“I doubt the project would have been undertaken in the first place if we’d known it would cost $1.6 billion,” said Mr. Yaroslavsky, whose district includes the Sepulveda Pass. “There’s a lot of bad taste in my mouth about this. There were mistakes made all around. It was a nightmare of a project.”

Transit officials were quick to defend the 405 project, saying it was an essential part of a crucial campaign to expand the transportation network in a city notorious for traffic congestion. It was extraordinarily complicated, they said, because the highway remained open while the work continued, and contractors had to grapple with moving hundreds of miles of utility pipes and lines discovered only after ground was broken.

“It really did improve the traffic conditions on the 405,” Phillip A. Washington, the head of the transportation authority, said. “Added capacity. Made the freeway safer. Traffic would have been much worse if we had not done anything.”

Still, the price was high — in inconvenience as well as dollars.

And on two occasions it stopped much of Los Angeles cold. For nearly an entire weekend on two occasions, in 2011 and 2012, the Metropolitan Transportation Authority closed down a 10-mile stretch of the 405. It was one of the more aggravating chapters of the project connecting the Los Angeles basin with the San Fernando Valley.

Bob Anderson, an engineer from Sherman Oaks who was on the community advisory board for the project, said his neighborhood was disrupted for nearly five years. And with the construction over, now all he sees are long lines of cars trying to enter or exit the highway.

“As far as improvement, I don’t see anything,” Mr. Anderson said. “Was it worth a billion dollars? I doubt it. Was it worth $1.6 billion?”