Safe Speed Forums

Boys and girls, take pity on us. In Sydney, on a short, sharp incline away from one of the tributaries of the Harbour there are two speed cameras, perhaps 150m apart. Recently, tickets were served on a number of buses for alleged breaches of the 60km/h limit (one bus was 'caught' at 87km/h). A TV station got wind of the problem and put one of its camera crews on a bus and tried to reproduce the 'offence'. The best they could get out of the bus (unladen, except for driver, camera and crew): 56km/h. Mutiny was threatened and the NSW Roads and Traffic Authority, under mounting pressure, agreed to test the more zealous camera. They found ... well, prepare to suspend all disbelief and read the explanation here ...
http://www.news.com.au/story/0,10117,12 ... 62,00.html

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Bob, Sydney

Hi Bob,

Welcome.

I've been discussing this case in an email list...

-------- Original Message --------
Date: Sat, 19 Feb 2005 04:17:21 +0000
From: Paul Smith <psmith@safespeed.org.uk>

Hi all,

Is this a radar based camera?

We know for sure that flat vibrating panels (like the back of a bus)
frequently cause doppler radar speed meters to misread.

In the case where a bus engine is under heavy load - as when climbing a hill -
the engine will be the source of considerable vibration.

So if it's a radar based camera, I think that's case solved.
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-------- Original Message --------
Date: Mon, 21 Feb 2005 10:23:02 +1100
From: "Bruce Josephs" <josephsb@cyber.net.au>

Your argument holds true where it is a speed camera using radar.

However, the Speed Cameras on Spit Hill use the piezo sensors in the
ground instead of radar. You can see the three lines on the road where
the vehicles pass. The radar calculates the difference in time over the
distance passed. There is no radar used.

Instead what is probably happening is that the bus is creating
sufficient vibration to cause the piezo sensor to think that the bus has
passed the second and third sensors prematurely.

The question that needs to be asked is that if this can happen for
buses, what stops it from happening for trucks and other vehicles in the
vicinity of larger vehicles. The answer is probably nothing.

It is interesting to note that the RTA is willing to suspend the fines
for bus drivers (employed by a government dept who were going to strike)
but not a garbage truck that has proven that it could not have made the
speed indicated.
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So it's possible that the newspaper explanation is more or less correct.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I have seen it suggested either here or elsewhere that the sensors are only good for a couple of years at most before they start to give false readings.

So are these similar/same to Truvelo cameras?