Wizardry That Keeps the City in Motion

Red light.

You drive up to one of the 4,000 intersections in Los Angeles equipped with a detector embedded in the pavement. It’s supposed to let the traffic light know you are there.

You wait patiently.

It’s taking too long.

To make the light go green, do you:

a) Drive back and forth to fool the detector into believing there are several cars waiting?

b) Bounce up and down in your seat to make the car feel heavier?

c) Do your nails and/or check your hair in the mirror?

The correct answer is: none of the above, although you might as well pick “c” because despite widespread myths to the contrary, there is nothing you can do to make the light turn faster. In fact, one of the above answers can actually make your wait longer.

“We hear all kinds of things about what people believe about traffic detectors, and almost all of them are wrong,” said transportation engineer Brian Gallagher, who runs the incredibly complex, mostly hidden and generally misunderstood system of traffic detectors without which the city’s legendary traffic jams would likely be even worse.

Low-tech detectors--usually just a few loops of wire embedded in the pavement--have been aiding the flow of traffic for decades.

But low-tech alone just won’t make it in Los Angeles, king city of America’s car culture and home to perhaps the most diverse population in the nation, which meets daily on the roadways.

So city engineers are deploying an arsenal of smart weapons in the traffic war. Only here are there detectors specifically designed to deal with wheelchair users, bicyclists, firetrucks, blind people, horses, buses, commuter trains and Orthodox Jews.

Red light.

Orthodox Jews?

According to their beliefs, strict Orthodox Jews are not allowed to do any work on the Sabbath--sundown Friday to sundown Saturday. That includes using any mechanical devices.

“They can’t push the ‘Walk’ button,” Gallagher said.

So, in areas near synagogues that have controlled traffic signals, congregants were getting stuck at intersections, waiting in vain for a walk signal. Rabbis were calling upon city officials to “Let my people go,” and it was up to Gallagher’s department to figure out a way how.

It’s just one example of how traffic detectors have been used to address numerous transportation problems in this city whose roadways are its lifelines.

Green light.

When Traffic Slows to a Crawl

Watch out for that man crawling across the intersection.

It’s afternoon rush hour downtown. Gallagher waited for the “Walk” signal at the intersection of San Pedro and Temple streets. Then the sultan of signals began crawling, slowly, across Temple.

While it’s no surprise that a traffic engineer for the city of Los Angeles might be suicidal, Gallagher was in no danger of doing himself in. He was just showing off.

This is the test site of one of the newest traffic control regimens--a microwave radar unit adapted to detect pedestrians. It was placed here, near a major Veterans Affairs medical clinic, because this intersection is regularly used by disabled people and seniors who might not be able to make it to safety in the usual, state-mandated minimum of one second for every four feet of crosswalk.

The detector, mounted on a utility pole, is set to sense if there is a person in the crosswalk at the point the light normally would change. If there is, the light is held until the pedestrian, even at crawling pace, makes it to the sidewalk.

“We’ll try anything if we think it might work,” said Gallagher, dusting himself off.

(Don’t try the crawling experiment on your own--since Gallagher’s demonstration, the unit was set to allow a maximum of only nine extra seconds).

Similar infrared systems are being tested at two Northridge intersections--Nordhoff Street and Lindley Avenue, and Plummer Street and Zelzah Avenue.

In the northern Los Angeles County city of Lancaster, traffic engineers are making use of an even more high-tech system--video imaging. Typically employing four video cameras per intersection, it trips a sensing device whenever a vehicle enters the video field.

“If the street is widened, or utility equipment is added, we don’t have to dig up or otherwise relocate a unit,” said Bob Weithofer, traffic engineering manager for the city, which is using the system at 35 intersections. “We just download new instructions to the controller, and that’s it. Takes just a few minutes.”

In Los Angeles, traffic engineers are adapting the microwave units to a variety of uses, including what is probably the world’s first horse detector, installed in July on an equestrian path in Griffith Park near an intersection with a bike path. To avoid horse-bike collisions, the detector sets off flashing warning signs on the bike path when it senses an approaching horse.

