Ramp Metering to Expand : Traffic: Meters will be activated along the Riverside Freeway on-ramps from the Costa Mesa Freeway east to the county line.

There seems to be no escaping them. At almost every freeway on-ramp in Orange County, a meter stands guard. Like nightclub bouncers, the meters only let vehicles through when there is room available.

The reasoning behind meters is simple. Freeways carry fewer cars than they are capable of when traffic flow is disturbed and nothing disturbs traffic like a herd of cars trying to squeeze onto a crowded freeway at once. In contrast, a single car merging into traffic causes little disruption.

Some drivers believe in meters. Others believe that things would work just as well, or as badly, without them. Love them or hate them, about 80% of Orange County’s 300 on-ramps are metered, and more are on the way.

In October, meters will be activated along the Riverside Freeway, from the Costa Mesa Freeway east to the county line. Caltrans expects that $2-million project, which includes other ramp improvements, may win a few converts to metering if congestion is reduced as expected. Installing a meter on a ramp costs $25,000.

Every evening, commuters leaving the county encounter a bottleneck where the Riverside Freeway traverses Santa Ana Canyon. Non-metered ramps are blamed for part of traffic hassle. They offer no deterrent to commuters who use surface streets to bypass the freeway as far as possible.

When these commuters finally pile onto the freeway en masse, traffic is unable to cope. Some cars must slow down to make room while others change lanes. The freeway flow breaks down.

“That breakdown in the freeway reverberates all the way back, and that’s where we get our stop-and-go traffic,” said Glenn Murphy, a Caltrans traffic engineer.

The benefits of metering are fresh in Murphy’s mind. His Caltrans office in San Bernardino added meters in June along the Riverside Freeway, from the Interstate 15 to the Orange County border. That regulated the morning commuters who were flowing unchecked onto the freeway and causing tie-ups.

The effects have been dramatic. A preliminary survey shows that the average commute along the metered section during the worst of rush hour dropped from 35 to 22 minutes. It was so noticeable that commuters with mobile phones were raving about the change on a local radio station.

“A lot of folks are really happy,” said Jill Angel, a traffic reporter with KNX 1070 AM. The station takes calls from “Traffic Tipsters,” motorists who call to report traffic problems.

The trade-off to metering is that drivers must wait on a ramp, of course. That may seem an eternity to a frustrated commuter, but the time spent should be thought of as a deposit: It’ll be returned once on the freeway.

“All the data show that this time is more than recovered once they’re on the freeway,” said Joe El-Harake, a traffic analyst in the Orange County Caltrans office.

How long drivers have to wait on a ramp depends on a variety of factors, such as the level of congestion on the freeway and the size of the freeway ramp, El-Harake explained.

Timers turn meters on for morning and evening rush hours, most controlled by sensors embedded in the freeway that regulate how often cars can go through.

If there is no congestion, meters will show a steady green light. When traffic hits a certain level, metering begins. The heavier the traffic, the fewer cars released per minute onto the freeway.

At their slowest, meters on long ramps might only allow three to four cars per minute while meters on short ramps might allow five or six cars per minute. This is because long ramps have the room to “store” cars while short ramps easily fill up and spill traffic onto surface streets.

Sometimes, Caltrans may use a surface street lane to hold traffic, if the lane is dedicated for cars getting on the freeway. Generally, however, the goal is to avoid backups.

For example, traffic sensors at ramp entrances usually speed meters up if traffic is detected spilling onto surface streets. Also, on some short ramps, two cars may be allowed through per green. It’s a compromise, but it is far better than an unregulated flow, El-Harake said.

Many ramps have unmetered lanes for car pools. Because there are relatively few car pools, they pose little threat of disrupting the freeway by entering unregulated. If the situation changes, car-pool on-ramp lanes might also be metered, though the wait would probably be much shorter than in normal lanes, El-Harake said.

Among the common complaints that Caltrans often hears is that metering occurs even when traffic problems have disappeared. Generally, this is because Caltrans has forced a signal to keep metering in an effort to ease congestion known to occur farther down the freeway.

In the future, Caltrans hopes to have meters talk to each other. That way, if a freeway meter senses a lot of congestion, it can signal to other meters “upstream” to restrict traffic.

Also in the future are more meters--these along the northbound Orange Freeway in about six months and in a few years along Interstate 5 south of the El Toro Y. When these projects are finished, Orange County will be more or less meter complete.

Freeway Meters Control the Flow

Ramp meters regulate the entrance of cars onto a freeway. Timers activate the meters for morning and evening rush hours while sensors control how many cars they let through per minute.

The Sensor Loop: Sensors are loops of wire buried in the road. Electricity flowing through them creates a magnetic field. Metal in cars disturbs this field, causing detection.

1) Sensing Congestion: Sensors in freeway lanes measure traffic every 30 seconds. The heavier the congestion, the fewer cars per minute allowed past the ramp meter.

2) Anyone Waiting? During congested conditions, the meter stays on red until sensors detect waiting cars. Then the meter lets them through, one by one.

3) Speed It Up! A sensor near the ramp entrance detects when traffic is about to spill onto surface streets. When triggered, it usually forces the meter to accelerate.

Watching: When there is little traffic, signal stays on green. Meter is on but only watching for congestion. Brief yellow light warns of change from “watching” to “metering” mode.

Metering: Congestion triggers metering. Red light stops cars before they proceed.

Why Metering Helps

NOT METERED: Without metering, cars can enter the freeway in a large group. During rush hour, there is no room to absorb the group all at once. Traffic on the freeway must slow or change lanes to make room for the newcomers. Freeway flow is disrupted.

METERED: With metering, cars are sent onto the freeway alone or in pairs. It is easier for the freeway traffic to absorb a metered dose of vehicles than a large group of cars. Sensors help the meter know how many cars per minute the freeway can handle.

Source: Caltrans

Researched by DANNY SULLIVAN / Los Angeles Times