Safe Speed Forums

It's a constant and vital Safe Speed theme that 'speed' isn't a simple thing to measure and specify usefully. It's all to easy to think that 'speed is speed, and that's the end of it.' But of course we all know that's got us into a horrible mess.

Here's what I wrote in 2004



Since then I've been terming 'appropriate speed' as 'relative' and 'numerical speed' as 'absolute'. This terminology is useful to scientists and engineers, but seems to mean little to journalists or politicians.

I've just realised that we could also use the terms 'qualititative' and 'quantitative' in a similar way. But it's still awfully technical.

Get your thinking caps on chaps, and let's nail this vital point in a way that's obvious to everyone (or at least the smarter 50% of the population).

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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

but in the context of a vehicle..... the worst case relative speed is in relation to a stationary pedestrian..... or object.... which is the same as numerical.

perhaps appropriate speed is subjective, since numerical speed is clearly objective (i.e. can be absolutely measured/quantified).

(neither of which i confess are any better for journos)

OK, I'll have a go..........

Your first definition should stick with appropriate. Everything we do when driving/riding has to be appropriate for the conditions. Where we look, where we position, what gear we're in and what speed we are going must all be appropriate.

The second is more tricky but I'm tempted towards reference.

I look at my speedo for reference - and that's the only reason I look at it. Depending on the road conditions, my perception of my actual speed can vary. A quick look down gives me a reference point.

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It's tricky doing nothing - you never know when you're finished

No! No!

A pedestrian displaced sideways by 100 feet could safely be passed at 150mph.

A pedestrian displaced sideways by only six inches would force us to slow to under 5mph.

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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

The thing is that speed isn't important - no matter how you try to dress it up as "appropriate", "qualitative" , etc. It is space and time that matter.

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Will

Not sure how you can make more simple that you have.

Appropriate speed is.....appropriate speed.

I have difficulty with the term 'speeding' what does it mean?

I'm with Willcove on this. It is all about space and time. If you have the space and time you can be doing a huge numerical speed. Without knowing the space and time you cannot judge whether the speed is appropriate, you can only know its numerical value.

5mph with no space is catastrophic, ditto 5 mph with no time. It's too much of a metaphysical argument for the plebs to grasp as they are only interested in what their speedo says. Even the 50% if those that are bright wouldn't understand the significance, at least not without the right kind of prodding and the understanding you have to reference speed in terms of the context of whatever situation you are doing that speed in.

hmmm ok then... relative velocity?

Yet the vast majority of 'the plebs' are capable of driving reasonably safely. To do that they MUST be making the safety judgements. Can't we 'connect' to what they know?

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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

Almost always these days it means 'exceeding the speed limit', and I only ever use it with that definition.

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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

I'm by no means sure that I agree with you on that. It seems to me that speed and space need to be 'in balance'. They are highly interdependent, but as a driver I think I mostly make space by adjusting speed.

You might be suggesting that speed is only an agent used to make space, which tends to fit with my practice; but that still doesn't feel right.

But for risk control, I think I use something very much like Steve Haley's model: http://www.safespeed.org.uk/sss.html

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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

I try to avoid the term 'speeding' but I reckon that when the brake lot refer to 'speeding' drivers I suspect they really mean travelling at a dangerous speed.....or an inappropriate speed. They've just not been educated to disconnnect that from adherence to the limit.

Maybe the gulf isn't as wide as we think?

Speed isn't a primary factor of safety. If it were, you'd keep safe by setting a particular speed and then adjusting other factors to maintain that speed. However, that doesn't happen - speed is the factor most commonly adjusted to maintain other things.

Now driving with COAST requires you to concentrate on your driving, observe what's going on around you, anticipate possible hazards and give yourself enough space and time to deal with hazards before they become problems. If you do that, you will drive safely. Note that "speed" doesn't appear anywhere in that list - and that's because if you drive with COAST you will automatically choose a safe speed at all times. IOW, speed is a dependent factor - and thus must be secondary to the determinant factors.

In my earlier post, I wrote that space and time are important - and that's because they are often interdependent. In many situations, you can trade time for space and vice versa. For example, when passing a row of parked cars on your left, you can give yourself both by moving further to the right. If you can't move over, then you have to buy yourself extra time by slowing down.

I suspect that the situations you're thinking of when speed and space need to be in balance is where you're adjusting both to give yourself enough time. In those circumstances, neither speed nor space are primary factors.

Whether time or space is more important depends on the circumstances. For example, with high hazard density, the most important factor is the time required to properly scan your surroundings. On a twisting, single-track country road, the most important factor is the space required for you and an oncoming vehicle to stop.

HTH,

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Will

Which in their case means "anything over 4mph"!

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"Politicians are the same the world over... We build bridges where there aren't any rivers." - Nikita Kruschev

Maybe but it's their perception of an appropriate speed.....is there a glimmer of hope?

For sake of argument, suppose we're driving with all our risks well controlled. If we spuriously accelerate hard then quite quickly we'll be experiencing substantially elevated danger due to speed.

Normally we use something akin to the safe speed rule to keep speed and space in balance.

Now the bit I've emboldened seems to be at the centre of this. You are refering to 'numerical speed'. Clearly that's no help - I agree. However, if instead we talk in terms of the appropriateness of a speed then surely it's a primary safety factor?

Or perhaps this helps - speed is an OUTPUT of the risk assessment process that underpins safe driving.

A few disconnected points, I know, but I'm trying to connect with the difference between the view you have expressed and my views.

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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

I'd say that we elevated the danger because we ignored the primary factors.


Actually, I use the safe speed rule only where it's on the "critical path". How fast I'm going (subject to remaining legal) often depends on how far I can see and how quickly I can complete my scan. I don't feel safe unless I can drive at least ten seconds ahead of myself (i.e. scan up to at least where I'll be in ten seconds). The Safe Speed rule(tm?) applies when conditions deny me that scanning range and/or I spot a hazard that reduces my "cleared safe area" (the region from which I've discounted all hazards). For example, on approach to a junction I make sure I can stop before that junction until I'm satisfied that no conflicting road users are going to pull out of or turn into it.


Yep, I will agree with that. Speed and road position are the outputs of the process and it is by manipulating those factors that we give ourselves enough time to spot and deal with hazards, and enough space to keep safe.

However, concentrating on the outputs of the risk assessment process is like putting the cart before the horse. IMO, we need to understand the inputs to that process and why they are important. For example, the safe speed rule doesn't mention speed and it makes perfect sense (Always ensure that you are able to stop comfortably on your own side of the road within the distance you know is clear and will remain clear). If we don't understand the inputs (the need to have enough time to properly observe and anticipate, the need to have enough space to take avoiding action before hazards become problems, etc.) the outputs can seem as arbitrary as speed limits themselves.

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Will

That's close to what I was trying to express here and here

Yeah. NOW I understand what you mean. We agree, I think, except for the terms.

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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

I'm going off COAST. Risk management and responsibility are only weakly present.

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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