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 Post subject: Time to React
PostPosted: Sat Apr 10, 2004 09:11 
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This topic relates to the Safe Speed page: "Time to React".

http://www.safespeed.org.uk/timetoreact.html

The Safe Speed page explores the issue of "time to react" and lists the real world factors that contribute to it.

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PostPosted: Mon Jun 21, 2004 14:06 
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Hi

Interesting page, with quite a detailed look at the problem.

One line catched my attention:

"They fail to recognise the huge value of the "closed loop" hazard speed feedback system that drivers use accurately and instinctively. "

I don't think this notion of "closed loop" feedback has been explained elsewhere on your site. I think I understand what it is, but that would be worth a detailed explanation, if you're able to put it into words correctly (something you've done very well for other difficult topics in this site 8-) ).

I know at least a French book on human factors which talks in detail about this feedback notion, but in a general way, ie oriented towards all risk systems (not particularly driving and speed).

Btw since I'm new here, I have to congratulate you for the website, probably the best I have seen about road safety.

(Sorry for my English mistakes, as this is not my native language).

Best regards.


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PostPosted: Mon Jun 21, 2004 14:57 
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gaspard wrote:
"They fail to recognise the huge value of the "closed loop" hazard speed feedback system that drivers use accurately and instinctively."

I don't think this notion of "closed loop" feedback has been explained elsewhere on your site. I think I understand what it is, but that would be worth a detailed explanation, if you're able to put it into words correctly (something you've done very well for other difficult topics in this site 8-) ).


Yes, you're right. This is a very important concept and so far I haven't done it justice. I'll have a go at it right now, and probably add something more to the page later.

Firstly we use the expression "closed loop" for any control system where the effect feeds back to a cause. An example would be heating controlled by a thermostat - when the room is warm enough the thermostat detects this and shuts off the heating. If the room is too cold, the thermostat detects this and turns on the heating.

The alternative is open loop, where (in our example) a heater blasts away delivering heat irrespective of the temperature in the room. You could vary the power of the heater and still arrive at a steady temperature, but if the heat loss from the room increased (for example on a cold day) the temperature would drop.

The closed loop speed / hazard system works like this: A driver sees a hazard ahead that causes him to reduce speed. As he gets closer and learns more about the hazard, he might reduce speed still more or he might learn that he is travelling sufficiently slowly and maintain his speed. Or (third alternative) the hazard might clear and he might accelerate again.

Imagine the process of drawing up behind stationary traffic. If the traffic starts to move off, we quickly adjust and accelerate to maintain a suitable gap.

The feedback process is especially noticable on the approach to bends. We control our speed in accordance with the behaviour of the vanishing point - if the vanishing point is moving towards us we reduce speed. If it is moving away we increase speed. If it stays the same distance (as in mid curve) we maintain a constant speed.

By varying speed we control the risk we are exposed to. An experienced driver is likely to be very skilled at estimating risk and adjusting speed.

gaspard wrote:
I know at least a French book on human factors which talks in detail about this feedback notion, but in a general way, ie oriented towards all risk systems (not particularly driving and speed).

Btw since I'm new here, I have to congratulate you for the website, probably the best I have seen about road safety.

(Sorry for my English mistakes, as this is not my native language).


Thank you for your kind comments. Your English is excellent and requires no apology.

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Our scrap speed cameras petition got over 28,000 sigs
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PostPosted: Tue Mar 13, 2007 13:50 
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Hi,

Let's say I have a friend who's been driving "enthusiastically" for over twenty two years, in vehicles ranging from 1.3 Escort vans to 130hp 7ton trucks, from 44hp Mini's to 235hp Subarus, all with an total disregard for speed limits but with a serious regard to travelling at a safe speed, remaining alert and ensuring the safety of self, passengers and other road occupants and bystanders alike. He has expired points for one (illegal) prosecution for speeding but no accidents or other blemishes to his name. He regularly throws his vehicle around a bit, occasionally deliberately slides it around in snowy, wet or muddy conditions, and while he doesn't know what 145mph feels like, he's been close as he felt safe on deserted bridge free tarmac. He rides his motorcycle much as he drives too, but confesses to having low sided on a roundabout DERV slop twenty years ago - a lesson learned?

Well, if the average driver has an accident every 7 years, what percentile of the population is my friend in at less than one in 22 years?

Is there a correlation between accident rate (per year, per 10,000 mile or whatever) and such enthusiastic or hobbyist driving? Or a correlation between low accident rates and a measurable level of interest in the process of safe driving? Has there been any research here?

As our protective instincts only really kick in when we percieve a risk, is it even possible that there's a correlation between relative safety and the state of mental alertness that can accompany somewhat brisk driving i.e. beyond that permitted by many of our (often recently ridiculously lowered) potentially mind numbing speed limits?

Cheers, BB.


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