New Swiss radar

[Brian Ellis]

http://www.youtube.com/watch?v=-eS5CtV2s2c (commentary in French)

This radar not only detects the guy speeding, in any lane, but can differentiate between types of vehicle with different limits, such as heavy goods vehicles, trailers etc. The secret is a detector mounted on the barrier rail which determines the type of vehicle and the lane it is using and transmits the info to the radar which adjusts the limit at which it flashes, automatically. In the example shown, the big truck in the nearside lane is being flashed while the cars in the two lanes nearer the camera are travelling faster legally. To avoid contests, the doppler radar triggers the flash above the set speed for the type of vehicle, but the distance moved between the two flashes at a fixed interval is used to calculate the speed a second time.

In the opening sequence (after the commentator) the old type radar box is shown and then the new ones, which cost only half the price of the old ones. In the Canton of Vaud, they have installed 20 such boxes between the border with Geneva and Lausanne, about 45 km of highway. The accident rate has since dropped by over half (they don't say how much they've raked in with fines!!!!), but it's a foolhardy driver who exceeds 120 km/h along that stretch today.

[Gurm]

The big question is, do they have the same weakness as previous cameras?

On the first-ever episode of Top Gear they proved that IF:

1. You have a REALLY fast car.
2. You have a tame racing driver.
3. You get your tame racing driver to drive your really fast car past a speed camera at a velocity in excess of 170MPH.

THEN The camera doesn't even know you're there.

This is at odds, however, with the usual urban myth - that driving "fast enough" causes the camera to only take ONE picture of you instead of two, thus rendering the evidence invalid. That was disproven at all speeds up to 150MPH.

http://www.youtube.com/watch?v=-eS5CtV2s2c (commentary in French)

This radar not only detects the guy speeding, in any lane, but can differentiate between types of vehicle with different limits, such as heavy goods vehicles, trailers etc. The secret is a detector mounted on the barrier rail which determines the type of vehicle and the lane it is using and transmits the info to the radar which adjusts the limit at which it flashes, automatically. In the example shown, the big truck in the nearside lane is being flashed while the cars in the two lanes nearer the camera are travelling faster legally. To avoid contests, the doppler radar triggers the flash above the set speed for the type of vehicle, but the distance moved between the two flashes at a fixed interval is used to calculate the speed a second time.

In the opening sequence (after the commentator) the old type radar box is shown and then the new ones, which cost only half the price of the old ones. In the Canton of Vaud, they have installed 20 such boxes between the border with Geneva and Lausanne, about 45 km of highway. The accident rate has since dropped by over half (they don't say how much they've raked in with fines!!!!), but it's a foolhardy driver who exceeds 120 km/h along that stretch today.

[Brian Ellis]

In the first place, Jeremy Clarkson may be a good journalist with a sense of humour, but he knows and understands bugger-all about technical matters (perhaps except what he was told by someone in the work-up to a programme). Actually, Richard Hammond knows more in his little finger nail than JC has in his cranium!

Since that programme was recorded, many years ago, don't you think that the technology has advanced just a little? He used a microwave unit (possibly K-band), which is now obsolescent. This includes the bandwidth of the frequency differential amplifier, which was the limitation on the old systems. The modern ones use two types of doppler radar - well, to be accurate, one type of radar at infra-red frequency (collimated laser), the other being ultrasound. This is how they are able to differentiate between vehicles in different lanes, as the responses are very different, because of the difference in the velocity of propagation between the laser at c. 300,000 km/s and acoustic pressure waves at c. 1,100 m/s. This also enables the software to make cos Θ corrections for the angle of attack, because of the time difference between reception of the two reflected signals.

Anyway, I'm quite sure that the modern ones will detect anything up to a jet aircraft! I know a Swiss driver in a Ferrari was recorded at 282 km/h (~176 mph) on a French motorway (130 km/h limit) and I've heard a rumour about a TX driver caught at 224 mph, but have not substantiated that.

Note that there are three types of camera. The conventional doppler one flashes once only. The "cross-the-road" type flashes twice, once when entering a collimated laser beam and once when leaving it. As the width of the beam is known at the distance, the time interval between the flashes is recorded and the software includes conversion of time to speed. The third type is when the two flashes are at a fixed interval.

[Fat Tone]

Actually they (TG) redid that test in the last-but one series. IIRC they had to get up to ~187MPH before that particular camera didn't go off.

On a slight tanget, its now ~4.5 years since I got caught by one. The points are valid for 3 years, they have to stay written on my license for 4 years, and Why T.F. do I have to declare it to insurers for 5 years?