Intelligent Transportation System

Ramp Meters: Unappreciated or just misunderstood?

Ramp Meters: Unappreciated or just misunderstood?


Ramp Meters: Unappreciated or just misunderstood?

Ramp Meters: Unappreciated or just misunderstood?

February 5, 2014

A look at a Phoenix-area ramp meter in action.

There’s no delicate way to put this, so we’re just going to come right out and say it – we feel that ramp meters are underappreciated.

These signals control the flow of traffic entering a freeway, thereby helping to ease congestion. By managing queues of vehicles, ramp meters provide for safer merging of vehicles and mitigate potential collisions.

Yet, it’s not uncommon to see drivers totally ignore a ramp meter and drive right through its red light.

Maybe ramp meters are just misunderstood…

If that’s the case, hopefully this post will clear things up and give commuters a new respect for these signals. Today, we’re sharing with you a series of frequently asked questions (and answers) all about ramp meters.

Q) When traffic is light, couldn’t you just keep the lights green? It seems silly to have to stop when I’m the only car.

A) Having a continuous green light, even when there is no traffic on the ramp, could create a potential safety issue. For example, if a group of three or four motorists see a green light on the ramp meter, they will assume they do not need to stop. But, as soon as the first car reaches the detection, the meter will kick into action and a red light will show. Now the cars are traveling at speed and once one car attempts to stop for the red light, it could set up the possibility for a crash. That’s why our ramp meters “rest in red,” and not in green.

Is there any evidence to indicate these meters have actually improved freeway safety?

There are many studies available online to support the benefit of ramp meters. Basically, ramp meters help to increase freeway speeds, decrease travel times and reduce delays. Ramp meters have also been shown to increase freeway capacity and reduce crashes (specifically rear-end collisions). This explanation is given in the U.S. Department of Transportation’s Federal Highway Administration Ramp Management and Control Handbook: “The manner in which safety is improved depends on the type of ramp management strategy selected. Ramp metering improves safety by breaking up platoons of vehicles entering the freeway, thereby allowing more orderly and safe interactions between merging vehicles and freeway mainline vehicles.”

What should I do when I pull toward the ramp meter and the light turns green before I have a chance to stop? Am I allowed to proceed without stopping?

Ramp meters should be followed like any other traffic signal. If you reach the light when it turns green, you can proceed without stopping if it is safe to do so. But always be prepared to stop when ramp meters are active and remember that only one car can go per green light.

Some of these new ramp meters have what appear to be cameras above them. Are they photo radar cameras?

ADOT doesn’t have cameras at our ADOT ramp meter locations. What you may be seeing is the receiver for wireless detection.

Why can’t I just ignore the ramp meter’s red light? I see other motorists do it regularly.

It is illegal to run a red light on a ramp meter, just as it is against the law to run any red light. Ramp meters are to be followed just like any other traffic signal. Drivers who fail to obey the ramp meter signal can be cited (the violation falls under Arizona State Statutes 28-645 and 28-644). Ticket fines vary from county to county, but can typically range $140-180 and include points against your driving record.

ADOT library is focused on transportation research

ADOT library is focused on transportation research


ADOT library is focused on transportation research

ADOT library is focused on transportation research

October 25, 2011

Librarian Dale Steele oversees the collection at the ADOT Research Center Library. The library recently moved into a space previously occupied by the Roadrunner Cafe, a cafeteria for ADOT employees. The cafe moved out, but the sign stayed behind!

The ADOT Research Center Library might not carry any best-sellers, but where else are you going to find a title like, “Benefits of high volume fly ash: new concrete mixtures provide financial, environmental and performance gains”?

That study, published by the Federal Highway Administration in 2010, is on the shelves alongside thousands of publications – all of them focused on transportation planning and engineering.

Established in 1989 as part of the ADOT Research Center, the library is open to ADOT employees, transportation faculty in Arizona universities and others with an interest in transportation.

The goal is to keep a collection that not only preserves the information ADOT produces, but also includes reports from other state DOTs, transportation boards, federal transportation agencies and professional societies.

Librarian Dale Steele says having all this research and information on hand is valuable to ADOT employees who work each day on the state’s transportation system … it gives them recent data and a look at what other transportation departments are doing.

“Managing information is important to providing Arizona with a more efficient transportation system,” Steele says. “The library is a key part of getting current information to decision-makers.”

Steele searches online databases for the material and secures copies for the ADOT Research Center Library. He’ll often secure copies of ADOT reports for the state library and Arizona State University’s library.

Most states are starting to produce more of their information electronically, which means Steele doesn’t get a physical copy of the work. However, he does assist ADOT employees with literature searches and can access several online works.

“What we can do is find out what is out there and try to get it,” he said.

