Forward facing cameras

[Dakkon]

If you slow down before the 3 lines in the road can they still get you or is their range longer than that?

[egomeister]

Truvelo cameras are set off by an inductive loop ahead of the white lines - you should be able to see this cut into the road (look for a strip of sealer on the tarmac) I can't remember the distance but its not too far. The lines are just a verification of which car is speeding (ie for dual carriageways)

If you were slowed down a reasonable amount before the lines you should be fine.

[smeggy]

Truvelo sensors use pressure sensitive peizo strips (not induction loops) to measure vehicle. The 3 lines are the corroborative speed measurement which must match the sensor measurement (confirmation).

In theory (if your car could brake hard enough) you could trigger the camera (via the sensor strips) but your wheel won’t have reached the while lines as the flash goes off (delayed for corroborative measurement); hence the corroborative measurement would not match the sensor measurement.

However, you won't be able to brake hard enough; you'll need at least -2G at ~30mph (more G at higher speeds).

www.truvelouk.com/secondaryspeedchecks.phtml

[7db]

smeggy said:

However, you won't be able to brake hard enough; you'll need at least -2G at ~30mph (more G at higher speeds).

For constant acceleration:-

v^2 = u^2 + 2as

s = 1.8m
u = 35mph = 15.6mps
v = 30mph = 13.4mps

=> a = -1.8g

Average speed: sensor -> line is 32.5mph

[Dakkon]

Well I guess I shall have to wait and see, was driving to work this morning and for the first time in ages the A339 from Newbury to Basingstoke was clear of slow lorries, trucks, buses and just slow cars, so was just enjoying the car and the road and completely forgot about the cameras just outside of Basingstoke, stood on the brakes, but no idea if it was too late.

Ah well, thanks for the replies.

[smeggy]

7db said:

=> a = -1.8g Average speed: sensor -> line is 32.5mph

I agree with your maths; however, I’m under the impression that the secondary speed must be within 10% of the primary measurement, so I worked on the assumption of an average speed of 31.5mph (lowest speed of 28mph), hence my G level works out to be higher



EDIT: the distance from the first and last white lines to the last sensor strip are 0.9 and 1.1 times the distance from the middle line to that sensor strip.

Edit2: I just realised: a driver could also be slowing down between the sensor strips. If the two pairs of sensors don’t require an exact speed match, it could halve the amount of deceleration required to render the secondary measurement erroneous, probably to 1.1 – 1.2G (I can’t be bothered do the exact maths); that’s within reach!!!



>> Edited by smeggy on Friday 17th March 14:46

[smeggy]

Dakkon said:

Well I guess I shall have to wait and see, was driving to work this morning and for the first time in ages the A339 from Newbury to Basingstoke was clear of slow lorries, trucks, buses and just slow cars, so was just enjoying the car and the road and completely forgot about the cameras just outside of Basingstoke, stood on the brakes, but no idea if it was too late.

You should be alright if you didn’t see a bright pink (strictly speaking: magenta) flash.