If the Orange County Transportation Authority doesn't widen the San Diego (405) Freeway in Costa Mesa, an existing bottleneck could relocate from Fountain Valley to Costa Mesa, transportation officials said Tuesday.

In his update to the Costa Mesa City Council about OCTA's three scenarios to improve the 405, project manager Niall Barrett said extending the project into the section south of Euclid Street onto the Corona del Mar (73) Freeway is the best option to manage congestion.

If the proposed widening beginning at the San Gabriel (605) Freeway stops at Euclid in Fountain Valley, as outlined in one scenario, the bottleneck will shift to Costa Mesa, Barrett said.

"We can't build our way out of the problem on the 405," he said. "It's congestion management."

OCTA is looking to widen the freeway — Southern California's busiest — either one or two lanes in each direction between the 605 to the north and either Euclid or the 73 to the south.

But tens of millions of dollars and a decade after widening the Costa Mesa section of the 405 — and only three years after revamping the Fairview Road overpass — some residents aren't keen on the idea.

"We deserve better. We did our part," said Councilman Gary Monahan. "The issues are not in Costa Mesa. This is not going to help our traffic."

The option proposed Tuesday would affect Costa Mesa the most. It would require tearing down and widening the Fairview bridge over about 18 months, cutting off the crossing for a brief window, OCTA officials said.

A second carpool lane doubling as a toll road would link the 73 to the 405. While this option is about $300 million more than two others being considered, it's also the only revenue generator. Similar to what's on the Riverside (91) Freeway, a toll road option would charge solo drivers to use the dedicated lane.

The job wouldn't require moving the freeway closer to north Costa Mesa homes, according to OCTA.

OCTA is expected to release its environmental impact report on the three widening options later this month and will host three public meetings in the coming months.

joseph.serna@latimes.com

Twitter: @JosephSerna