A new kind of freeway interchange is coming to California — possibly to Berkeley, in time — and it’s likely to make drivers scratch their heads in confusion.

It’s called a diverging diamond. To enter the freeway, the cutting-edge interchange requires drivers to veer at a 45-degree angle across the center divide, switching sides with opposing traffic and briefly motoring across as if they are in England.

By being on the left side, they can then glide left onto the highway without a dangerous 90-degree turn across oncoming cars.

Transportation officials broke ground on the state’s first diverging diamond interchange late last month where Union Road crosses Highway 120 in Manteca (San Joaquin County). The interchange is not scheduled to open until fall 2020, but the design’s popularity is spreading.

At least two more diverging diamonds are planned in the Central Valley, and engineers are considering the design for the reconstruction of the Ashby Avenue interchange over busy Interstate 80 in Berkeley.

Some traffic planners are smitten with the concept and how, in the name of efficiency and safety, it forces opposing traffic to negotiate an X-shaped, signalized crossover before a bridge or underpass. As freeway-bound drivers drift to the left to an on-ramp, those heading through the interchange to the other side of the freeway follow the road back to the right at another crossover.

Still, for the general public, looking at diagrams, video simulations and overhead photos can yield more amazement than clarity. What is ultimately required is the experience.

“If you have never driven one before or navigated one, it looks confusing,” said Matt Brogan, of the Mark Thomas firm that designed the Manteca interchange. “But once you’ve driven one, it makes sense.”

Koosun Kim, Manteca’s deputy public works director, said he made his maiden voyage through a diverging diamond interchange, or DDI, at the nearest one to California — on Highway 395 in Reno. Drivers, he promised, only need to follow the signs and the traffic ahead to get the hang of it.

“A lot of people don’t even know they’ve gone through the DDI,” Kim said. “They say, hey, we passed it.”

Despite the unorthodox approach, proponents say, diverging diamond interchanges offer obvious appeal: They save money, time and collisions. Most of the interchanges are expansions, requiring less land and shaving construction costs associated with pricey new overpasses needed for widening projects.

“The big key for the city was that the cost was a lot lower,” Brogan said.

The $26 million price tag is about $10 million less than the cost of widening a traditional interchange, Kim said.

No diverging diamond interchanges are planned in the Bay Area, but Caltrans spokeswoman Lindsey Hart said the concept is among those being considered for Ashby Avenue in Berkeley, where environmental studies and planning for a new I-80 interchange have begun.

“These are new to California,” she said. “At this point, it’s just an idea for Ashby.”

While new to California, diverging diamonds have become an increasingly common choice in other states, where about 120 are either in use, under construction or in design, said Gilbert Chlewicki, director of Advanced Transportation Solutions and the creator of the interchange design.

A study last year of 26 such interchanges in 11 states showed a 37% decline in collisions and a 54% drop in major crashes causing death or serious injuries.

While driving in the opposite direction might seem to invite hazard, the newfangled interchanges have fewer “conflict points,” where vehicles traveling in different directions could slam into each other, traffic experts said. Vehicles turning left through traffic notoriously collide with those moving straight ahead.

But some pedestrians and bicyclists complain about the design. In Manteca, city officials circumnavigated that problem — literally — by building a separate bike and pedestrian path that skirts the interchange.

Chlewicki, the “father of the diverging diamond interchange,” created it for a term paper at the University of Maryland in 2000. The first was built in Springfield, Mo., in 2009.

“Every state that has put one in is trying to put more in,” Chlewicki said. “They see the advantage safetywise and costwise. It is very, very cost-effective.”

But will it catch on across California?

“Absolutely,” said Brogan, who’s already working on more diverging diamond interchange designs.

Some Central Valley locales, including Mountain House (San Joaquin County), Modesto and Ceres (Stanislaus County), will see diverging diamonds in the future, transportation officials said. Manteca is considering adding two, Kim said.

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan