Gardena Hopes Computer Will Fine-Tune Its Traffic Lights, Unclog Its Streets

Far away from the cars crawling through rush hour in Gardena, a computer quietly tracks the vehicle flow on city streets, changing traffic lights from red to green to ease a tightening bottleneck.

That’s how city officials describe the way traffic problems will be handled when Gardena’s $2.35-million traffic signal system goes into operation next year.

Using federal grant funds, Gardena has completed blueprints for the system, which city officials boast will rival any other in the state. Installation will begin this fall and take six months to a year to complete, city Public Works Director Ken Ayers said.

Travel time across the city should be cut 12% to 14% once the system is installed and the computer program is fine-tuned, said John Tsiknas, project manager at Frederic Harris Inc., a national traffic consulting firm that worked with the city to design the system.

Sensors in the pavement at every intersection with a traffic light will feed information on car flow to a central computer in the Public Works building. The computer will check that information every minute and, if necessary, make individual timing corrections to 52 signals throughout the five-square-mile city.

The federal grant was awarded to ease congestion on local streets, which in Gardena are jammed by commuters going to and from the Harbor and San Diego freeways. At peak hours, about 80% of city traffic is made up of commuters who live and work elsewhere, said Woody Natsuhara, Gardena’s engineering superintendent.

The system will be the first “traffic-responsive” centralized computer system in the South Bay, Los Angeles County officials said.

Other cities in the county and elsewhere in California have started to use computers that control signals, they said, but many of these systems do not respond to traffic-flow information and are used instead to set standard timing sequences and detect signal malfunctions.

Inglewood, for instance, has a computer, but it does not monitor traffic at intersections, and some of the city’s intersections are not equipped with sensors, said Charng Chen, associate traffic engineer for Inglewood.

The city of Los Angeles has a system downtown similar to the one planned for Gardena, except that it monitors traffic by the second instead of the minute, Natsuhara said.

He said Gardena’s system, making less-frequent adjustments to signal lights that otherwise are set according to the time of day and daily traffic patterns, will be more efficient than attempting second-by-second adjustments.

“We’ve taken the best from all the systems we’ve looked at and combined them,” said Ayers, who visited Nashville, Tenn., and other cities to study the latest technology.

Gardena won the grant funds for the project from an annual pot of about $6 million that the federal government returns to Los Angeles County from federal gasoline-tax revenue, said David Yale of the county Transportation Commission. Another $25 million in gas-tax proceeds are distributed countywide strictly on the basis of population, Yale added.

Yale said the commission awards the grants to areas where traffic is congested and where improvements in local roads will relieve pressure on freeways.

Gardena’s heaviest traffic is on several east-west streets used by commuters going to and from the Harbor Freeway just east of the city, Natsuhara said.

Rosecrans Avenue, for instance, connects with the Harbor Freeway and carries a daily average of 45,500 cars through this city of 50,800 people, according to city reports. By comparison, Compton Boulevard, which runs parallel to Rosecrans but does not have a freeway interchange, is used by an average of 16,500 cars.

Commuters using the San Diego Freeway, which has two exits just south of the city, also pass through Gardena’s streets, Natsuhara said.

Even when the computer system is installed, problems could still arise at the city’s borders, officials warned. If cars are hurried through the city only to run into congestion where the system ends, Ayers pointed out, the project might lose some of its value.

In a larger city, controlling traffic at the borders might be only a minor concern, Tsiknas said, but in Gardena congestion at one end of the city could spread to the opposite end.

The system will try to cope with this by supplying the computer with information on traffic lights just outside the city, traffic consultant Tsiknas said. Although the computer will not be able to alter the timing of these lights, it will be able to synchronize Gardena’s signals with them, he said.

Cities with similar traffic computer systems have reported software glitches and communication problems between the field and the central computer, said Kwan Lau, an electrical engineer in Caltrans’ traffic operations division.

If the computer crashes, city officials said, signal lights will be set by controllers at the intersections, as is done now. Some Gardena intersections presently have traffic sensors, but they control only the lights at that intersection.

In the future, more and more cities will be turning to centralized computer systems, said Kwang Hu, a traffic engineer for the city of Los Angeles. Eventually, Hu said, linked computer-run systems will span the nation.