LOS ANGELES — To combat its infamous traffic, Los Angeles has built subways and light rail lines. It has widened highways and added car pool, toll and bus-only lanes. But the roads have remained stubbornly clogged, creating a drag on commerce and the quality of life that has persisted here for generations.

Now, in the latest ambitious and costly assault on gridlock, Los Angeles has synchronized every one of its 4,500 traffic signals across 469 square miles — the first major metropolis in the world to do so, officials said — raising the almost fantastical prospect, in theory, of driving Western Avenue from the Hollywood Hills to the San Pedro waterfront without stopping once.

But with the number of cars on the road here continuing to rise (and almost seven million commuters already on the road each day during the rush in the metro area), even the system’s boosters admit that it may not be enough to prevent gridlock from growing worse. The average time commuters waste in traffic has climbed since 2008, according to the Texas A&M Transportation Institute’s annual urban mobility report from 2012, and the latest improvements may ultimately do little more than slow congestion, rather than reverse it.

Built up over 30 years at a cost of $400 million and completed only several weeks ago, the Automated Traffic Surveillance and Control system, as it is officially known, offers Los Angeles one of the world’s most comprehensive systems for mitigating traffic.