Rhythm Engineering Blog

What Makes In|Sync Different?

We’ve been working vigorously at developing an advanced adaptive traffic control system since the beginning of Rhythm Engineering. When developing In|Sync in 2005, Rhythm Engineering used creative approaches and technologies new to the transportation engineering industry. Instead of developing incremental improvements to existing traffic control tools and methods, we imagined the best possible traffic control tool and went from there.

Our exploration led us to the human brain, or rather, the brain of a well-informed traffic engineer. Once we understood that no existing machine or method matches the analytical, reasoning and observational abilities of a traffic engineer, we set out to build one. We challenged ourselves by asking, “How would a traffic engineer control a signal if he/she were standing at each intersection?” We then built a solution that comes as close as possible to emulating that decision process and its benefits.

Emulating a well-informed traffic engineer at each intersection means In|Sync must detect demand in real-time, be able to make immediate adjustments in signalization, not be constrained by “mechanical” thinking and be aware of upstream and downstream traffic conditions. In other words, In|Sync at each signal must know the actual traffic conditions, have the power to make dynamic changes and appreciate what conditions will exist in the next few minutes.

This is a substantial departure from other traffic management systems. Nearly all traffic control systems today use digital hardware but remain constrained by analog thinking such as common cycle lengths, set sequences, fixed offsets and standardized allotment of green time, or splits. The In|Sync Processor is instead a modern state machine, meaning it can dynamically choose which phases to serve and instantly adjust and coordinate service and green time.

By adapting to actual traffic demand, In|Sync truly is superior to predetermined signal timing plans that, at best, estimate traffic demand based on a small historical sampling and generalize those results across years of traffic signalization. In|Sync’s ability to constantly see and flexibly serve actual demand in the best way possible is what enables it to produce such astounding before-and-after results. Regardless of your traffic flow, time of day or demand, In|Sync responds specifically to your intersection’s needs.

View In|Sync case studies and learn more about the advancements adaptive traffic control brings to intersections and communities by visiting our Case Studies page.

Rhythm EngineeringWhat Makes In|Sync Different?

What is Adaptive Traffic Control?

Adaptive traffic control systems help improve communities and intersections across the world. But what is an adaptive traffic control system? Today we hope to clear that up.

Adaptive traffic control systems aren’t as complex as they sound. At the very base, its technology that makes traffic signals change and adapt based on actual traffic demand. So rather than adhering to a fixed cycle — like the majority of traffic controllers and systems used — an adaptive system responds, in real-time, to the vehicles at the intersection.

This is done with a combination of advanced hardware and software. You need measuring systems to recognize the demand of traffic, that’s the hardware. At a rudimentary level this could be loops, but it could also be a camera or thermal camera. What these detection sources do is recognize vehicle presence and feed that information into the software.

For software, you need an advanced system and algorithm that can recognize vehicle counts and stays, analyze incoming data and push out responses regardless of intersection geometries or traffic demand. The software is what makes the traffic controller adaptive by responding to vehicle presence at any given time and appropriately prioritizing signal changes.

Advanced algorithms can be designed to respond with real-time optimization and coordinate traffic movements across corridors — meaning signals can be linked across a section of roadway, rather than at individual intersections. When signals are adaptive at a corridor-level, larger groupings of vehicles can be moved smoothly along stretches of road in a way that improves overall traffic flow.

For accuracy, adaptive traffic control algorithms are rigorously developed and tested to ensure accurate, responsive and advanced adaptive operations take place. At times, traffic is predictable, but that isn’t always the case. That’s why adaptive systems have to be prepared for anything.

That’s what an adaptive traffic control system is — a 21st century solution for optimizing traffic signals. Adaptive traffic controls respond directly to demand at every intersection, 24/7/365. And that’s what makes this solution different. Regardless of your traffic flow, time of day or demand, adaptive traffic control responds specifically to your intersection’s needs.


Learn more about Rhythm Engineering’s adaptive traffic control In|Sync.


*According to the Virginia Center for Transportation Innovation & Research, “Evaluation of the Virginia Department of Transportation Adaptive Signal Control Technology Pilot Project.”

