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Smile, You’re On… Speed Camera

Love them or hate them, speed cameras are to stay. Actually, I don’t think that anybody loves speed cameras. Most of us would love to do what Rowan Atkinson does in “Johnny English” – fire a missile at that thing that’s just snapped us and blow it to smithereens. And in case you’re wondering whether this writer has recently had a wee picture of their car taken at an unexpected moment and is feeling grumpy about it, I haven’t.

The idea of speed cameras around the place is a way of keeping speeds down. We all know the horror stories and the physics about high speeds and high-speed crashes. No matter how many high-tech active and passive safety devices your new car has, once you get a certain mass involved at a certain speed (sorry, make that velocity – I was listening in your class back at high school, Mr Cook), the forces involved and the law of the conservation of momentum mean that there’s going to be one heck of a bloody mess. Literally bloody. However, even knowing about what will happen if you crash at speed, some people still do it. Hence speed cameras and speed traps – if the idea of having your internal organs reduced to pile of mince doesn’t put you off heavy-footedness, possibly the idea of paying out will deter you.

One thing that can be said in favour of the unmanned (unpersonned? unstaffed?) speed cameras is that they are unbiased. If a cop is manning the radar machine and taking licence plates, there is a risk that they will be biased by the style of car being driven. Hot sports car such as a Mitsubishi Evo or a Porsche 911 whizzes past? Whip out the radar gun and see what it’s doing. Little Mini Cooper or VW Beetle whips past driven by a silver-haired lady? Ignore it – even though said Mini or Beetle is quite capable of exceeding the speed limit.


Speed cameras work on a fairly simple principle of physics – one that was taught later on in the year back in Mr Cook’s class. It’s similar to the echolocation used by bats and dolphins. The radar emits an electromagnetic signal, which bounces off the car, like that squeak by the dolphin bouncing off a fish. In a classic radar camera, the receiver on the apparatus measures the frequency that the wave comes back at, which is changed thanks to the Doppler effect (it’s blue shifted). The difference between outgoing frequency and incoming frequency tells the doohickeys inside the camera how fast the car is going and triggers the camera. The camera picks up a picture of your car and your licence plate, and you get hit in the wallet. A speed camera of the classic radar type can only pick up vehicles going in the direction of the radar, so if you’re going at right angles to it, you won’t get picked up.

Can speed cameras pick up things that aren’t cars (and vans, motorbikes, etc.)? Yes, they can. The story about the UK cops picking up a NATO fighter jet on the radar, putting said fighter jet on alert and ready to put a missile into the radar system, is just a rumour, but speed cameras can pick up other vehicles. There have been cases of urban speed cameras picking up cyclists, especially if the cyclist is a fairly fit person on a modern bike with a tailwind going down a slope.
Many people argue that speed cameras are just a way of filling up the police department’s coffers. However, they do keep speeds down, as folk have a tendency to go lightly on the accelerator if they think that there’s a speed camera in the area. There was a (true) story from New Zealand about a guy in a rural area who got fed up with the hoons speeding past his place, so he rigged up a fake speed camera involving a couple of boxes and a pumpkin in the open boot of a white stationwagon that looked like the Holden Commodores beloved by the NZ Police. The speeds of passing cars dropped considerably when this was parked on the road side.

And now it’s confession time. When this writer was a uni student, we thought it was a hoot to be a fake speed camera. This involved parking up on the side of the road in an area where speed cameras sometimes lurked after dark. Switch the lights off but when a car goes past at a reasonable clip, waggle the controls to make the headlights go on and off quickly. All our victims would see was the flash and a parked stationwagon, and we’d snigger as the brake lights flared and the tyres squealed as some poor sucker thought they’d been clocked. Bet they spend several weeks wondering when the nasty letter was going to come in the mail. I don’t know what the cops would have said if they saw us – were we contributing to road safety, cheating them out of bagging a fine or simply pulling a harmless prank that was better than some of the other things uni students got up to?


  1. Bob Rona says:

    Herein lays the real problem.. If they want to really stop people speeding, With the next rego payment, everyone gets a GPS controlled device that is linked to the vehicles cruise control system, and as most decent GPS systems KNOW what the speed limit is in any given area, that unit can then Govern Limit the vehicles speed .
    When vehicles don’t have a cruise control system , it then makes a simple instillation of such unit a great benefit to the vehicle, and a controlling one when married to the Governor Unit.. and before anyone complains about ‘Big Brother’ .. what’s more important, Saving Lives and property, or the revenue raised???
    Maybe this sounds too simplistic, but most great ideas generally are !


    April 19th, 2012 at 11:45 am