Traffic Signals and Intersections: An Innovative Approach

Today’s blog post is sponsored by Horiba – a leading manufacturer of spectroscopy and material analysis solutions.

Most people have experienced the frustration of traffic signals. The lights change at the wrong time, leaving cars in the middle of the street. Or it is the middle of the night with no one around, and the red light still lasts a minute too long. Besides the delayed time for drivers, inefficient traffic systems can lead to additional greenhouse gas emissions, since idling cars release up to 30 million tons of carbon dioxide per year, which is about 6 million tons of fuel. A smart traffic light system could alleviate these types of issues.

In the early 1900s, when cars were becoming popular in the United States, there were no traffic lights or signs, leading to confusing and dangerous situations. In the 1910s, a traffic light with just red and green lights was introduced, but the reaction time of drivers led to many accidents. The first three-light traffic signal was invented in 1923 by Garrett Morgan and this design has stayed about the same since then. The two-way traffic signal is shown in the image below next to the modern, three-way signal. 

A two-light traffic signal (left) and a modern three-light signal (right). Photo courtesy of artsy.net.

Modern Traffic Signals 

Traffic lights have evolved since this basic system. Some use cameras, radar systems, sensors, and pneumatic road tubes. The road tubes are filled with air, and when a car drives over it, an air switch is closed, producing an electric signal. This not only helps with traffic lights but also with analyzing how many cars and the types of cars which drive on a road. The issue with some sensors is that they do not account for travelers other than cars, such as bikers or walkers, and do not perform accurately in inclement weather. 

There are many types of sensors that exist at traffic lights, and all aim to make the traffic flow as efficient as possible. Infrared sensors can tell when a car is in an intersection. Active infrared sensors emit energy into the traffic area, and when a car drives by, the sensor sends a pulse to the traffic light. A passive infrared sensor is an opposite of active sensor, it picks up on energy from other cars. Both of these alert the light to change when a car is sensed. Microwave sensors use electromagnetic energy instead of infrared, but they still detect traffic and communicate with the signal. Microwave sensors are cheaper but are not as robust as other sensors. 

Sensors that worked using energies were discussed above, but using motion is an upcoming technology in traffic flow with doppler sensors. Doppler sensors not only sense motion but can also count the number of vehicles that drive through. This replaces cameras, other sensors, and pneumatic road tubes. These doppler sensors can also sense pedestrians, making roads safer for everyone. 

Sensors and detection methods are not only used at traffic lights, but they can also be installed anywhere on roads. This makes the traffic light process information before the vehicles even come into the intersection. Ultrasonic type traffic sensors are placed above the cars, which transmit ultrasonic waves and measure traffic volume. These sensors work by transmitting sound waves. The sound waves are then reflected, allowing for the quantity of traffic to be calculated. Doppler ultrasonic sensors work similarly, but they can detect both the speed of the car and the direction. These are most often used for intersections with a main road and less trafficked side road. The doppler ultrasonic sensor detects the car on the side and changes the signal to a green light.

Laser doppler sensors can be found here.

Smart Traffic Technology

The idea of a “smart” traffic system is not new. In Australia in 1975, the Sydney Coordinated Adaptive Traffic System (SCATS) was developed to assist with the congested traffic in Australia’s cities. Currently, SCATS works by processing inputs from both drivers and pedestrians. Induction loops are underground and can detect vehicles, while pedestrians push the buttons on the light. This data is quickly sent to a larger database which takes into account the surrounding traffic. The light then changes based on the analyzed information.  

Surtrec is another, more recent development in the “smart” traffic world. First, cameras, radar, and sensors detect the current state of traffic. Then, communicating with nearby traffic signs, uses artificial intelligence to determine the best timings for signal changes. This system has decreased travel time by 25%, due to fewer waiting times and fewer times requiring a speed change. These also lead to a 20% reduction in carbon emissions. This system can sense traffic and get real-time weather updates. The light can then factor in the slower traffic due to things like snow. The image below shows how traffic signals can be constantly communicating with the vehicle pattern. 

Vehicles traveling through a smart traffic signal system. Photo courtesy of cleantech.com.

Using Sensors to Understand Traffic

Urban planners have the job of determining where traffic signals should be. Using optical beacons is an innovative way researchers at the Institute of Transportation Engineers have found to trace traffic patterns. In a paper titled, “Using Optical Beacon Data to Investigate Driver Route Choice Behavior”, optical beacons are utilized to determine which routes drivers are more likely to take: a main route, and a less-trafficked second route adjacent to the main road. Optical beacons are placed at two different points and can measure the time it takes for vehicles to get from one place to another. These beacons use infrared radiation to detect cars. In this specific study, the reasoning behind why certain routes were taken was qualified. Drivers mostly took the main route, but the secondary route was taken based on the traffic on the main road. The number of turns also influenced if the secondary route was taken. Overall though, the travel time between the two routes was similar for all seven areas studied. These optical beacons can be used in busy cities with congested roads to determine if traffic signals need to be added based on which cars take which routes. For example, cars may be taking a side road since there are only stop signs, not traffic lights. Planners may need to reevaluate this area if the stop sign intersection gets too congested. 

Currently, most urban areas have an extensive traffic efficiency plan; however, most commuters will have issues with congestion and wait times. With these “smart” traffic systems in the works, travel time and carbon dioxide emissions could decrease and cars would smoothly drive down any road.