Ramp Meters

ADOT expands network of adaptive Valley freeway ramp meters

ADOT expands network of adaptive Valley freeway ramp meters

I-17 101 traffic interchange

ADOT expands network of adaptive Valley freeway ramp meters

ADOT expands network of adaptive Valley freeway ramp meters

October 2, 2023

Updated technology improves how ramp meters operate

PHOENIX – The Arizona Department of Transportation continues to upgrade the Phoenix area’s network of adaptive freeway ramp meters used to improve the flow of traffic, especially during busy rush hours.

The improvements have not required the installation of new ramp meters. ADOT has instead used enhanced computer programming to operate the timing of the meters’ alternating green and red traffic lights to provide valuable space between vehicles entering a freeway.

Ramp meter upgrades were completed this year along the 60 miles of Loop 101 in the Phoenix area – from near I-10 in the West Valley all the way around to Loop 202 (Santan Freeway) in Chandler.

Adaptive ramp metering was first tested with positive results in 2019 along State Route 51 in Phoenix, followed by stretches of I-10 and I-17. Approximately 75 percent of the more than 250 ramp meters along Valley freeways now operate using the upgraded system. 

The improvements mean each ramp meter can now respond to traffic conditions farther away from any one specific freeway location.

For example, an adaptive ramp meter is able to respond to slowing or improved traffic conditions beyond its immediate on-ramp location. Data about conditions a mile ahead along the freeway allows the meter to adjust the timing of its green and red lights. This process can be repeated along several miles of a freeway until traffic conditions improve.

Ramp meters help balance the overall amount of traffic along a freeway to enhance traffic flow. From a safety standpoint, the room between vehicles entering a freeway can enhance merging conditions and reduce the risk of crashes.    

 Adaptive ramp meters also have been set at times to operate outside of traditional weekday rush hours to help manage traffic flow when nearby sporting events, concerts and even weekend construction closures are taking place.  

ADOT will continue to expand the use of adaptive ramp metering to additional sections of freeway in stages over time.

Ramp meters along a Phoenix-area freeway (ADOT file photo Sept 2023)

I-17 ramp-meter lights have role in wrong-way vehicle system

I-17 ramp-meter lights have role in wrong-way vehicle system

I-17 101 traffic interchange

I-17 ramp-meter lights have role in wrong-way vehicle system

I-17 ramp-meter lights have role in wrong-way vehicle system

August 1, 2018

PHOENIX – Phoenix-area drivers are used to seeing freeway entrance-ramp meters with alternating green and red traffic lights during weekday rush hours. But some of the red lights in Interstate 17 ramp meters also play a role as part of the pilot wrong-way vehicle detection system being tested by the Arizona Department of Transportation.

When a wrong-way vehicle is detected by the thermal camera-based technology now in place along 15 miles of I-17 in Phoenix, the system also turns on the red lights in nearby entrance ramp meters to try to hold “right-way” traffic from entering the freeway.

“While most drivers aren’t used to seeing a solid red light displayed by a ramp meter for more than a few seconds, we want I-17 drivers in Phoenix to know there is a reason for that to happen – a wrong-way vehicle may be ahead on the freeway,” said Susan Anderson, ADOT’s systems technology group manager.

Via the I-17 pilot project’s decision support system, the red lights on entrance ramp meters are programmed to turn on within 3 miles of a detected wrong-way vehicle. If the vehicle continues along the freeway, additional ramp meter red lights will be activated. The red lights are programmed to return to their normal mode for that particular time of day or night, including turning off, after the system detects that the wrong-way vehicle is no longer in the area.

“As we test the overall wrong-way vehicle alert system and research its performance over the next several months, it’s important to note that the ramp meter red lights are one of several countermeasures,” Anderson said. “The ramp meter lights are traffic signals, so I-17 drivers on entrance ramps should be prepared to stop if the light is a solid red, no matter what time of day.”

The first-in-the-nation I-17 system features 90 thermal detection cameras positioned above exit ramps as well as the mainline of the freeway between the I-10 “Stack” interchange near downtown and the Loop 101 interchange in north Phoenix. When a wrong-way vehicle is detected entering an off-ramp, the system is designed to trigger a background-illuminated “wrong-way” sign to try to get the driver’s attention.

Alerts also are immediately sent to ADOT’s Traffic Operations Center and the Arizona Department of Public Safety so traffic operators can quickly activate freeway message boards to warn other drivers while state troopers can respond faster than relying on 911 calls.