The ADOT library collection consists of nearly 30,000 books, magazines, videos and CDs! Here are a few more examples of titles lining the shelves …

* “Effects of yellow rectangular rapid-flashing beacons on yielding at multilane uncontrolled crosswalks,” Federal Highway Administration, 2010

* “Clarkdale transportation study,” ADOT, 2011

* “Roundabouts: an informational guide; second edition,” National Cooperative Highway Research Program, 2010

Research Center guides ADOT toward transportation innovation

Research Center guides ADOT toward transportation innovation


Research Center guides ADOT toward transportation innovation

Research Center guides ADOT toward transportation innovation

August 8, 2011

The ADOT Research Center studies ways to improve transportation in Arizona.

Much has changed since ADOT got its start in 1927.

Back then, the agency was known as the Arizona State Highway Department and roads certainly were built a little differently. Methods, materials and technology have changed so much since then.

Amazingly, they’re still evolving today …

ADOT keeps up with transportation advancements through research. The ADOT Research Center oversees that research, which is aimed at improving all aspects of transportation in the state and beyond.

But, don’t think the studies and research produced by this team just sit on a shelf once completed.

The information generated by ADOT’s Research Center focuses on evaluating new materials and methods. ADOT’s researchers look at developing design and analysis techniques and study the underlying causes of transportation problems.

In other words, this research leads to better methods, innovative practices and new ways of doing things, giving Arizonans a better value when it comes to transportation!

To get an idea of how this research ends up influencing the way ADOT operates, take a look at the seven emphasis areas within the ADOT Research Center :

  • The Environment emphasis explores the interaction between transportation and the environment. Studies from this discipline look at air quality policy, emissions reduction, transportation-generated noise, wildlife and other environmental topics.
  • The Maintenance emphasis researches how to enhance the maintenance and operation of roadways. A recent study is evaluating the effects of snowplow and deicing chemicals on rubberized asphalt pavements.
  • Materials and Construction studies scrutinize the products and methods used in constructing roads. One study from this emphasis provided research into the noise reduction properties of rubberized asphalt.
  • Research within the Structures emphasis area aims to apply effective modern technology and resources to enhance the implementation of bridge management systems, including the repair of over-stressed bridge decks.
  • Traffic and Safety research not only investigates engineering principles to help solve traffic problems, but it often takes into account the psychology and habits of drivers. Research projects have included a study on seat belt usage in Arizona.
  • Intelligent Transportation Systems analyzes ways to integrate advanced communication technologies into transportation infrastructure. Study topics have included freeway ramp metering, electronic message signs and emerging technology.
  • The Planning and Administration discipline looks to our transportation future – how ADOT can best meet travelers’ needs as the population grows, our society evolves and technology offers more options. This emphasis also addresses organizational issues within ADOT. One ongoing study within this emphasis will report on how new media can bolster ADOT’s community outreach.

There’s much more to learn about this team. Visit the Research Center’s webpage for additional information and stay tuned. In the future we’ll blog about the ADOT Research Center ’s library and product evaluation program.

Getting the green light: Valley ramp meters now more efficient

Getting the green light: Valley ramp meters now more efficient


Getting the green light: Valley ramp meters now more efficient

Getting the green light: Valley ramp meters now more efficient

June 23, 2011

If you drive Valley freeways during rush hour, you’re probably pretty familiar with ramp meters …

They’re the two-light signals positioned at most Valley on-ramps that tell motorists when it’s okay to head onto the freeway.

Ramp meters have been used in the Phoenix-Metro area for about the past 20 years and maybe you think not much about them has changed … but, actually they’ve recently become much more efficient!

Thanks to a project funded through the Maricopa Association of Governments (MAG), roughly 300 ramp meters have been replaced with units that use newer, smarter technology.

As ADOT’s Intelligent Transportation System Supervisor Chuck McClatchey explains in the video above, the older ramp meters were not nearly as efficient as the new models.

“The new controllers actually operate totally independent of each other, which, means you can have 15 cars in one lane, no cars in the other lane and it will give 15 straight greens and just maintain red on the left side,” he said. “The older technology would give two greens and then a green to the non-existent cars. … So you can see that it really was not that efficient.”

But how does the ramp meter “know” a car is ready and waiting to take off onto the freeway?

Well, there are actually sensors in the ground adjacent to the signals that can detect a car as it pulls up. The ramp meter will then give a green light and start metering back and forth between the two lanes.

The meters also get information from the mainline, or freeway.

If the mainline is free-flowing, then the ramp meter will put on as many cars as possible. But if the mainline traffic slows down, the sensors pick that up and the rate at which cars are given a green light slows down some to help relieve the congestion.

The system has something called a queue-loop located at the very top of the ramp, too. The queue-loop is kind of a manual override that senses when traffic is backed up on the ramp completely up to the top. If that happens, the loop is activated and the metering goes to the fastest rate until the ramp is cleared. Basically, it’s a safety factor that keeps traffic from backing up into the surface street intersections.

All these features add up and help make it a little easier for motorists to get where they need to go!