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FLASHED BY SPEED CAMERA - will i be fined?
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coulsontom
That wasn't quite the point I was trying to make. Of course you shouldn't crawl down the motorway. But speed limits are set with the conditions of the road in mind. There could be residential areas nearby and someone could step out into the road and if you are sticking to the limit of 40 rather than 48 then surely the person has a better chance of living or you have a better chance of avoiding the collision.
I don't know about you but I haven't seen many people walk into the outside lane of the motorway?
I don't know about you but I haven't seen many people walk into the outside lane of the motorway?
Theres a little road near Honiton that is mightily steep - comes of a road with a limit of 50...its NSL - your car would break if you tried to do NSL on that - so it might be set to the conditions of the road - but they dont always do its sensibly...
and thats why I said someone/thing - someone did get killed trying to cross the motorway quite recently - they were going back to get their handbag theyd left in their broken down car...
I don't know who neg repped me for saying that GPS speed was accurate in this thread, but everything I said about GPS was correct!
GPS receivers display speed and calculate the speed using algorithms in the Kalman filter. Most receivers compute speed by a combination of movement per unit time and computing the Doppler shift in the pseudo range signals from the satellites. The speed is smoothed and not instantaneous speed.
From the NAVSTAR GPS User Equipment Introduction document Section 3.7:
GPS receivers typically calculate velocity by measuring the frequency shift (Doppler shift) of the GPS D-band carrier(s). Velocity accuracy can be scenario dependent, (multipath, obstructed sky view from the dash of a car, mountains, city canyons, bad DOP) but 0.2 m/sec per axis (95%) is achievable for PPS and SPS velocity accuracy is the same as PPS when SA is off.
Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on.
"For a graduate you give pretty crappy advice." So what was so crappy about it then?
Marcus
GPS receivers display speed and calculate the speed using algorithms in the Kalman filter. Most receivers compute speed by a combination of movement per unit time and computing the Doppler shift in the pseudo range signals from the satellites. The speed is smoothed and not instantaneous speed.
From the NAVSTAR GPS User Equipment Introduction document Section 3.7:
GPS receivers typically calculate velocity by measuring the frequency shift (Doppler shift) of the GPS D-band carrier(s). Velocity accuracy can be scenario dependent, (multipath, obstructed sky view from the dash of a car, mountains, city canyons, bad DOP) but 0.2 m/sec per axis (95%) is achievable for PPS and SPS velocity accuracy is the same as PPS when SA is off.
Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on.
"For a graduate you give pretty crappy advice." So what was so crappy about it then?
Marcus
Wasn't me either. I do agree that GPS is potentially very accurate, my experience has tended to show it is not always that accurate in practice. Plenty of reasons for that, such as the ones you give, but my take on it is that I would not trust a GPS to give me more accuracy to more than a couple of miles an hour without some external reference on its accuracy. As I mentioned, one of my GPS units gave a reading of 14mph for a few seconds whilst being on a windowsill, so it's perfectly possible for them to be off. As speed increases I think the error will get smaller.
I did hear a while back of a guy sailing a yacht, and you're always taught not to rely solely on GPS, and this guy plotted a position which was half a mile from the GPS position. He assumed the GPS was right and hit the rocks!
I did hear a while back of a guy sailing a yacht, and you're always taught not to rely solely on GPS, and this guy plotted a position which was half a mile from the GPS position. He assumed the GPS was right and hit the rocks!
Reply 45
tomoli
Why on earth did they breakdown, then cross the motorway?
exactly
CurlyBen
Wasn't me either. I do agree that GPS is potentially very accurate, my experience has tended to show it is not always that accurate in practice. Plenty of reasons for that, such as the ones you give, but my take on it is that I would not trust a GPS to give me more accuracy to more than a couple of miles an hour without some external reference on its accuracy. As I mentioned, one of my GPS units gave a reading of 14mph for a few seconds whilst being on a windowsill, so it's perfectly possible for them to be off. As speed increases I think the error will get smaller.
I did hear a while back of a guy sailing a yacht, and you're always taught not to rely solely on GPS, and this guy plotted a position which was half a mile from the GPS position. He assumed the GPS was right and hit the rocks!
