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Why a classic physics phenomenon could prevent future car crashes

Smart traffic signs will have their robotic eye and ear on you.

Originally Published: 
Vector of two car accident top view of vehicle collision on blue background

Cars are getting smarter every day — whether assisted by A.I. or equipped with advanced safety sensors like backup cams — but these advancements have done little to actually prevent traffic accidents. Around the world, 1.35 million people die as a result of roadway accidents annually.

Handing the wheel over to your autonomous vehicle is predicted to finally curb this trend, but the mainstreaming and wide distribution of these vehicles isn't coming anytime soon. Looking for a solution, scientists have set their sights on a new part of the driving experience to automate: traffic signs.

A team of researchers in Poland has designed a smart traffic sign that uses the Doppler Effect, a physics phenomenon, and video to detect everything from passing vehicle speed to road conditions. Unlike existing traffic sensors that simply record speed, these dynamic signs would warn drivers of impending accidents before they happen.

This research was virtually presented Monday at the 179th Meeting of the Acoustical Society of America.

How it works — To capture traffic patterns in real-time, these smart traffic signs rely on a two-tiered system of sensors. First, a Doppler radar is used to collect acoustic data of vehicles as they pass by individual signs.

This radar works by taking advantage of a simple, but powerful, physics phenomenon called the Doppler Effect. Essentially, as vehicles drive by these signs they squish sound waves in front of them while behind them the waves fan out more leisurely — kind of like what happens when you kick a blanket away with just one foot.

Using the Doppler Effect, these smart traffic signs can better predict traffic accidents.


These squeezed layers of air around the vehicle affect how the sound emitted from the car travels. As the front of the car passes, its sound will become more high-pitched (like the weeee of an approaching ambulance,) and when the backside passes it will become lower-pitched (like an ambulance's retreating ooooh.) This is the same acoustic sensation you might experience when listening to an ambulance speed away and it only becomes more accentuated as the vehicles' speed increases.

This acoustic doppler data is then further analyzed by something called an "acoustic vector sensor" (AVS) to create a more dynamic picture of traffic patterns.

"We can calibrate an acoustic vector sensor so it can be used to measure highway traffic volume and count vehicles by analyzing the noise they emit as they go by," study co-researcher Andrzej Czyzewski, said in a statement.

This traffic information can then be transmitted to motorists either as updated speed limits on the signs themselves — these will hang either above or beside the road — or using vehicle-to-everything transmission, which is a WiFi derivative that allows fast-moving vehicles to communicate with smartphones via Bluetooth.

A visual mock-up of what these smart traffic signs might look like on the road.


The advances — Using doppler radar to detect vehicle speeds is nothing new — it's the same tech that police speed guns use — but the researchers explain that their system has a distinct advantage over others when it comes to discouraging tampering.

While some doppler sensors use microwaves to make their measurements, which are susceptible to electromagnetic interference, the researchers say that their AVS uses passive monitoring and doesn't emit any signals that could be manipulated. More importantly, their sensor also enables the smart traffic signs to collect information about weather and the road condition (for example, how slick a road is), making its estimation of traffic hazards even more accurate.

What's next — Czyzewski and colleagues have only just presented their results at a conference and have yet to publish a full paper of the research. In addition to testing their traffic signs in the wild, another obstacle for the team to overcome will be the rollout of the vehicle-to-everything Bluetooth technology, which Czyzewski said is delayed because of the pandemic.

Abstract: Comparing traffic intensity estimates employing passive acoustic Radar and microwave Doppler Radar sensor. Andrzej Czyzewski (Multimedia Systems, Gdansk Univ. of Technol., Narutowicza 11/12, Gdansk 80-233, Poland, The purpose of our applied research project is to develop an autonomous road sign with built-in radar devices of our design. In this paper, we show that it is possible to calibrate the acoustic vector sensor in such a way that it can be used to measure traffic volume and to count the vehicles involved in the traffic through the analysis of the noise emitted by them. Signals obtained from a Doppler radar are used as a reference source. Although the acoustical vector sensor (AVS), being the embodiment of acoustic radar, has a lower accuracy than Doppler radar in vehicle counting and it is not able to measure the vehicle speed with the same precision, it has some advantages over the Doppler sensor. Namely, it does not emit any signals, it is not susceptible to electromagnetic interferences and it allows for further analysis of audio signals, such as assessment of the road surface state (e.g., wet/dry). The acoustic radar we developed is a new proposition of the acoustic method for road traffic monitoring. In addition, our research allowed a comparison of the efficiency of both methods, i.e., microwave and acoustic ones. [Project No. POIR.04.01.04-0089/16 entitled: “INZNAK – Intelligent road signs with V2X interface for adaptive traffic controlling” is financed by the Polish National Centre for Research and Development from under the EU Operational Programme Innovative Economy.]

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