what are these cables that protude from lamposts

[tom2019]

Sometimes I see two cables laid out across the road in pairs.

wtf are they?

[Mr Pies]

Traffic density monitoring?

[Puddenchucker]

For counting traffic.

[98elise]

They measure speed, volume and direction of traffic, for surveys.

[Monkeylegend]

Electricity for the light bulb.

[Teddye4687]

I've always wondered if thy monitor speeds. Tin foil hat, but I expect to see camera vans based on results.

What if someone were to space the lines a little further apart?

[TheHeretic]

They are tiny little speed umps for tiny little cars that ants and other insects drive.

[Strawman]

Teddye4687 said:

I've always wondered if thy monitor speeds.

They don't, to do that you'd need to know the wheelbase of the vehicle that's crossed over them which obviously varies quite a bit between a smart car and a bus.

[Spitfire2]

Strawman said:

They don't, to do that you'd need to know the wheelbase of the vehicle that's crossed over them which obviously varies quite a bit between a smart car and a bus.

When there are 2 cables why would wheelbase be relevant? They know the distance between the cables.

[r1ch]

I've often wondered this too, so are they just to measure volume of traffic throughout the day then?

[grahamr88]

Strawman said:

They don't, to do that you'd need to know the wheelbase of the vehicle that's crossed over them which obviously varies quite a bit between a smart car and a bus.

No you don't, that's why they're in pairs. The front wheels will go over one then the other, and the back wheels will then do the same.

[Strawman]

Spitfire2 said:

When there are 2 cables why would wheelbase be relevant? They know the distance between the cables.

There are two cables to tell which side of the road the vehicle was on, which cable was driven over first tells you that. Some traffic planning person was on here before confirming they are for monitoring traffic density/flow not recording individual speeds, which they aren't set up to do.

[Zyp]

grahamr88 said:

Strawman said:

They don't, to do that you'd need to know the wheelbase of the vehicle that's crossed over them which obviously varies quite a bit between a smart car and a bus.

No you don't, that's why they're in pairs. The front wheels will go over one then the other, and the back wheels will then do the same.

What if someone on a unicycle goes over them?
Will it send the black box into a tizzy, waiting for the rear wheels....?

[Teddye4687]

Strawman said:

They don't, to do that you'd need to know the wheelbase of the vehicle that's crossed over them which obviously varies quite a bit between a smart car and a bus.

I was thinking something simpler - how long it takes to hit the second line from hitting the first (wheelbase bears no impact on this speed measurement)

[EddieFelson]

Teddye4687 said:

I was thinking something simpler - how long it takes to hit the second line from hitting the first (wheelbase bears no impact on this speed measurement)

Wheel size would

[Puddenchucker]

http://www.clearviewtraffic.com/golden-river/produ...

[Dogwatch]

Teddye4687 said:

Strawman said:

They don't, to do that you'd need to know the wheelbase of the vehicle that's crossed over them which obviously varies quite a bit between a smart car and a bus.

I was thinking something simpler - how long it takes to hit the second line from hitting the first (wheelbase bears no impact on this speed measurement)

That's what the constabulary used to think too in simpler times when they lurked nearby with a meter connected to said box and radioed the 'stopper' down the road to haul in the miscreant.

Spotting two black lines across the road raised two questions - was it a speed trap or a traffic counter?

[Teddye4687]

EddieFelson said:

Wheel size would

How? If it takes 2 seconds between contact, you're travelling at (Distance/Time), regardless of wheel size..

[Puddenchucker]

Dogwatch said:

Spotting two black lines across the road raised two questions - was it a speed trap or a traffic counter?

IIRC 2 tubes was a traffic counter, 3 tubes was a speed trap.

[wst]

Two wires so they know which direction the traffic is going...

3 wires is a speed trap. Which is kind of handy when it comes to those blasted Truvelos - they can't see you until you're on the 3 lines (when they do the actual speed measurement) so don't be speeding over those 3 lines and you're fine (I did a lot of research after suspecting I triggered one on the A1 northbound once...)...