revtothelimit - motorbike forum

Those black cables they put across roads. Are they just counters.? They've put a few up around here and an ex cop once told me they can check for speeding aswel. Taking into account wheel base and the like, can they check speed. ??

I don’t suppose your ex-cop explained exactly how they could do that. Winding you up, I suspect.
I’m not even sure how they could count vehicles. E.g. a 6 axle artic vs 3 two-axle vans/cars . Etc.

IIRC there needs to be two 'cables'* for them to do speed.

*air filled tubes, again IIRC.

Edit, here you go, capabilities straight from the manufacturers mouth https://www.metrocount.com/tube-counters

Wossname wrote: Wed Oct 22, 2025 11:26 am I don’t suppose your ex-cop explained exactly how they could do that. Winding you up, I suspect.
I’m not even sure how they could count vehicles. E.g. a 6 axle artic vs 3 two-axle vans/cars . Etc.

An artic followed by three cars would look something like ^^^_^^^________^^_____^^_____^^______

Dodgy69 wrote: Wed Oct 22, 2025 11:19 am Those black cables they put across roads. Are they just counters.? They've put a few up around here and an ex cop once told me they can check for speeding aswel. Taking into account wheel base and the like, can they check speed. ??

If they're a fixed distance apart, even a couple of inches, then yes. With a certain, limited, degree of accuracy. Front wheels go over first one and a v short time after they go over the second so eg the car is travelling at, say, 6in in 0.25sec. Vehicle is travelling at ~1.2mph.

They could get a general idea of traffic volumes and speed but, from what I've seen of these things it'll only be vv general. There are easier, more accurate ways to log vehicle speeds.

As timed distance measurers they were probably better than their predecessors, plod with a stopwatch!

They tend to be a survey tool to get an idea of vehicle numbers and average speed. Normally a precursor to lowering a speed limit or adding some detection/enforcement system.

I've installed loads of counters in Lancashire (not since 2006 though) and had many more installed for me - for every study I was doing at the time.

The tubes are set 1 metre apart and they count the number of vehicles crossing them and the speed of the vehicles. The printout that they generate put the vehicles into speed brackets so people like me could calculate the 85 percentile speed and the amount of traffic that was passing in each particular speed bracket at particular times of the day.

We'd normally leave them down for a week and a few times I put out 2 or 3 separate counters on the same stretch of road to get an idea of drivers slowing down for speed cameras or drivers accelerating away from a roundabout for example up to a National Speed Limit sign.

They provide very useful information and insights into traffic behaviour.

Ha I was wondering about these yesterday. I've always figured they are there to get an idea of the speed people are doing. But vehicles have all different wheel bases and bikes tend to be quite short. So if I go over a set at the speed limit, does it think I am speeding due to being shorter than an average car? And can a bus go over a set at twice the limit and be registered as being on the limit?

McNab wrote: Wed Oct 22, 2025 3:45 pm Ha I was wondering about these yesterday. I've always figured they are there to get an idea of the speed people are doing. But vehicles have all different wheel bases and bikes tend to be quite short. So if I go over a set at the speed limit, does it think I am speeding due to being shorter than an average car? And can a bus go over a set at twice the limit and be registered as being on the limit?

A pair of them measure the speed of each axle - the distance between them doesn't really matter, you'll get 2 readings for a typical car. (The axles are usually travelling at the same speed ). They might have difficulty separating out individual vehicles but I imagine they're looking at averages.

Individual ones will only count the number of axles crossing.

Topical around here

I still don't get the speed thing though. Lots of different vehicles with lots of different axle positions. Unless it's so clever it can identify each vehicle, I don't get it.


Oh...maybe 4 cables. They can only measure the time difference between each input.

Dodgy69 wrote: Wed Oct 22, 2025 5:09 pm I still don't get the speed thing though. Lots of different vehicles with lots of different axle positions. Unless it's so clever it can identify each vehicle, I don't get it.


Oh...maybe 4 cables. They can only measure the time difference between each input.

No. Imagine car with only one axle. It goes over the first one in the pair of cables, then the second. Time between squashing the first and second cable is measured and the (fixed) distance between the cables give you the speed of the axle. Add a second axle, provided it doesn't cross the second cable before the front axle crosses the first, you get a second reading, same as the first. So, a two-axle car gives a matching pair of speed readings.

Count Steer wrote: Wed Oct 22, 2025 5:43 pm No. Imagine car with only one axle. It goes over the first one in the pair of cables, then the second. Time between squashing the first and second cable is measured and the (fixed) distance between the cables give you the speed of the axle. Add a second axle, provided it doesn't cross the second cable before the front axle crosses the first, you get a second reading, same as the first. So, a two-axle car gives a matching pair of speed readings.

They just installed a pair here on a 50mph limit, everyone is hitting them at 70-80mph.

Skid the wheels over them. You wont take me alive copper.

Count Steer wrote: Wed Oct 22, 2025 5:43 pm
No. Imagine car with only one axle. It goes over the first one in the pair of cables, then the second. Time between squashing the first and second cable is measured and the (fixed) distance between the cables give you the speed of the axle. Add a second axle, provided it doesn't cross the second cable before the front axle crosses the first, you get a second reading, same as the first. So, a two-axle car gives a matching pair of speed readings.

Now it makes sense

McNab wrote: Thu Oct 23, 2025 8:46 am

Count Steer wrote: Wed Oct 22, 2025 5:43 pm
No. Imagine car with only one axle. It goes over the first one in the pair of cables, then the second. Time between squashing the first and second cable is measured and the (fixed) distance between the cables give you the speed of the axle. Add a second axle, provided it doesn't cross the second cable before the front axle crosses the first, you get a second reading, same as the first. So, a two-axle car gives a matching pair of speed readings.

Now it makes sense

And presumably 6 axles, in a particular sequence, identifies an artic.

the two tubes are there to be able to discriminate between the vehicles travelling in each direction, I am quite positive the speed would only be an indicative measure and not that accurate, also if it were to be used for enforcement it would have to be VCA approved which I am sure they are not

Wossname wrote: Thu Oct 23, 2025 11:05 am

McNab wrote: Thu Oct 23, 2025 8:46 am

Count Steer wrote: Wed Oct 22, 2025 5:43 pm
No. Imagine car with only one axle. It goes over the first one in the pair of cables, then the second. Time between squashing the first and second cable is measured and the (fixed) distance between the cables give you the speed of the axle. Add a second axle, provided it doesn't cross the second cable before the front axle crosses the first, you get a second reading, same as the first. So, a two-axle car gives a matching pair of speed readings.

Now it makes sense

And presumably 6 axles, in a particular sequence, identifies an artic.

There was no reason to identify vehicle types for the speed counts I carried out. The data that was important to me for most studies was the speed of the general traffic. My work was to look for accident patterns and of course, speed may well have played a prominent role in that. I would know from the accident reports if HGVs were a factor but tbh I can't remember any study I carried out where they were. The presence of a lot of HGVs can act as a traffic calming measure.

Oh, and the equipment on the road are not cables, they are rubber tubes. The end of the tubes not connected to the counter were usually sealed with a simple overhand knot and the clamps holding the tubes were held in place by thick (about 8mm iirc) nails.