Safe Speed Forums

I skipped from page 5 to about page 22 because the thread was becoming ridiculous and then to here because so much of what I am reading is just CRAP.

I have a GPS unit in my car which gives a fairly constant and accurate speed reading. Recently I actually drove for about 1 kilometre spending about 80% of my time watching the unit to see if I could maintain a consistent speed. (Very little traffic, dry and flat road)

To my horror my speed varied up and down by about 3-4kph (a total variation of between 6 and 8kph) no matter how hard I tried to maintain the exact speed. My horror is due to the fact that in Victoria, Australia, the tolerance is 3kph so we can be booked for doing 104kph in a 100kph zone. I should note that the speedo does not and cannot show this level of accuracy, but the police claim their equipment can.

If I cannot maintain my speed on a flat road to within 3kph while spending almost all of my time watching my speed what hope have I got of maintaining my speed to the degree of accuracy required here without looking at my speedo constantly?

Yes, I do choose to speed sometimes, but given how hard it is to maintain a constant speed I would imagine that I am speeding much more often than I thought without having any idea I am doing so, and I have over 30 years of driving experience.

I am so sick of cameras I am planning to emigrate from Australia to Fiji when I retire where, although the national limit is 80kph, there are no cameras and only occasional police, so I can drive at an appropriate speed for the conditions and devote the vast majority of my concentration on what is ahead of me rather than watching my speedo to make sure I am not booked for accidentally speeding.

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Ross

Yes I'm a hoon, but only on the track!!!!

Long time no see, Ross.

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Hi Ross! back Merry Christmas mate!



Ah... basingbonce and a withches cat - but rather think a certain got the witcheescat's tongue as it's not been back since!




How - their equipment is neither more nor less accurate than ours. Whatever happened to professional judgement? and commons sense?

I know - GPS shows how speed fluctuates on any one journey and even if car was comptuter controlled - you'd still have the variance as you descirbe because of road surfaces

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Approach love and cooking with reckless abandon - but driving with a smile and a COAST calm mind.

Actually, GPS isn't particularily accurate or consistant for measuring speed. They work by working out your position, accurate to about 25m, and you can get a reading once a second. However, each reading will give you a random position within a 25m diameter circle, completely unrelated to the error in previous readings. If one reading puts you at (for example) the position of the circle furthest behind the car, and the next at the front of the circle, your speed will be calculated as if you travelled 25m further in that time than you actually did.

Of course, this is an overly simplified view of the situation, your GPS unit will be doing some averaging to avoid large jumps in speed, but it could easily show that 3-4kmh drift with you actually going at exactly the same speed.

Contrast that with the speedo in your car. At 100kmh, it could be out by up to about 10kmh in either direction. But it will stay that same proportion out, the speedo won't drift (beyond a small neglibable amount).

GPS speed is more accurate, but less consistant. Mechanical speedo is less accurate but with a consistant error factor, and thus more suitable for checking the consistancy of your own speed perception.

Actually that's not correct. GPS systems usually or always have a secondary system for measuring speed based on doppler effect. A commonly quoted maximum error is 0.1mph.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Where did you hear about that? I researched quite heavily into GPS a few years ago, and while there are a few clever algortithms to improve speed accuracy, it's nowhere near that level.

I read something here about it:
http://gpsinformation.net/main/gpsspeed.htm

"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."

If I may, I would like to come back to your original post, Safespeed.



I agree with this reasoning. There is that theory on "risk homeostasis" that says just that.
But I think it should be clear these subsonscious risk assessments are not objective science, they are estimations one makes based on all info and circumstances gathered instantaneously.
I hope I make myself clear: it is the risk as it is perceived, not as it really is, one reacts upon. As a result one can make the wrong decision, choose the wrong speed. I believe all traffic incidents are caused by a mismatch between real and perceived risk.

I think the clue on how to improve road safety is to bring real (objective) risk and perceived (subjective) risk in line. So risk reduction itself is therefore not the primary goal, but the chance the risk factors remain unnoticed is.

(I skipped most of the ongoing discussion, so I apologize if this does not contribute to the discussion)

Absolutely.

