The first patented electric traffic signal went into operation 100 years ago. PostTV looks into how a modern traffic signal system keeps traffic flowing—or not—in a busy city like Washington, D.C. (Jason Aldag/The Washington Post)

Commuters’ lives are ruled by clocks and traffic signals. They don’t know whom to blame for the former, but they can narrow the candidates for the latter.

Tuesday is the 100th anniversary of the installation in Cleveland, Ohio, of an electric traffic signal system, for which James B. Hoge received a patent in 1918. The system’s separate units displayed red and green lights to control the flow of traffic coming from four directions into the intersection of Euclid Avenue and East 105th Street.

Like so many life-altering innovations, the traffic signal has several claimants to parenthood. In 1912, Salt Lake City traffic stopped and moved in response to a red-green signal developed by a policeman named Lester Wire, who did not patent the device. In 1923, inventor Garrett Morgan patented a cross-like device that added a third status, something between stop and go that would give drivers warning that the signal was changing.

From such origins, efforts at controlling our behavior in traffic have become more sophisticated. The early versions still needed an officer at the intersection to manually control the devices. They not only acquired automatic timers but also became interconnected. Today, hundreds of individual signals can be linked to central computers and coordinated, though many travelers would scoff at the notion that any local government does this successfully.

The reason signal timing and coordination are so important to traffic engineers is that they don’t see much chance of adding to the road network. They need to get more efficiency out of the roads we have. If they can match the traffic signals to the traffic flow, people get where they’re going quicker and safer, and they burn less gas.

Signal timing and coordination are important to drivers because they don’t look at traffic the same way engineers do. Drivers don’t see a road network. They see a line from Point A to Point B. It’s the line they follow to and from work. Give them a few more seconds of green at the intersection where they get stuck every day and, in their minds, you’ve solved our transportation crisis.

When I share travelers’ complaints about traffic signals, I usually get one of two reactions from traffic engineers. They may say thanks for bringing it to our attention, and we’ll take a look.

Or they may sigh and explain to me that they’re not gods. They can add and subtract seconds for the different directions at an intersection. But they can’t manufacture time. If there are going to be winners at an intersection, there also are going to be losers.

Everybody wants to be the winner. But at some intersections in congested urban areas, there are going to be many, many losers when the engineers start removing those precious seconds.

That’s not to let the engineers off the hook. Transportation planners say that signal timings should be checked every three years. A study for the regional Transportation Planning Board for the years 2009-2012 found that nearly a quarter of the D.C. region’s 5,500 signals had not been checked during that time period.

On the other hand, three-quarters of the signals were checked and, as the traffic engineers say, “optimized.” But that may not mean what a driver thinks it means. To the engineers, an optimized system doesn’t mean that every driver encounters a minimum of delay. They’re going for the greater good. And in that process, you may be asked to sacrifice for the sake of drivers or pedestrians who at this second are blocks away.

That’s how time and traffic come together in the continuing history of the signals. Time is relative to where you’re sitting in traffic.