Since it went operational in January, the system has detected more than 30 wrong-way vehicles entering I-17 off-ramps and frontage roads. One vehicle was detected on I-17 in north Phoenix on July 5 and the driver was stopped by AZDPS. The majority of drivers in vehicles detected by the I-17 system have turned around on exit ramps without entering the freeway.

Next round of SR 51 ramp meter adjustments begins

Next round of SR 51 ramp meter adjustments begins

I-17 101 traffic interchange

Next round of SR 51 ramp meter adjustments begins

Next round of SR 51 ramp meter adjustments begins

August 7, 2017

PHOENIX – Starting this week, the timing of ramp-meter signals along southbound State Route 51 (Piestewa Freeway) are being adjusted to respond to the flow of morning rush-hour traffic, expanding an Arizona Department of Transportation program that began last fall along the freeway’s northbound on-ramps.

Instead of the ramp meters being programmed with predetermined red-light intervals, the system will use data from traffic-flow sensors embedded in the freeway’s pavement to adjust the signal timing. When morning rush-hour traffic slows, the ramp meters may hold vehicles several additional seconds to help ease the congestion.

The change involves southbound SR 51 on-ramp meters from Greenway to Thomas roads. The southbound ramp meter at Shea Boulevard isn’t currently in use.

As with the northbound State Route 51 ramp meters during the afternoon rush hour, the southbound meters may even turn off earlier in the morning based on how well freeway traffic is flowing.

Drivers may notice new signs along southbound SR 51 on-ramps advising them of the signal timing changes.

The ramp meter project supports one of ADOT’s key performance indicators under the Arizona Management System championed by Governor Doug Ducey: reducing the percentage of time freeways in the Phoenix metro area are congested.

Ramp meters have been in use for many years across the country and at many Phoenix-area freeway on-ramps during busy rush hours to enhance traffic flow, as well as safety, by controlling the number of vehicles entering freeways at any one time.

The upgrades along SR 51 provide a way to look at expanded capabilities of ramp-meter technology. Most ramp meters along Valley freeways are currently programmed with predetermined red-light intervals. Hours of operation for the meters have been based on historical traffic data.

The SR 51 ramp meters using the new responsive system are programmed to adjust to freeway traffic flow and the volume of traffic entering the freeway. Detectors along the entrance ramps also assess if ramp traffic is backing up, allowing the system to further adjust the red and green light timing to limit the amount of traffic waiting to enter the freeway.

ADOT is working closely with the city of Phoenix on the ramp meter research project and will continue to monitor any impacts to traffic on local streets intersecting with SR 51.

Completed Loop 101 widening means reduced use of ramp meters

Completed Loop 101 widening means reduced use of ramp meters

I-17 101 traffic interchange

Completed Loop 101 widening means reduced use of ramp meters

Completed Loop 101 widening means reduced use of ramp meters

December 8, 2016

PHOENIX – One of the benefits of the recent widening of Loop 101 in the Scottsdale area is that on-ramp meters, featuring those alternating green and red traffic signals, won’t be in use as often now.

The Arizona Department of Transportation followed up on the addition of new Loop 101 lanes by assessing improved traffic conditions between Frank Lloyd Wright Boulevard and Loop 202 (Red Mountain Freeway). The result: Most ramp meters in that area will now be used about half as often as they were before ADOT launched the $73 million project to improve 11 miles of Loop 101 south of Shea Boulevard.

The ramp meters in the Scottsdale area weren’t in use during construction, which included rebuilding on- and off-ramps along the freeway. Crews are scheduled to activate the meters again starting Monday, Dec. 12. Prior to the widening project, the meters were used during both the morning and afternoon peak commute times.

With reduced congestion, drivers can expect most Loop 101 ramp meters in the Scottsdale area to be used during only one peak commute period each weekday. 

For example, ramp meters along the busier northbound Loop 101 between McKellips and Indian Bend roads will only be in use from 7 a.m. to 9 a.m. weekdays. Conversely, most ramp meters along southbound Loop 101 between Frank Lloyd Wright Boulevard and McKellips Road will only be used during the 3 p.m. to 7 p.m. peak commute times. The hours of operation will vary slightly depending on location and anticipated traffic conditions (see the list below).

The northbound Loop 101 ramp meters at Via De Ventura, 90th Street and Shea Boulevard will still be used during both the morning and afternoon rush hours. At this time, the southbound Loop 101 ramp meter at Shea Boulevard and northbound meter at Cactus Road won’t be used at all. The southbound ramp meter at Raintree Drive will be limited to use during the morning rush hour.

