Polish scientists create autonomous road signs with built-in Doppler radar

Poland is pioneering new road signs that combine a series of sensors to monitor road traffic and conditions to warn drivers of road hazards.

Researchers are building ‘intelligent’ highway signs to track traffic volume and warn drivers of potential hazards in real time as part of a national project called INZNAK.

The boards also measure weather conditions and use different types of radar, including acoustic vector sensors (AVS), which are traditionally used for underwater applications.

AVS reads reflected sound waves and calculates traffic on a specific stretch of highway, which can then be relayed to drivers to warn of congestion.

Polish researchers say the technology would allow traffic signs to detect constant traffic on the road and use this, and a host of other data, to warn drivers of potential dangers that lie ahead.

WHAT IS THE DOPPLER EFFECT?

The Doppler effect, or Doppler shift, describes the changes in frequency of any kind of sound or light wave produced by a moving source relative to an observer

The Doppler effect is a well-understood physical phenomenon also seen in astrophysics as the universe expands and causes ‘redshift’, but it is more common in sirens.

For example, when a blaring ambulance or police car shoots past with its sirens on, they appear high as they approach you and then lower as they race past.

This is due to the compression of sound waves as they get closer, and they stretch as they get further away.

A stretched sound wave has a longer wavelength, and therefore a lower frequency, resulting in a progressively lower pitch.

The smart road signs are also equipped with a built-in Doppler radar – a specialized radar technique based on the Doppler effect.

Doppler radar is already used along roads to read how fast cars are driving and to tell drivers to slow down when they are above the speed limit, as well as in police speed guns.

In smart road signs, Doppler radar measures the speed of objects such as cars or precipitation droplets on the road.

When deployed, an entire network of signs will also communicate via vehicle-to-everything (V2X) technology – a form of Wi-Fi designed for fast-moving objects that allows smartphones and cars with Bluetooth to talk to each other.

The whole project is funded by the Polish National Center for Research and Development, the country’s public agency for scientific innovation.

Principal project scientist Andrzej Czyzewski, of Gdansk University of Technology in Poland, describes his work at the 179th meeting of the Acoustical Society of America, which will be held virtually December 7-10.

‘We can calibrate an acoustic vector sensor [AVS] so it can be used to measure traffic volume on the highway and count vehicles by analyzing the noise they emit as they pass by, ‘Czyzewski said.

“When implemented successfully, the devices we developed will communicate with each other in V2X technology and actively respond to the traffic situation, suggesting the drivers the speed appropriate to the situation.”

This technology was about to be rolled out earlier this year, “but the pandemic has slowed production,” Czyzewski said.

INZNAK road signs would communicate with each other about data such as weather conditions, road surface conditions, traffic volume, the average speed of vehicles and detected road events such as accidents or congestion.

Each board would run an algorithm to process that data and calculate the current status of an assigned portion of the road and driving conditions.

As part of this project, the signs are made so that they can be placed on a mobile stand or hung above the road.

They show updated speed limits that are automatically determined by a mini computer within the road sign.

AVS technology is used to measure movement and pressure changes associated with a sound wave.

This principle, applied to traffic, can reveal the direction in which a sound wave is traveling and how many sound sources are nearby.

AVS is combined with Doppler radar, which is based on the principle of the 19th century Austrian physicist Christian Doppler.

Smart road signs combining Doppler radar and video with acoustic and weather sensors can track traffic volume and warn drivers in real time of dangers ahead

Illustration of the Doppler effect. Motion changes the frequency of the sound wave based on the direction of movement of the source. That’s why ambulance sirens sound lower after they pass us

The Doppler effect describes the changes in frequency of any kind of sound or light wave produced by a moving source with respect to an observer.

The effect explains why the car’s horn sounds lower after passing than when approaching, for example.

Doppler radar systems can provide information about the movement of targets and their position.

A Doppler radar system sends out pulses of radio waves aimed at a target, such as a car.

It then measures the difference between the transmitted pulse and a received echo to determine the movement of the target.

INZNAK road signs will be equipped with both AVS and Doppler radar as both have advantages over the other, Czyzewski said.

Although the acoustic vector sensor – the epitome of acoustic radar – has a lower accuracy than the Doppler radar in vehicle counting and is unable to measure vehicle speed with the same precision, it has significant advantages over Doppler sensors ‘said Czyzewski.

The main advantages are that AVS does not emit signals and is not sensitive to electromagnetic interference like Doppler sensors.

AVS also makes it possible to analyze audio signals to provide an assessment of road conditions – whether wet or dry.