I noted the synchronization of all Los Angeles traffic lights a while back but a new piece in the New York Times describes how much time the new system is supposed to save drivers:

The system uses magnetic sensors in the road that measure the flow of traffic, hundreds of cameras and a centralized computer system that makes constant adjustments to keep cars moving as smoothly as possible. The city’s Transportation Department says the average speed of traffic across the city is 16 percent faster under the system, with delays at major intersections down 12 percent.

Without synchronization, it takes an average of 20 minutes to drive five miles on Los Angeles streets; with synchronization, it has fallen to 17.2 minutes, the city says. And the average speed on the city’s streets is now 17.3 miles per hour, up from 15 m.p.h. without synchronized lights.

Mayor Antonio R. Villaraigosa, who pledged to complete the system in his 2005 campaign, now presents it as a significant accomplishment as his two terms in office comes to an end in June. He argued that the system would also cut carbon emissions by reducing the number of times cars stop and start…

“If we reduce average travel time in Los Angeles by 20 percent, then we will see more people traveling,” Professor Moore said. “It’s money well spent, but part of the benefit is not speed, but throughput.”

These seem small fairly small changes, a few minutes for each average trip, but these would add up over time for individual drivers. Additionally, small improvements in a complex system like LA traffic could have very beneficial outcomes for the whole system.

But, as the article notes, these reduced times may not last long because more people want to drive. This is a rule of road construction: if you add lanes or improve traffic flow, more people will likely get on the road, limiting the benefits of changes. Sychronization of traffic lights may speed things up but there are larger issues at hand including the number of cars on the road and too much reliance on streets and highways to get people where they need to go.