Question of the Day - 18 March 2019

We get this question fairly frequently. We wonder about it ourselves often, sitting seemingly forever at red lights where there’s no cross traffic or approaching green lights from blocks away that don’t change before we breeze right through. So we finally determined to track down the way traffic lights in Las Vegas work — or don’t, as the case may be.

When traffic lights are operated primarily by sensors — video detection, magnetic loops embedded in the road’s pavement, infrared technology, and others — it’s fairly obvious why they change when they do. Sensors detect vehicle flow and the lights respond to cars rolling over, under, or past them. Green lights are longer when, for example, eastbound and westbound cars keep approaching an intersection. Red lights are shorter when only a few north-south cars pass through the green at the same intersection. We’ve all seen variations on this a million times.

But when lights are operated primarily by timers, it’s also fairly apparent — sometimes not in a good way.

Vegas traffic lights, nearly 2,000 of them, are pre-programmed and controlled by a central computer at the Regional Transportation Commission’s Traffic Management Center. The programming changes according to several variables: time of day, day of week, and travel demand at intersections, among others. So if the timing is off for one reason or another, one direction gets a free pass, while drivers in the other direction sit, and sit, and sit, getting frustrated.

For example, in the wee hours (midnight to 5 a.m.), according to the RTC, traffic signals operate based on vehicle detection. But if the signals don’t get that message and remain timed for regular traffic hours, there you are at 3:30 in the morning, waiting alone at a red light, with no other cars to be seen, wondering if the light is “stuck,” feeling foolish and impatient, seriously considering running the damn thing, and — admit it — actually doing so on occasion.

Timing can also be affected by pedestrians activating the Walk signal (which generally provides an extended green light for vehicles traveling in the same direction) and the approach of emergency-response vehicles (equipped with special transmitters that communicate with traffic signals, allowing for green lights as first responders approach intersections).

In Las Vegas, the Strip is also a good example of timing that marches to a different beat. On the Boulevard, you crawl from one red light to the next at any time of day. It’s rare enough to hit a green light and a miracle to pass through two in a row. Lights on the Strip are timed to prioritize traffic entering and exiting the casinos (though at least one conspiracy lover of our acquaintance swears that entering the casinos gets much more green-light time than leaving); they also take into account the herds and hordes of pedestrians continually crossing the Strip entrances and holding up traffic.

Another QoD correspondent with advance access to this question notes that the signals at the intersection of the Strip and Flamingo Rd., for example, seem to be timed for a minute or more in all four directions, which includes left turns. So if you're driving east on Flamingo and reach the signal at the Strip just as it turns red, you have to wait for four minutes or longer for the lights to time back in your direction. We're sure many of you have other examples, but Flamingo and Strip is one of the worst.

Bottom line: Generally speaking, when it comes to traffic lights, sensors are less crazy-making than timers and Las Vegas signals are for the most part timed.