OAKLAND — For trucking companies at the Port of Oakland, the hardest part is mostly over — if they’re still in business, that is.

A significant push that started in 2009 to transform smog-spewing diesel engines to ones that burn cleaner and capture pollutants before they enter the atmosphere has largely been completed. The costly effort forced trucking companies to change the way they do business, sometimes opting to upgrade or sell their entire fleet and lease trucks instead. Although regulatory agencies helped with early grants, it’s also forced smaller, owner-operator companies to retrofit their rigs or buy new ones, work for someone else or go out of business, several truck operators said.

“For us, it’s a good thing,” said Ben Soleimanieh, the operations manager for R&A Trucking Company. “These guys who had trucks that were 40 years old with the bumpers tied together, it took them out of the ballgame. These are the guys that were undercutting the rates and making it harder to compete.”

R&A Trucking Company operates 18 trucks, he said. The company bought all new vehicles when the new regulations were announced in 2008, and he said they replace them every 50,000 miles, ensuring the vehicles stay up to date with new emissions standards.

A recent spot check at the Port of Oakland, where the California Air Resources Board (CARB) set up an impromptu inspection checkpoint Wednesday, indicates the regulations appear to be working. Roughly a dozen vehicles zoomed through in the span of an hour with nary a snag. CARB Field Supervisor Shailendra Pratab said it has become increasingly rare to find vehicles that are not in compliance with the state’s emissions regulations, especially at the ports, where air quality standards are higher.

And, from an air quality perspective, that’s been a boon for both port workers and the surrounding community. In October, the port released its 2015 emissions inventory, showing a 98 percent reduction in diesel particulate matter, a 74 percent reduction in smog-producing nitrogen oxides and an 87 percent reduction in carbon monoxide, among other improvements — all from diesel engine trucks.

Not everyone is convinced those numbers tell the full story. Margaret Gordon, co-director of the West Oakland Environmental Indicators Project, an environmental advocacy nonprofit, questioned the port’s methodology, which used computer modeling as opposed to actual air quality samples.

“We have our own air modeling equipment, and we know we still have a lot of (particulate matter) in parts of West Oakland,” Gordon said.

Still, she admits she hasn’t had an asthma attack in the past two years. Her windows are not as gray-tinged and dusty as they have been in the past, and she isn’t seeing a lot of trucks idling on 7th Street anymore. But her nonprofit is also in the process of analyzing results from roughly 18 months of sampling the air quality levels to determine which hot spots remain. She’s also concerned about what will happen as the port continues to develop and attract more freight traffic, and said she wants to see a zero-emissions policy at the port.

Asking trucking companies to finance the cost of those emissions improvements has already been difficult for some operators. Kumar Gour, who manages the Oakland-based trucking company, Tighe Drayage, said the company used to operate three trucks before the regulations went into place. Now they operate two, and they were only able to make the conversion thanks to a $60,000 grant from the air resources board to buy new vehicles.

“That’s how we were able to make it work,” he said.

Ralph Warbington at Bay Area Port Services said his company, which operates five trucks, switched to leasing to ensure the trucks met all of the requirements, even as those requirements became more stringent over the years. It’s more expensive to lease, which means they are charging their customers more, a cost that is ultimately passed on to consumers, he said.

However, with fewer owner-operators now in business, it’s easier to compete, he said. The owner-operators were able to charge less since they don’t have to worry about workers’ compensation or other overhead involved with having employees.

“It was tough to be competitive,” Warbington said. “The rates were repressed for quite a while. Now, they are more in line with what we need to cover the cost of the trucks.”

He continued, “Now that there are less owner-operators, and everyone has compliant trucks, the playing field is a lot leveler.”