The new carpool lane on the northbound 405 Freeway between the 10 and the 101 opened at about 4:30 a.m. Friday, according to Metro.
The grand opening comes five months ahead of schedule — and just in time for the Memorial Day travel weekend.
"It's going to give people with multiple passengers the ability to ride in a dedicated [lane]," said Metro spokesman Dave Sotero. "And that will help improve the efficiency of the entire freeway and keep traffic moving."
The new carpool lane between the 10 and 101 freeways was part of a $1 billion improvement project.
Three freeway bridges were re-built, overpasses were widened and portions of Sepulveda Boulevard were also re-surfaced as part of that project.
This story has been updated and was originally published on Thursday, May 21.