Rhythm EngineeringWhat is Adaptive Traffic Control?

Traffic Signals: The Troubling Truth

As a typical motorist who hates sitting at long red lights, it is reassuring to know that there is so much that occurs behind the scenes to control traffic congestion.  As we learned in the first blog (7 Traffic Myths Debunked), there are a number of reasons we get into a jam!

Here’s a ‘crash course’ in traffic engineering which will illuminate the real reasons traffic signals seldom function as we want them to.

Essentially, traffic signals can be considered to have 3 major parts: 1.) Traffic signal heads, 2.) Vehicle sensors or detectors, and 3.) Traffic signal controllers and cabinets.  As with a police officer directing traffic in a busy intersection, these parts must work together to make the best decisions for optimal traffic flow. Thinking of the officer analogy, this makes sense: his brain would be the signal controller; his eyes the sensor; and his hands the signal head. He must effectively observe, make decisions regarding signals, and communicate them to motorists to ensure their safe and efficient travel; this is the same way traffic signals work.

1. Traffic Signal Heads

As pedestrians and motorists, we’re all extremely aware of signal heads; they are generally mounted on mast-arms or hung on wires spanning the intersection (aptly called “span wires”) and have three color-coded indications. As many of us have known since playing rousing games of “Red Light Green Light” as youngsters, these lights let us know when to stop and go, respectively. The middle, amber—or more commonly “yellow”—light alerts us to prepare to stop.

Most of us only think of this traffic signal component when expressing our frustration with red lights. When we must abruptly stop at yet another intersection, we’re more likely to shake our fists at that stubborn red light than any other part of the traffic signal system. In addition, these are often the most updated component of the three-part system.  In fact, most signal heads now use Light Emitting Diode (LED) lights in order to conserve energy. While signal heads may have the greatest presence in the public view of traffic signals, they are not as critical in signal optimization as the other two components.

(image source)

2. Vehicle Sensors

The next most infamous component is the subject of many of the myths described in the first blog: the vehicle sensor. The vehicle sensor detects the presence of vehicles at the stop bar of each lane, though it is neither a laser curtain nor a buried scale. The information collected by the sensor is binary, reading either “yes, at least one vehicle is present” or “no, not even one vehicle is present.”

Depending on the technology utilized, a sensor may or may not recognize the presence of more than one car. Once collected, this information is sent to the traffic signal controller for processing. The sensor is usually an inductive loop located beneath the pavement, though newer video technologies are growing in popularity. Two other less popular methods of detection include radar-based detection and detection using wireless magnetometers. Regardless of its form, the role of the vehicle sensor is always to detect cars and communicate that information to the signal controller.

…role of the vehicle sensor is always to detect cars and communicate that information to the signal controller.

Most intersections currently employ inductive loop sensors. Electromagnetic induction-based detectors use coils of wire under each lane. These coils are commonly referred to as “inductive loop detectors” or “loops.” This method works based on the laws of electromagnetic induction; when a mass of metal is moved inside a coil of wire, electricity or an electric pulse is generated. With these sensors, the vehicle is the mass of metal that moves inside the coil of wire buried under the lane. The detector constantly monitors the electric pulse in the loop and informs the traffic signal controller about the presence or absence of a car. Since induction-based detection relies directly on the laws of physics, if configured properly, it offers the most reliability.

While inductive loop sensors provide reliable feedback, installation and maintenance are costly and time consuming. To install loops, the pavement on each lane is cut with a saw in the shape of the loop. Loop wires are then installed into the saw cut and sealed. Over time, pavement moves and as a result, loop wires are broken. Regular pavement maintenance projects also destroy loops, necessitating premature reinstallation.

Furthermore, this methodology is limited: it does not know whether there is one vehicle or a string of vehicles waiting. Loop sensors can only detect the presence of cars idling at the stop bar. As a consequence, loop sensors do not allow for more complex traffic mitigation, which could give preference to busier streets in order to relieve traffic congestion. If you have seen a solitary car on the side street given priority (and green indication) over a long line of cars approaching on the main street, this limitation is likely the reason.

