Nobody likes a pandemic.
But if there's a silver lining to the coronavirus pandemic — and the state-ordered lockdown that followed — it may be a marked improvement in air quality residents enjoyed in the San Joaquin Valley.
"During the early days of the pandemic, a lot of people were sheltering in place, working remotely and not commuting to work," said John Liu, Caltrans District 6’s deputy director for maintenance and operations.
"There was a very large reduction in traffic volume on almost all the highways," he said.
Highway 99, the busiest traffic artery in Bakersfield and the major north-south corridor on the eastern side of the valley, experienced a stunning phenomenon as traffic volume plummeted.
According to Jessica Olsen, program manager for the San Joaquin Valley Air Pollution Control District, an analysis of vehicle miles traveled on the valley portion of Highway 99 showed an estimated 45 percent reduction in April, compared with the same month last year.
Even commercial truck traffic in the valley took a hit, with trucks on Highway 99 logging some 26 percent fewer miles in April 2020 than they did in April 2019, Olsen said. And with trucks being among the biggest polluters in the valley's troubled air basin, the reduction in total miles translated to a reduction in pollutants that cause ground-level ozone. The main ingredient in smog, ozone can trigger a variety of health problems, particularly for children, the elderly and those who suffer from asthma and other lung ailments.
"There are thousands of sensors along the freeway system that provide real-time data," Olsen said of the technology used by Caltrans to gather traffic-related data.
The steep drop in vehicle miles traveled in April coincided with a 22 percent drop in valley ozone levels as compared with the previous five-year average, Olsen said.
That's a good thing, she said, but also cautioned against attributing the improvement in air quality exclusively to the reduction in traffic.
Air quality in the valley has been improving for years, she said.
"Last year was our best ozone year on record," Olsen said. "This year is shaping up to be a great year as well, assuming we aren't inundated by outside influences like wildfires."
By May, traffic numbers on Highway 99 were already beginning to trend upward. But they still remained well below normal.
The air district estimated a 20 percent reduction in total vehicle miles traveled last month along the valley portion of 99, with commercial trucks showing a 16 percent drop in miles traveled, compared with May of last year.
Air officials saw a corresponding reduction in ozone pollutants — a 13 percent dip.
Traffic counts on Interstate 5, north of the junction of Highway 99, also showed lower total traffic volumes, and the reductions appeared to be even more dramatic than those seen on Highway 99. Truck traffic, however, was the exception, with 99 experiencing a larger reduction in commercial truck volume.
According to data collected by Caltrans on the Interstate 5, total traffic volume — a different measure than vehicle miles traveled — decreased by 19.7 percent in March, 48 percent in April, and 38 percent in May, compared with the same months last year. The corresponding decrease in the volume of truck traffic was much more modest at 1.1 percent, 9.8 percent and 4.9 percent, respectively.
On Highway 99, between I-5 and Highway 46, the drop in total traffic volume was likely more relevant to air quality in metro Bakersfield.
Total traffic volume on this stretch decreased by 18.9 percent in March, 40 percent in April, and 24.4 percent in May, Caltrans found. The corresponding drop in truck traffic was 4.1 percent, 11.3 percent, and 8.3 percent, respectively.
It's clear that a significant decrease in traffic volume and vehicle miles can have a positive effect on the valley's air quality.
That means the opposite is also true. The miles we drive, and don't drive, clearly makes a difference in the air we breathe.
Ironically, the air district has no direct jurisdiction over mobile sources of air pollution, such as cars, commercial trucks, trains and buses. Yet, mobile sources contribute the largest portion of emissions, by far — emissions that generate much of the ozone smog and particulate pollution that continues to bedevil the valley to this day.