I did hear a while back of a guy sailing a yacht, and you're always taught not to rely solely on GPS, and this guy plotted a position which was half a mile from the GPS position. He assumed the GPS was right and hit the rocks!
Doh!
Charts and depth readers! Cannot beat them
gbduo
Oh bugger! That would sting a bit, especially if those cables were live!
Not so, even if there was a high voltage line touching the cab he would be perfectly safe if he stayed in the tractor - assuming no crushing - as the body would act like a Faraday Cage and the rubber wheels would insulate the vehicle from the ground.
I remember when I was younger, a digger driver brought down some power lines near me. The poor driver was electrocuted as he got out of his vehicle as they only made an earth connection when he touched the ground.
Marcus
marcusfox
Not so, even if there was a high voltage line touching the cab he would be perfectly safe if he stayed in the tractor - assuming no crushing - as the body would act like a Faraday Cage and the rubber wheels would insulate the vehicle from the ground.
I remember when I was younger, a digger driver brought down some power lines near me. The poor driver was electrocuted as he got out of his vehicle as they only made an earth connection when he touched the ground.
Marcus
I remember when I was younger, a digger driver brought down some power lines near me. The poor driver was electrocuted as he got out of his vehicle as they only made an earth connection when he touched the ground.
Marcus
They showed that on Top Gear a while ago with Hammond in a Golf! Not sure it's an experience I'd like to go through though..
I'm probably wrong, but I think someone once told me that there's some kind of automatic cut off system if a pylon is felled for whatever reason? One of my friends was telling me about her uncle, who used to repair pylons, but was on one when the power was switched on prematurely and got very badly burnt. Apparently the guy he was with had to undo the buckle on his harness and burnt his whole arm doing that. I'm not entirely sure what he was earthed to but it doesn't sound like fun!
CurlyBen
They showed that on Top Gear a while ago with Hammond in a Golf! Not sure it's an experience I'd like to go through though..
I'm probably wrong, but I think someone once told me that there's some kind of automatic cut off system if a pylon is felled for whatever reason? One of my friends was telling me about her uncle, who used to repair pylons, but was on one when the power was switched on prematurely and got very badly burnt. Apparently the guy he was with had to undo the buckle on his harness and burnt his whole arm doing that. I'm not entirely sure what he was earthed to but it doesn't sound like fun!
I'm probably wrong, but I think someone once told me that there's some kind of automatic cut off system if a pylon is felled for whatever reason? One of my friends was telling me about her uncle, who used to repair pylons, but was on one when the power was switched on prematurely and got very badly burnt. Apparently the guy he was with had to undo the buckle on his harness and burnt his whole arm doing that. I'm not entirely sure what he was earthed to but it doesn't sound like fun!
Usually they work on them live where possible, but without being earthed (obviously!)
Marcus
tomoli
Why on earth did they breakdown, then cross the motorway?
I don't know why they broke down, but from what I remember from the article they broke down in an outside lane, made it safely to the hard shoulder, realised they had left their handbag in their car, and went back for it...
May as well use this thread ... Was just driving home on the dual carriageway doing at least 80 and spotted a police car (it was a people carrier thing, not a normal traffic cop car) in the hard shoulder. I slowed down to 70 as I was passing it.
Do you think it might have been doing speed checks? And if so can they do it out the back window or does it have to be out the front (as you're driving away from them)?
Do you think it might have been doing speed checks? And if so can they do it out the back window or does it have to be out the front (as you're driving away from them)?
Nah wasn't being stupid, from what I remember most the other cars were doing the same.
If they are doing speed checks are the side of the road do they have to pull you over to fine you or can they just record your plate and send you a fine in the post?
And I've seen that ANPR thing on "Traffic Cops" - clever stuff.
If they are doing speed checks are the side of the road do they have to pull you over to fine you or can they just record your plate and send you a fine in the post?
And I've seen that ANPR thing on "Traffic Cops" - clever stuff.
Related discussions
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What happens if you accidentally drive your car with no road tax or motLast reply 4 months ago
Is it a driving test fail to almost pull out on somebody but rectify this and brake?