Another detection method is based on video image processing. This method has gained popularity because its installation is less intrusive and its maintenance is easier. In video based detection, cameras are mounted on mast arms from which vantage point they record approaching traffic. 

These (video) sensors are the little white, tubular objects sticking up from the signal mast-arm and staring at you. Fear not, these sensors aren’t recording your speed or your steering wheel drum solo!

The cameras send real-time images to an image processor. When pixels in the image don’t change over time, the processor saves them as a “learned” background image. The processor compares the real-time image with the learned image by literally subtracting the real-time image from the learned background image. If objects are left over from this subtraction process, the processor reports that a new car is present in its detection zone.

Installing cameras on mast arms is the only invasive step for deploying video image processing detection. If a camera fails, unlike replacing the loop, where the pavement has to be saw cut again, it is relatively easy to replace the failed part. However, video detection is susceptible to camera issues such as being blinded by the sun, fog, and snow. Additionally, shadows of moving objects and reflected light from wet pavements can generate false detection triggers. These false detection triggers bring up green lights even when there are no cars waiting to be served. Fortunately, software exists to readily compensate for these issues, thereby eliminating these issues and optimizing video detection sensors.

3. Traffic Signal Controller/Cabinet

If you’ve ever wondered about the purpose of the metal box at the corner of every major intersection, aside from being a public bulletin board or convenient place to unload an unwanted wad of gum, it is actually the traffic signal cabinet. The cabinet houses the signal controller and other hardware required to run the traffic signal. Based on input from the sensors set up at every intersection and the programming done by a traffic engineer, the signal controller determines the amount of green or “go” time given to each movement of cars. As such, it functions as the brains of the operation—aside from the traffic engineer, of course.

While they may look similar from the outside (i.e., big, metal boxes, possibly covered with graffiti), not all traffic signal controllers run in the same fashion. In fact, there are three modes of signal operations in the popular analog traffic signal controller. Most traffic signals operate using one of the following modes: pre-timed, actuated or synchronized.

The simplest of the three modes is the pre-timed mode. In the pre-timed mode, each vehicle movement is given a predetermined amount of time regardless of vehicle demand. Vehicle sensors are not required at these intersections because the system runs on a set timer rather than responding to the presence or absence of cars at the stop bar. Synchronization between signals is possible with the pre-timed mode; however, this method is very inefficient in terms of mitigating traffic or serving the needs of commuters and is not recommended.

Coming in as the polar opposite of the pre-timed mode is the actuated mode. In the actuated or “free” mode, there are no timing plans or synchronization between lights.

Each signal gets input from its own sensors and changes signal indication (i.e., the color of the light on the signal head) in a sequential fashion, regardless of what other signals on this main route are doing.

That is, with actuated signals, each intersection is something of a “first come, first served” affair: green lights and red lights are distributed according to the presence or absence of cars detected by the sensors at each individual intersection.

The advantage of the second mode, actuated mode, is that delay—that pesky wait time—on the side street is minimal during periods when traffic flow is light. The disadvantage is that delay experienced at the intersection as a whole will increase as motorists on the main street will need to stop while vehicles on the side street are being served. Also, there will not be any synchronization between signals. This lack of coordination will cause a substantial increase in stops, vehicle emission, delay, and fuel consumption. Thus, while isolated signals may effectively operate in actuated mode, it is not efficient to operate a string of signals in actuated mode.

The final and most efficient option is the synchronized mode. In this mode, the signal rests in green for the main street unless vehicles are present in the side street. This design takes into account the greater volume of traffic travelling through main streets and distributes more “go” time to that thoroughfare. Often, agencies may not install sensors on the main street because the signal will always revert to the default of giving green time to vehicles travelling on that street. The assumption is that more vehicles will always be present on the busier corridor.

Additionally, it is possible to synchronize multiple signals in an arterial in this mode, thereby allowing even greater customization for the needs of commuters along that route.