The unit is positioned so that it detects something as tall as a horse and rider, while ignoring smaller animals, Gallagher said.

Microwave units were installed at a non-signal intersection in Sun Valley this month to detect pedestrians in the crosswalk. The intersection of Lankershim Boulevard and Arminta Street was the site of a hit-and-run accident in October that left a woman and young child critically injured.

In this so-called smart crosswalk, the detector sets off a flashing yellow light to warn drivers that pedestrians are present.

A second smart crosswalk is planned for an intersection in Highland Park that has been the scene of several accidents.

Finally, microwave is also Gallagher’s detector of choice to help Orthodox Jews stranded at intersections. The current solution is to simply program the traffic signals near Orthodox synagogues to automatically provide walk times during every cycle in the 24-hour Sabbath period--inefficiently halting traffic even when no pedestrians are present.

Rabbi Nachman Mandel, who teaches at the Jewish Learning Exchange school in the Fairfax area, has worked with the traffic department to determine which intersections needed Sabbath treatment.

“Once I was talking to one of their men working on a signal,” Mandel said, “and he used the term ‘Sabbath clock.’ That is the same expression we Jewish people use in our homes to refer to a device that automatically turns things off and on on Saturday.

“I was very impressed how much they had researched this.”

Gallagher wants to use the microwave units to determine exactly when pedestrians are waiting for the walk signal.

At first, Mandel thought that was a great idea. “It’s fantastic, unbelievable what technology can do these days,” he said. But then, on reflection, he said it might violate Sabbath rules.

“It may create a problem. We are not allowed to cause an electronic object, like the door to a supermarket, to be activated by our actions.”

Gallagher said he was leaving it to a company that sells microwave units to look into any religious conflicts. He knows there might be some criticism of the transportation department spending resources to make special arrangements for a religious group.

“To us it’s an accessibility issue,” he said. “If we don’t do something, we end up with safety problems.”

Another project involves finding an efficient way to empower firetrucks and other emergency vehicles to turn signal lights green as they approach intersections. Currently being tested is a system that uses sensors designed to recognize the sonic frequency patterns of emergency vehicle sirens.

In the meantime, the city is working on the development of a hand-held transmitter that emergency vehicle drivers can use to command a traffic light to turn green as they approach.

The city did test optical sensors that were to respond to flashing lights on emergency vehicles. It didn’t work well, but started a rumor among motorists that flashing a car’s headlights would cause a traffic signal to change.

“No way,” Gallagher said, shaking his head. “We’re not that dumb.”

These new devices represent the cutting edge. But the workhorse of traffic detection remains the lowly wire-loop detector embedded in the pavement and charged with a low dose of electricity. That loop is what is found beneath the circular cuts into the pavement at thousands of intersections.

The current generates an electromagnetic field. Metal passing overhead absorbs some of the energy, indicating that a vehicle is present.

The loop detectors began appearing in the early 1960s, after decades of experimentation with other devices all aimed at the same basic dilemma: keeping traffic on a main road flowing with as little interruption as possible from less busy side streets.

The first attempt, according to the Institute of Transportation Engineers, came in 1928 when a device invented by a man named Charlie Adler made its debut at a Baltimore intersection.

“Adler’s Horn,” as it was called, was attached to a utility pole next to a sign that instructed: “Sound Horn to Clear Signal.” Its sensor picked up the sound of a horn and gave the honker a green light.

Although “Adler’s Horn” was not popular in the neighborhood for obvious reasons, it stayed in service for several years, followed by other devices: pressure-sensitive units triggered by the weight of a car, magnetic detectors and photoelectric cells.

All had operational drawbacks--they missed vehicles, made false calls and were affected by weather.

The electromagnetic loop used today is far more reliable and cheaper--”the heart of the system,” Gallagher said.