Ramp meters are used to enhance traffic flow by providing space between vehicles entering freeways across the Phoenix area. That space between vehicles also promotes safer merging conditions for drivers who are either entering or exiting freeways.

Ramp meter use and hours of operation are subject to change depending on future traffic conditions.
 

---

 

Loop 101 entrance ramp meter schedule as of Dec. 12, 2016  

7 a.m. – 9 a.m.

Loop 101 North ramp meters at McKellips Road, McDowell Road, Thomas Road, Indian School Road, Chaparral Road, McDonald Drive and Indian Bend Road.

6 a.m. – 9 a.m.

Loop 101 South ramp meter at Raintree Drive.

3 p.m. – 7 p.m.

Loop 101 South ramp meters at Chaparral Road, Indian School Road, Thomas Road, McDowell Road and McKellips Road.

3 p.m. – 6:30 p.m.

Loop 101 South ramp meters at Frank Lloyd Wright Boulevard, Cactus Road, Indian Bend Road and McDonald Drive.

3:30 p.m. – 6:30 p.m.

  • Loop 101 South at 90th Street, Via De Ventura.
  • Loop 101 North at Raintree Drive and Frank Lloyd Wright Boulevard.

7 a.m. – 9 a.m. and 3:30 p.m. – 6:30 p.m.

Loop 101 North ramp meters at Via De Ventura, 90th Street and Shea Boulevard.

Note: Loop 101 North ramp meter at 90th Street will start at 3 p.m.

Not in use at this time

Loop 101 South ramp meter at Shea Boulevard and Loop 101 North ramp meter at Cactus Road.

 

ADOT tests how ramp meter timing can improve SR 51 traffic

ADOT tests how ramp meter timing can improve SR 51 traffic

I-17 101 traffic interchange

ADOT tests how ramp meter timing can improve SR 51 traffic

ADOT tests how ramp meter timing can improve SR 51 traffic

September 28, 2016

PHOENIX – With a goal of improving the rush-hour traffic flow, the Arizona Department of Transportation will test changes in the timing of ramp-meter signals along one Phoenix-area freeway.

Starting the week of Oct. 3, afternoon rush-hour drivers using on-ramps along northbound State Route 51 (Piestewa Freeway) are likely to notice longer red lights at ramp meters as ADOT takes a look at how the signal adjustments affect freeway traffic.

It will likely take a couple of days for the adjustments to be made at all of the northbound SR 51 ramp meters. The changes are expected to be in place for at least three weeks as part of this initial phase of tests.

As part of the testing, some northbound State Route 51 ramp meters may turn off at an earlier time during the afternoon rush hour based on how well freeway traffic is flowing.

The ramp meter project supports one of ADOT’s key performance indicators under Governor Doug Ducey’s call for continuous improvement among state agencies: decreasing the percentage of time freeways in the Phoenix metro area are congested.

Ramp meters have been used for years at many Phoenix-area on-ramps to enhance traffic flow as well as safety by creating gaps between vehicles entering freeways.

The testing along State Route 51 provides a way to look at the full capabilities of current ramp-meter technology. Adjusted ramp meters will respond to freeway traffic flow as well as the volume of traffic entering the freeway.

Ramp meters are currently programmed with predetermined red-light intervals. Hours of operation are based on historical traffic data.

As part of ADOT’s project, the red lights at the northbound State Route 51 ramp meters may hold vehicles for several more seconds, but detectors along the entrance ramps also will assess if ramp traffic is backing up. The system also is designed to adjust the red and green light timing to limit the amount of traffic waiting to enter the northbound freeway.

Heaviest rush-hour traffic conditions along northbound State Route 51 occur during weekday afternoons. ADOT’s project team has already been gathering data over the last several weeks for current ramp-meter and freeway conditions along the northbound freeway.

The ramp-meter timing changes may be kept in place beyond the three-week test period, based on results.

ADOT also will study another system of ramp-meter programming along southbound SR 51 in the near future, although the dates for that research haven’t been set. That additional programming system is designed to allow individual ramp meters to respond to traffic conditions even several miles away and adjust signal timing to help improve traffic flow along a longer stretch of freeway.

ADOT is working closely with the city of Phoenix on the ramp meter research project and will monitor any impacts to traffic on local streets intersecting with SR 51.

Ramp Meters: Unappreciated or just misunderstood?

Ramp Meters: Unappreciated or just misunderstood?

SR24-1

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.

Research Center guides ADOT toward transportation innovation

Research Center guides ADOT toward transportation innovation

SR24-1

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

SR24-1

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!