SO - how to deal with a situation where actual risk consistently outweighs perceived risk. Reduce the speed limit? No - not unless it is too high for the general area. Put up a camera to ensure that, chavs apart, drivers look down at the speedo exacerbating the risk imbalance? No.

Put up chevrons if it is a deceptive bend? Yes. This works demonstrably.

Put "SLOW" in big letters on the carriagway? Yes. This has saved countless accidents.

It may prove usefull to do just that. A speed limit well directed at that specific location or situation is a signal to drivers there is some critical situation ahead (SLOW painted on the carriageway may have the same result). Clearly general speed limits have little value in that respect.
It is sort of the German way of working with speed limits.

Do signs and speed limits add or detract from your perception of risk?

First reaction must be they 'add' but isn't there also a distraction element that might 'detract'. Councils seem to throw signs up at every opportunity and speed limits seem to have extended well beyond the potential hazard.

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It would appear that very few "planners" have read the story of "The Boy Who Cried 'Wolf'".

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Oh I'm sure she's much better than that - according to what she tells us - frequently!!

Happy New Year everyone, drive safely,
Dave.

Hello! What a thread, very entertaining!!

I would like to answer the original question, why do i speed? But first a little background to introduce myself...

I am a very late driver having only passed my test in Nov '04 at the age of 32, i have been driving company pool cars for the last 13 months and only last week did i buy my first car (A new Golf). The day after i passed my test i drove to London and back on my own (i live in the North West) and my learning curve has carried on from there (steep, have done probably 25,000 miles) I very soon discovered i exceed the speed limit on the motorway and roads that i feel safe speeding in and yet i have never had a crash or even had to brake 'in anger'. I drive at a speed i feel 100% confident that i have control, if i start to feel that i am not 100% in control i will slow down until i do. I think i am a very safe driver and NEVER speed in a 30 or 40 zone and will only speed on a NSL road if it is dry, clear and straight. i have already took my new car down to Cornwall and back for a jaunt and feel extremely safe doing 90mph when the conditions suit.

So why do i speed?

1 - Why should i take 3 hours to do a journey if i can do the same journey in 2 1/2 hours and still be safe?

2 - Fun, sorry to say this but i really enjoy driving and sometimes it is more fun to drive a bit faster on fun roads. I get an adrenalin rush from overtaking on A roads (But i repeat, i am not a stupid driver, i only overtake when i am sure that i can do so safely).

3 - My car is fast and has great acceleration, it is hard not to speed sometimes, i can try to keep to 40 through roadworks on the M5 but it is not easy, and besides if i spent half my time staring at the speedo i might not see the car brake in front of me.


But while i do speed i am still a great fan of speed limits, we all may agree we do not need them to drive safely but unfortunatly there are a lot of idiots on the roads who do need them (i see them everyday). It is a fact that we need general rules to protect us from the stupid. example, i do not need the gun laws to tell me i cannot shoot my wife so therefore i do not need to pay attention to them. But that does not mean for a second that i think the gun laws are stupid and should not be adhered, after all what then would stop any young idiot to shoot my wife themselves?

Anyway, cheers Murph

Why do we speed?

It's obvious. Ignoring the younger driver or those impaired through drink or drugs, people speed, to get there faster. We have a finite life-span and an awful lot of stuff to cram into those 70 odd years. Time spent getting home to our children is wasted time. Time spent in our cars and not at our destination is, for the most part, wasted. So.. we evaluate the risk, take into consideration the perfomance of our car/bike, the likelyhood of accident and prosecution and off we go!

What then when we come across someone who does not want to get anywhere quickly, but is also too lazy or inconsiderate to allow us to get past? We get frustrated and angry our precious minutes of life being squandered. We fume and rage and, is provoked beyond reason, take extra risks to get past the annoyance.

If any of what I say is remotely true to life, then police time would be better served by employing traffic police to seek out, stop and presecute those drivers who promote frustration by willfully driving too slow and not allowing traffic to periodically pass them by. I believe that it's called Driving without due care and attention!!!