It’s not hard to tell where the loops are located--the pavement cuts can be easily spotted. Road loops are usually 6 feet wide, although smaller ones are used for special purposes, such as detecting wheelchairs on sidewalks at intersections frequented by disabled people. Despite being called loops, they are sometimes rectangular or other shapes. Newer ones are indeed circular, but octagon-shaped ones are still in use.

Driving onto a loop doesn’t turn the traffic signal green right away. An electronic brain, located in a nearby metal box, checks only at certain times--usually about once a minute--to see if the detector has been tripped. If it has, a sequence begins that results in a green light.

So, if you drive onto the loop just before the detector is checked, you’ll get a green light quickly. If you drive onto it right after the check is done, you have to wait an extra minute or so.

That’s why rolling backward and forward doesn’t help--and indeed may hinder.

“Just as you roll backward out of the detection zone,” Gallagher said, “the decision time might come. The signal would think there is no car there, and by the time you get back into the zone, it’s too late and you have to wait for the next time.”

Motorcycles can trip a loop detector, but there is a trick to it.

“The signal from the wire is weakest right down the middle of the detector,” Gallagher said. “If you are on a motorcycle, it’s a good idea to stop right on the wire mark on the outside of the circle. That’s where it will pick you up.

“And if you lean the bike over in the direction of the detector a bit, it increases the surface area of metal to be detected.”

Command Post for L.A. Traffic

In an underground, temperature-sensitive compound several floors beneath City Hall, the high- and low-tech of the traffic detector worlds meet. This is the Automated Traffic Surveillance and Control Center, known as ATSAC, that went into operation just before the 1984 Summer Olympics.

With its huge video screens and desktop terminals, it’s a war room, the command post for the war on L.A. traffic. Nearby, rows of mainframe computers silently process traffic information and send instructions to 2,000 intersections--about half those with loop detectors.

Engineers peered up at one of the screens showing a live abstract representation of the intersection at Long Beach Avenue and Washington Boulevard.

Flashing circles--which changed color whenever a car stopped at or drove through the intersection--showed the location of the loop detectors.

On the adjacent screen was a live video shot of the same intersection. ATSAC can get a picture from any of 160 high-powered cameras placed above key intersections. Drivers and pedestrians could be seen going about their business, probably unaware that they were being watched in a room beneath City Hall.

This intersection is notable because a Metro line runs through it. The trains have their own loop detectors beneath the tracks.

Transportation engineer Sean Skehan called a train’s approach like a sports announcer.

“The train is coming, and [he paused for the detector light to come on] we detect it! Now, it will get a green [another pause] and the train is on it’s way.”

Skehan smiled. “This is a real exciting place to watch trains,” he said, sincerely.

“Mass transit gets priority,” Gallagher said, explaining why the train got a quick green light.

That includes buses. But how to distinguish a bus from other vehicles with just a loop of wire? Skehan solved the problem by using two loops a set distance apart, which can determine the length of a vehicle passing above.

Because MTA buses come in only three lengths--30, 35 and 40 feet--a green arrow of especially long duration is triggered when the loops--now being tested at two downtown intersections--detect something in those sizes. Skehan used a similar approach to make a bicycle detector. The first, on a bike lane along Forest Lawn Drive in the San Fernando Valley, has been declared a success. About 20 more are scheduled to be installed this year.

The most adventurous role yet for loops is their partnership with ATSAC computers to make traffic decisions without human intervention, a system in use in several heavily trafficked areas, such as Los Angeles International Airport, Dodger Stadium, the Hollywood Bowl, parts of Ventura Boulevard and in Westwood.

Around Dodger Stadium, “we used the loops to gather data about the traffic pattern created when a game lets out,” Gallagher said. “Then we set the computers to recognize that pattern. When they do, they automatically switch over to an ‘after-game’ mode, favoring traffic moving away from the stadium.

“We don’t have to guess when a concert is going to get out anymore and program that in,” Gallagher said. “The loops recognize what’s happening and do it on their own.”

A driver’s dream: Detectors that know when to get out of the way.