Can You Drive Fast Enough to Avoid Being Clocked by Speed Cameras?

(Photo: Elliot Brown)

In some jurisdictions, governments set up cameras along roads to track how fast cars move. If a car is traveling over the speed limit, it snaps a picture of the license plate on it. A computer then fines the owner of the car.

Would it be possible to drive so fast that the camera wouldn't be able to take a picture of your license plate? Please don't to do it. But, yes, it is hypothetically possible.

Physics students at the University of Leicester in the UK determined that if a car traveled at 119 million miles an hour--that's about 1/6 the speed of light--the plate would be unreadable to a speed camera. That's because of the Doppler Effect. As the car moved at that velocity, light from it would shift toward the red end of the spectrum, rendering the car undetectable. Phys.Org explains:

Their calculation is based on the Doppler Effect – the physical effect where the frequencies of light or sound waves emanating from an object increase or decrease when it moves towards or away from you.

This effect is at work when you hear an ambulance – its siren will appear to lower in pitch as it drives past you.

With light, this process creates "red shift" – where the frequency of light from an object travelling away from the observer is shifted towards the red end of the colour spectrum. The faster an object is travelling, the bigger the shift in frequency.

This means it would theoretically be possible for the light from a fast-moving car number plate to be shifted out of the frequency range which speed cameras are able to detect.

-via VA Viper


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Yes, you can. I believe Mythbusters did it.

https://www.youtube.com/watch?v=t4pE1KBsWb0

That's below 300mph. ("The Beast can reach speeds up to 300mph.")

Camera shutters can only do something like 1/10000th anyway, so you should only need to calculate the worst case of the car sign being too blurry over that timeframe. If the car needs to move 1 meter for the sign to be blurry, it only needs to go 10000m/s - much slower than the redshift calculation.

I'm actually impressed that a car going 100m/s (sync times of 10ms) seems to work perfectly fine (that's 236mph).

With sync time I mean the time from measure to reaction to running the shutter and flash.

Also see the other Mythbuster episode where they tried to beat it with a street-legal supercar.
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This is a good point. I considered phrasing the headline that way, but decided to go with one that was punchier but less precise. Sometimes there is a trade-off.
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I found this rather disappointing. I don't want to be discouraging to upcoming students, but the paper amounts really to just plugging numbers into an equation, something on par with an intro level physics class homework problem. At best it seems to be an exercise in formating and the process for submitting a paper. There is a long list of reasons a speeding camera would fail to capture an image of a speeding car, most of which would be at much, much slower speeds, possibly in reach of a real car depending on the particulars of the camera. A review of previous attempts and discussion of multiple methods would be much more on par with something appropriate for a simple paper, and could still easily be done by a class of students by splitting up the methods between different students. I've seen class projects like that were before, that were a lot of fun for the students over analyzing something silly in great detail.
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