a target to reduce greenhouse gas emissions 80 percent from 1990 levels by 2050. The report extrapolated that if traffic remained 75 percent lower for one year, California could meet half of its 2050 climate change target.

“It’s really a theoretical exercise,” Shilling said, acknowledging the number of miles driven will go back up as public health restrictions are lifted. “I’m just projecting forward and saying, if we keep doing this reduced driving, this will be the benefit of doing that.”

According to the California Air Resources Board, 41 percent of greenhouse gas emissions in the state in 2017 came from the transportation sector. Nationally, transportation accounts for 29 percent of emissions.

Less driving means fewer trips to the gas station and that means a decrease in state tax revenue collected at the pump. California has the highest gasoline tax burden per gallon than any other state, according to the American Petroleum Institute.

The UC Davis study estimated gasoline sales tax revenue dropped $161 million a week during the shutdown, or $1.3 billion less than would have been collected before the outbreak. That figure includes money generated by the passage of 2017’s Senate Bill 1, the controversial legislation that increased the gas tax by 17.6 cents per gallon that supporters promised will go directly to road repair, transportation and safety projects.

Reductions in revenue may likely lead to some difficult decisions by the Legislature, Caltrans and state’s Department of Finance, Shilling said.

“I’m sure there’s going to be a lot of jostling of elbows to decide who’s going to be at the front of that line for that smaller piece of the pie,” he said.

Once the worst of the pandemic is over, will old driving habits resume and demand for gasoline return to previous levels?

Shilling suspects more employees will work from home, for at least part of their regular work weeks.

“I think everybody’s going to think of things a little bit differently,” he said. “And I think it will affect how much we drive and therefore affect how much fuel we use ... This is a time of incredible change and I think it’s also an opportunity.”

rob.nikolewski@sduniontribune.com (619) 293-1251

Twitter: @robnikolewski