The Holy Grail every traffic engineer seeks is an efficiently installed and maintained system that allows for flexibility depending on changes in traffic patterns; thus, the synchronized traffic signal is the preferred option for effectively mitigating traffic congestion in city driving conditions.

Synchronizing semi-actuated signals allows whole movements of vehicles along a specific route to travel in what are called “green tunnels.” A green tunnel is a passageway of green lights enabling a group, or “platoon,” of vehicles to travel uninterrupted by congestion-causing red lights. Moreover, all signals that are synchronized must have the same cycle length. The cycle length is defined as the time it takes the timer within the controller to turn 360 degrees. In terms of what you see as a motorist, a cycle length is the time it takes to move from the beginning of green light to the end of a red light for your main street. Within that duration, the controller is required to sequentially serve all movements that have a demand. While this information may seem technical, we’ve all seen it in action. In reality, where an intersection fails to serve all movements sequentially—that is, give each direction of traffic its share of green lights—the resulting chorus of car horns would alert you of the lapse.

The cycle is further divided into “splits,” where splits are the percentage of a cycle allocated to a particular vehicle movement. Think of it this way: at an intersection of a main thoroughfare and a smaller side street, the main road is going to get the larger “split” of the cycle or the larger cut of green time. There is also one fixed point in the cycle that can be considered as a baseline and referenced. Offsetting this fixed point from one intersection to another synchronizes signals. If you’ve ever sung a tune like “Row, Row, Row Your Boat” in rounds, you can imagine the first singer as establishing the baseline upon which the other singers find their rhythm and melody. Much like when singing in rounds, synchronizing traffic signals in this fashion allows for a more complex, harmonious flow of traffic.

How Signals Communicate

To delve even deeper, traffic signals should be interconnected to form a network to ensure optimal performance.  Since roadways already function as a network, it makes sense for the technology responsible for directing traffic on these roads to communicate the same way.  Traffic issues don’t occur in isolation; if they did, we wouldn’t need to listen to the traffic reports during our morning or evening commutes.

Read an Engineer’s Perspective on the Signal Communication Problems

Traffic runs best when signals are interconnected and work together in a synchronized manner. Common media used for interconnection include wireless, fiber-optic cable, and twisted pair copper conductors. Often, this communication network covers the entire city and terminates at the office of the traffic engineer. Interconnection provides the engineer with remote access to the signal but synchronization is not perfect. Nevertheless, the overall effect of networking signals maximizes the efficiency of signal performance.


We hope you’ve begun to understand some of the technical reasons behind the difficulty of optimizing traffic signals.  The foundational equation behind most of the software models is flawed, and furthermore, the process of synchronizing the signals based upon those flawed equations is itself a time consuming and expensive endeavor. 

Since synchronizing traffic signals in this traditional manner is so inefficient, between 70 and 90 percent of traffic signals in the United States are not synchronized.  In fact, the National Transportation Operation Coalition grades U.S. traffic signal operation a grade D. 

However, it’s not the engineering limitations alone that earn us such a dismal grade.  Rather, a number of social and political factors prevent traffic engineers and city planners from making significant and technologically feasible improvements to traffic signal operation.  I will explore these limitations in greater detail in later blogs. For now, read more on the latest technology used for traffic control at www.rhythmtraffic.com.

Bo LaisTraffic Signals: The Troubling Truth

7 Traffic Signal Myths Debunked


Have you ever wondered how we process traffic signal information? It all starts with our early driving experiences and actually, over time, we learn to automatically block out traffic signals during our daily commute. That is, we block out the signals until we get caught at lengthy, numerous red lights over a relatively short distance. At that time, our focus then turns to the nuisance they cause – long delays to our final destination, road rage, and misconceived notions about the benefits of traffic signals (or lack thereof).

Click here to read about Oscar’s story.

In reality, the purpose of traffic signals is to solve traffic conflicts. We all want to be in the same place at the same time, but this would only lead to accidents, severe traffic jams, and ultimately, chaos.

To help you and those motorists out there, there are a number of preconceived ideas about traffic control that are absolutely incorrect and lead to frustration and unnecessary stress. I’d like to share the 7 myths that motorists actually believe about stoplights and other traffic signals.

