The phrase "one car per green" turned 50 last week. Don't all get up to celebrate at once.
California got its very first ramp meter April 11, 1967 on Sunset Boulevard at the 101 Freeway. Their purpose was simple: To help decrease bottlenecking and to cut down on pollution.
But even though on-ramp lights have been around longer than most of today's motorists have been driving, they continue to frustrate and confuse even the fiercest of road warriors.
Experts, however, contend they're an effective way to keep traffic flowing smoothly.
One such expert is Wahib Jreij, acting senior transportation engineer for Caltrans. He joined Take Two to talk about it.
When ramp meters were originally put in place, what was the theory behind them?
The purpose of ramp meters is to help the freeway mainline traffic.
It's easy to understand when you think of water: If you have a river that's flowing very smoothly and you have a lot of streams coming into the river, you can see where another input comes in there will be trouble in some of the water. When water comes from the side, it creates a wave and turbulence in the stream. It's the same with traffic.
If you stop this flow of cars, you're going to ease immersion and help alleviate that bottleneck or turbulence.
Looking at the big picture: How have ramp meters affected traffic flow in California since that day in 1967?
After 1967, we noticed it was a great success, and since then we decided that we were going to install ramp meters on all L.A. freeways because that's the way to make traffic flow better.
But we learned that ramp meters do stop vehicles, but they also have to be traffic responsive, meaning that they have to work only when they're needed to work. We don't want to stop cars when there's no need to stop cars.
To do that, we had to install loops on the freeway. So every on-ramp that comes into the freeway had detectors on the mainline freeway adjacent to the light. Those detectors detect the vehicle's volume and occupancy on the mainline.
If you have a freeway that's moving at 70 miles an hour or better, a lot of times your light will be green. When the freeway's congested with speeds falling below 50 to 40 miles an hour, you need to stop and wait for a cycle to go green. So now all our ramp meters on the L.A. freeway system are called "local traffic responsive."
What would happen if Caltrans decided to dump the ramp meter thing tomorrow?
I think for sure we would have a lot more congestion. I have no doubt on that.
There was a study done in Minnesota in the 2000s. The Twin Cities in Minnesota installed ramp meters and people were so upset. Jesse Ventura was the governor of Minnesota, and he said 'OK. We're going to turn these ramp meters off for six weeks, and we're going to do an evaluation study to see if they work.' And that's what they did.
They turned off all ramp meters in the Twin Cities — about 400 of them — and they found out that without ramp meters, the level of congestion was higher, accidents were dramatically higher, and travel-ability was off.
Without ramp meters, it was hard to predict how long it would take to get to work. Some days it took an hour, sometimes it took an hour and a half. It always took longer, but it sometimes took way longer, sometimes just a bit longer. Accidents rose by quite a bit, especially sideswipe accidents. People were just merging without looking. Also, congestion was way up.
When you improve freeway speed, even by one or two miles an hour, you move a lot of vehicles through one point. Even if you might not notice, it makes a big difference for the overall traffic flow.
Press the blue play button above to hear the full interview.
(Answers have been edited for clarity and brevity.)