Wednesday, November 23, 2016

In the Golden State, a Golden Anniversary for Ramp Meters

Ramp metering in use on northbound Interstate 405 in the city of Los Angeles.

Many drivers are familiar with ramp meters, widely used in California to control the flow of vehicles entering freeways. But few may know 2016 is an important anniversary of this cost-effective tool for smoother traffic.

Exactly 50 years ago, ramp meters made their California debut. In 1966 the Golden State’s first experiment with them took place in Los Angeles County in Caltrans District 7.

The next half-century showed the value of ramp meters in fighting gridlock and increasing average traffic speed. Now, almost 3,000 ramp meters are in use throughout California, according to Caltrans figures as of December 2015. Ten of the 12 Caltrans districts statewide operate ramp meters or anticipate doing so by 2025.

But in 1966 they were an innovative idea, introduced only three years earlier in Chicago and then in the Detroit area.

District 7 saw ramp metering as a possible answer to a bottleneck on Interstate 5 (Golden State Freeway) at the northern edge of Los Angeles.

“It all began on the last day of the Memorial Day weekend at the junction of Routes 5 and 14, in the foothills in northern Los Angeles. Recreation traffic returning home from the holiday jammed the interchange between these two routes, resulting in ‘intolerable’ delay. It was decided that something would have to be done to prevent a repeat of this type of congestion,” Stuart Harvey, former deputy director of Caltrans District 11 in San Diego, wrote in a 1990 short history of ramp metering in the state.

So District 7, through its newly created Freeway Operations Department, crafted a plan it unveiled at the 5/14 junction on the 1966 Labor Day holiday.

“Traffic Operations staff decided to try regulating the flow onto Route 5 with a portable traffic signal under manual control,” Harvey wrote. “The actual control mechanism which was employed might be considered primitive by modern standards.” But it worked and was remarkably effective.

Ramp metering on northbound U.S. Highway 101 in Thousand Oaks.

Indeed, the experiment “was very successful in controlling congestion and delay, and it was decided to refine the technique,” Harvey added.

“On the next holiday, Christmas Monday, the same basic method was used, except that the portable traffic signal was programmed to cycle automatically and the cycle length was manually adjusted to account for changing conditions on the freeway.”

The tryout was judged a complete success, and District 7 made plans for another ramp meter audition in the heart of Hollywood.

Only months later, on April 11, 1967, California's first two permanent fixed-time ramp meters were activated on the northbound U.S. Highway 101 (Hollywood Freeway) at Sunset Boulevard, with corresponding northbound ramp closures at Hollywood Boulevard from 4 to 6 p.m.

Before throwing the switch, however, District 7 worked closely with the city of Los Angeles to prepare the public for the historic step.

“There was a grave concern on the part of the community, particularly the Hollywood Chamber of Commerce, about the impacts of ramp metering,” William E. Schaefer, former deputy director of project development and chief engineer of Caltrans, said in an oral history interview recorded shortly before his retirement in 1990. Schaefer was design engineer in District 7 during the introduction of ramp metering.

“It was pretty carefully planned out. We spent a number of meetings with the Hollywood Chamber of Commerce convincing them that it was worth giving it a try,” Schaefer said.

“That first night, I was comfortable it would work,” Schaefer recalled. “I took some of the officers of the chamber with me in my car to go around through the project to show them that it worked. And it worked beautifully.”

The project successfully relieved congestion on the freeway mainline without seriously affecting surface street operations. Freeway delay was reduced by about 75 percent.

“In that early primitive stage,” Schaefer said, “we operated the metering with a little button with a guy behind the bushes. So we didn’t have any sophisticated equipment. We simply had a traffic light with some power and a button to change the signals. And then we put in a normal, little old fixed-time controller. It was a very, very primitive system but it really worked great. And from that we moved on to a lot of other projects.”

Today, most ramp meters in California respond automatically to freeway traffic conditions monitored by inductive loop detectors in the roadway. When the freeway flows freely, more cars are allowed to enter.

Systems also can use centralized monitoring of traffic conditions to help determine the metering rates for all of the ramp meters along a corridor.

The objective, just as 50 years ago, is to limit freeway congestion. Studies show the success of ramp meters in promoting more efficient overall operation of freeways with higher average speeds and fewer collisions and delays.

California’s highway system has about 2,954 meters as of December 2015. District 7 has about 1,024 metering locations, including 28 freeway-to-freeway connector meters, making it the largest ramp metering district in the state and nation.