Myth #1: The Flasher. If you flash your car’s high beams at a stoplight, it will turn from red to green more quickly.

Reality: Traffic light sensors do not detect headlights; they use other means to detect traffic at a light. Emergency light sensors read encoded and proprietary infrared signals from special emitters installed in emergency vehicles.

Myth #2: The Pusher. If you push the pedestrian crossing button multiple times or in a set pattern, you can trigger a green light faster.

Reality: While many of us are guilty of pushing the cross button over and over, it has no impact on how quickly the signal changes. When you push the button, the event gets recorded in the memory of the traffic signal controller (just as if you push an elevator button). This signal is then used to time the light change, nothing more.

Myth #3: The Weight-Builder. The amount of weight present at an intersection triggers a green light.

Reality: The weight of a vehicle has nothing to do with triggering a green light indication. Vehicle presence is detected by inductive loop technology, which works on the principle of electromagnetic induction, and all that is necessary is a vehicle having sufficient iron in the metal for detection and stopping over the inductive loop which signals the traffic controller that there is traffic waiting at the intersection.

The only vehicles potentially affected may be motorcycles or mopeds, but this can be overcome by drivers pulling near the corner of the lane near the stop bar painted at the intersection.

Myth #4: The Unseen. Traffic lights are changed by tripping an invisible curtain that covers only a section of the lane.

Reality: Vehicles trigger the inductive loop (see Myth #3), and as long as they have sufficient metal and stop in the right spot – just before the stop bar, the thick white line painted on the pavement that signals to motorists where they should stop in order to be effectively detected by the traffic controller.

Stop too far past or before the bar and the pavement sensors can’t detect your presence. As a result, motorists who do not stop at the stop bar generally end up waiting longer at intersections!

In order to be detected, motorcycles and bicycles also must stop before the stop bar. The in-pavement detectors are most sensitive at the corners. So, motorcycles have a better chance of being detected if they stop at the corner of the lane just behind the stop bar too.

Myth #5: Remote Controlling. You can turn the stoplight green through the use of a universal television remote.

Reality: You cannot program a remote with a special code in order to change traffic signals. This myth stems from an Internet spoof and holds no truth. Sensors associated with preemption systems are programmed to only detect certain infra-red signals from emergency vehicles and cannot be fooled or tricked into activating a green light for passenger vehicles; and for good reason.

Imagine the chaos if every impatient driver with access to a Radio Shack, took it upon himself to direct traffic according to his whims!

Myth #6: Big Brother Is Stopping You: Governments or cities purposely implement policies that do not allow traffic to efficiently flow through intersections.

Reality: Most traffic lights are poorly timed and inefficient because transportation agencies don’t have the personnel or financial resources to update their timing plans or implement newer traffic technologies that could reduce delay at intersections. Without experienced personnel or money for updates and improvements, cities are unable to improve the efficiency of their traffic control systems and motorists, by default, are stuck wasting time and fuel at red lights.

Myth #7: The Safety Patrol. Traffic signals always reduce collisions.

Reality: The key word here is “always”. Traffic signals do help prevent collisions, but since only 40% of collisions occur at intersections, and drivers often get into accidents by trying to beat a red light or disobeying traffic rules, the truth is that poorly timed signals will not eliminate human actions, and therefore, will not eliminate all accidents.

Nevertheless, optimizing traffic signals to mitigate traffic conflicts is in the best interest of everyone. Coordinating traffic signals can reduce driver frustration, cut down on the number of cars running red lights, and decrease the number of traffic accidents occurring at our intersections.

Bottom line:
Motorists form their own opinions based on urban myths about traffic signals and controls. Our job, as traffic experts, is to minimize the number of traffic aggravations experienced by motorists.

The ultimate goal is signal optimization for each and every thoroughfare – this can be accomplished through synchronized traffic signals, vehicle detection systems, and communication between intersections. Learn more about the latest technology used for traffic control at www.rhythmtraffic.com

Bo Lais7 Traffic Signal Myths Debunked