Two rubber lines on road - what are they?
Discussion
Probably the wrong section for this question but does anyone know what the two rubber lines are that keep appearing on different roads on my commute to work? Are they counting quantity/density of traffic or measuring traffic speed? They always seem to be plugged in to a little grey box padlocked to some other road furniture.
Traffic measurements: http://www.reddit.com/r/explainlikeimfive/comments...
hmm so they measure speed. I thought they might. They seem to be in the new(ish) 50 limits around us. Are they checking the proles are sticking to the new limits? Is it childish that I try to go as quickly over them as possible (naturally only when safe to do so and wouldn't dream of doing it if they were in a built up area).
chrisga said:
hmm so they measure speed. I thought they might. They seem to be in the new(ish) 50 limits around us. Are they checking the proles are sticking to the new limits? Is it childish that I try to go as quickly over them as possible (naturally only when safe to do so and wouldn't dream of doing it if they were in a built up area).
Yes. If enough people are abusing the limit, the council will bring in traffic calming measures I imagine.These all seem to be appearing on open, straight, non-urban stretches of A-road that used to be NSL until a few years ago with good visibility. Hoping it might help prove that the reduction to a 50mph limit is unnecessary? Very, very few cars seem to travel at the 50 limits around us and those that too stay at 50 even when it goes in to the NSL so I assume they don't really know the speed limit anyway. Do they still review limits based on percentiles, or is that a one way thing i.e. if its lower they will lower the limit but if higher they leave it as is?
Boydie88 said:
chrisga said:
hmm so they measure speed. I thought they might. They seem to be in the new(ish) 50 limits around us. Are they checking the proles are sticking to the new limits? Is it childish that I try to go as quickly over them as possible (naturally only when safe to do so and wouldn't dream of doing it if they were in a built up area).
Yes. If enough people are abusing the limit, the council will bring in traffic calming measures I imagine.They are used more often just to count traffic, than to measure speeds. I have used these loads of times - only once was it anything to do with speed limits (and that was for "before" and "after" checks in a pick-up drop-off and taxi zone outside an airport terminal building).
Tinfoil hats back in the box lads!
Tinfoil hats back in the box lads!
They are used more often just to count traffic, than to measure speeds. I have used these loads of times - only once was it anything to do with speed limits (and that was for "before" and "after" checks in a pick-up drop-off and taxi zone outside an airport terminal building).
Tinfoil hats back in the box lads!
Tinfoil hats back in the box lads!
tvrgit said:
They are used more often just to count traffic, than to measure speeds. I have used these loads of times - only once was it anything to do with speed limits (and that was for "before" and "after" checks in a pick-up drop-off and taxi zone outside an airport terminal building).
Tinfoil hats back in the box lads!
This. Tinfoil hats back in the box lads!
And they shouldn't really be used for checking speeds - a proper manual radar survey is more accurate. They are helpful though when you want both speeds and counts.
mikeveal said:
And if the traffic is driving slower, they will reduce the limit. 85th percentile speed limit. Ye cannot, I tell ye, win.
I was wondering about this. Isn't the 85th percentile measurement only really valid on roads that don't have a defined speed limit.If you try to do this measurement on a road that has a speed limit in place then you aren't getting a true measure of the 85th percentile speed since some drivers will keep their speed artificially low because of the speed limit itself.
From that document you posted:
"The 85th percentile speed is the speed that reasonable people tend to adopt according to the road environment. The 85th percentile is called the "operating speed" and is not related to the roads posted speed limit"
I use the gym at the local University. There is a 1 mile straight road once in the grounds that has a 20mph limit. I don't think I've seen anyone go below 50mph, including buses. They've recently installed this monitoring kit.
Question: as it's private property they can't enforce any speed limits legally, so what would the point be in changing the speed limit as a result? Maybe it's used to monitor car volume as parking is scarce?
Question: as it's private property they can't enforce any speed limits legally, so what would the point be in changing the speed limit as a result? Maybe it's used to monitor car volume as parking is scarce?
Moonhawk said:
mikeveal said:
And if the traffic is driving slower, they will reduce the limit. 85th percentile speed limit. Ye cannot, I tell ye, win.
I was wondering about this. Isn't the 85th percentile measurement only really valid on roads that don't have a defined speed limit.If you try to do this measurement on a road that has a speed limit in place then you aren't getting a true measure of the 85th percentile speed since some drivers will keep their speed artificially low because of the speed limit itself.
From that document you posted:
"The 85th percentile speed is the speed that reasonable people tend to adopt according to the road environment. The 85th percentile is called the "operating speed" and is not related to the roads posted speed limit"
tvrgit said:
They are used more often just to count traffic, than to measure speeds. I have used these loads of times - only once was it anything to do with speed limits (and that was for "before" and "after" checks in a pick-up drop-off and taxi zone outside an airport terminal building).
Tinfoil hats back in the box lads!
Single Rubber Lines count traffic though, why would they need 2 rubber lines.Tinfoil hats back in the box lads!
Centurion07 said:
What roads are those then?
I wasn't referring to actual roads - merely pointing out that the 85th percentile is supposed to be a measure of what a "reasonable person" considered to be an appropriate speed in the absence of a defined limit (see the text I quoted).The presence of a speed limit will give a distorted view of the 85th percentile as some drivers will abide by the speed limit even if they would consider it reasonable to travel faster in the absence of it.
Could this be the reason we have seen wholesale reductions in limits. The wrong application of the 85th percentile?
Edited by Moonhawk on Tuesday 28th April 16:37
Foliage said:
Single Rubber Lines count traffic though, why would they need 2 rubber lines.
Yep - I always thought the single ones were to count traffic. The double ones with a defined spacing were to gather average speed data.Most of the places I have seen them employed appear to have been just before or just after a change to the speed limit on a particular road.
Looking at the manufacturer's websites for these type of devices (pneumatic traffic counters) - they indicate that they can measure speed.
http://metrocount.com/shop/traffic-counters/26-mc5...
http://www.vehiclecounts.com/
Foliage said:
Single Rubber Lines count traffic though, why would they need 2 rubber lines.
Single rubber lines can only count AXLES. Two tubes mean you know the DIRECTION and also mean you can count vehicles (that's where the "speed" comes in - it measures speeds so that it can tell that all the axles are on the same vehicle - so it can normally also "classify" counts into vehicle types depending on the weight (force of the "puff" of air) plus number of axles plus the distance those axles are apart (interval between axles at the same speed). I don't know how they do that, but I do know that they do!
I have always used twin tube counters - but as I said earlier, only once to actually measure speeds as the end result. As Swerving Mervin said, they way they measure speeds, and store them in "bins" rather than each individual speed, isn't really suitable, in my mind, for calculating design speeds - radar hand guns are better because you are only supposed to measure the "free-flow" speed, not 20 vehicles following a tractor in a convoy, for example. But then you get posts like "I saw some community speed watch b
d recording speeds, and nearly got out and started a rammy" type posts...Edited by tvrgit on Tuesday 28th April 17:03
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