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Not correct, we use higher traveling speed, where we have improved hazard perception, hence better reaction time.

Reaction time determines how much speed is reduced.

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Steve

Do you know what the word "potential" means?

If you are travelling at 10 mph, the potential maximum impact speed will be 10 mph.

If you are travelling at 40 mph, the potential maximum impact speed will be 40 mph.

I would have thought the above fell into the category of the "bleeding obvious".

Obviously driver reaction will be a major factor in determining the actual impact speed - but you can't have an impact speed of 30 mph if you're only travelling at 20 mph to start with.

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"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

Very, very steep hill?

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Make everything as simple as possible, but not simpler - Einstein

Very, very quick car in a low gear and you hit the throttle instead of the brake?

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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

You are lacking the available POTENTIAL observation, that plays one of the most significant factors.

The factors that decide what the impact speed will be:

1, How much the driver was concentrating

2, The distance available between the other vehicle and there own, when the error was made.

3, Most important, adn has the largest effect on our speed reduction. How good the visibility was, to see the hazard, ie, rain, fog, built up area, houses & vegetation blocking view.

4, How effective the braking was

5,The initial traveling speed, which is cancelled out by 1, 2, 3 & 4. Rendering the initial traveling speed irrelevant.

The more the area is built up, the lower the speed limit. The less hazard perception we have. Thus we are more likely to have higher impact speeds, in a lower speed limit area.

It is rather very clear, if you take it apart and analyse it

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Steve

Well, you can, as the others have posted, but unlikely.

However a 30 mph limit, is more likely to have a 30 mph impact.

Rather than a:

40 mph limit, impacting a 40 mph, as a 40 mph limit offers better observation to the driver.

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Steve

This is just argumentative. Obviously the pre-impact free travelling speed (for all practical purposes) defines the maximum impact speed.

Your conclusion (emphasised above) is palpable false anyway. To illustrate: take a set of traffic lights in a 30mph limit. Vehicle A jumps a red light; crossing vehicle B, travelling at the posted limit, has no time to brake or take avoiding action; impact speed 30mph. Now take a set of traffic lights in a 70mph limit. Vehicle A jumps a red light; crossing vehicle B, travelling at the posted limit, has no time to brake or take avoiding action; impact speed 70mph.

If the two junctions are identical, as you imply, then how come the one has a 30mph limit and the other a 70mph limit? The speed limit cannot be set correctly in both instances, perhaps neither. If the speed limits are correctly set, then the junctions must be quite different in the respect that you have a greater chance of avoiding a car jumping the lights at the 70mph junction than you do at the 30mph junction - either that or the chances of someone jumping the lights at the 70mph junction are far less.
So, assuming the limits are correctly set, you probably have - on average - more time to react at the 70mph junction, which in turn tends to keep the impact speed down.

Regards
Peter

Nothing argumentative in my post, in any way

Hazard perception plays a much larger role, than traveling speed.

A built up area confines our vision, if someone pulls out of a turning in a town centre, whilst traveling at 30 mph, we are less likely to of seen the vehicle approaching the junction.

Now look at your typical 70 nsl junction, which is open, and you have additional lanes to move into to allow traffic merging from junctions.

We have increased speed limits for this reason, increased visibility. Which allows us more time to react to hazards.

The less vision, the lower the speed limit.

The less speed limit, the lower reaction time, the more likely we are to impact at our traveling speed.

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Steve

The junctions could be identical or not - it really doesn't matter. They could be traffic light controlled or not - it really doesn't matter. All that's required is for a car to cross/jump the lights at the crucial moment (or during a crucial window of time).

The only point of the illustration is to show that the assertion is absurd.

I was just trying to point out that one cannot assume that speeds change without anything else changing.
If the two junctions were similar, with similar risks attached, how come the speeds varied so widely?
Why don't jet planes reduce their speed to 30mph when they're flying over urban areas? Because the conditions are completely different.

It is just possible that drivers in higher impact speed crashes have, on average, lost proportionately more speed through braking than drivers in lower impact speed crashes although, as you have produced no evidence to support the assertion, I suspect you're guessing.

In any event, that is very different to

That's a fairy tale analogy worthy of basingwerk. Look, we don't assist our cause by employing specious argumentation and extravagant claims (even if the other side does). We do have a chance of winning over opponents with carefully constructed arguments and sound logic.

Cannot argue with the hazard perception comment (COA applies - and the ST is how you deal with it.




One hopes that that relaxed concentration will have Observed the junction and Anticipated that a vehicle may pull out in front of you. You have noted it and will be forming your Driving Plan (or ST of COAST) accordingly - the routine glance in the mirror, the feathering of the brakes - and concerns of "safety, legality and consideration" You would be gathering information, need for a signal. position, adjusting your speed and selecting the correct gear.

Thus you should probably be automatically driving just below the speed lmit in any case as the "safest speed" And on course when you slow down and stop for those traffic lights - you remember to check for the two wheelied person puffing and panting his high-viz way up to the lights on your inside! Very important if you wish to turn left at this point!



But you have to allow time to see the slip road, anticipate a car may be joining - and at this point you need to be sure you have sufficient time to do all the above information gathering to be able to move into lane without causing inconvenience to another. Sure - you have the experience to do this "on auto" - but are you sure the other guy is as experienced as you are? (to play devil's advocate a bit! )


Takes about 0.7 seconds for average brain to register hazard and react regardless of speed limit - and in urban areas- lot more things to take in - which means that 30 mph is a limit and not a target. You drive at a much lower speed if the condition dictates this is appropriate. Applies just as much to faster roads as well!

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This is the absolute crux of every speed/road safety debate.

My observations and discusssions suggest to me that in a significant percentage of (compliant) drivers there is a concentration dividend gained by active speed limit compliance. I believe that the way the stats are progressing year on year adds strength to that view, especially the fatality reduction in the vulnerable road user goups, and the continued reduction in serious injuries despite fatalities not falling.

I believe that this specific camera role will eventually be responsible for a fatality reduction of 200-250 per year, (guess).

However the use of cameras as the forefront of road safety tactics at the expense of other tried and tested methods is costing us overall in lives per year. The unpopularity of cameras also has a detrimental impact.

I think our work is to try to achieve the most productive balance.

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Fixed ideas are like cramp, for instance in the foot, yet the best remedy is to step on them.

Ian

Ian, I believe that is impossible. If a benefit of concentration increase or speed reduction accrues to VRUs, then those same benefit factors MUST also apply to other groups.

Putting it another way, neither changes in speed nor changes in concentration can affect ONE road user groups without ALSO affecting others.

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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'll come back to this discussion soon Paul, unfortunately my beloved one is putting a serious lot of pressure on me to get on with DIY.

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Fixed ideas are like cramp, for instance in the foot, yet the best remedy is to step on them.

Ian

Ahh, so that's why they call it a "cop out"!

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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

No guesswork, the shear number of minor accidents on M/ways & dual c/ways that occur every day. These are minor impacts, although the traveling speed is 70 mph.

M/ways & 70 nsl, supply the most amount of hazard perception and hence allowing for the largest amount of speed reduction.

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Steve

But that's my whole point.
You made the error of assuming that conditions would be identical in both cases.
TRL made the same 'error' (deliberate?) in TRL421, when they attempted to compare accident rates on 'similar' roads but where average speed were different. As has been pointed out here and elsewhere, if the roads really are similar, then why do people do different speeds along them?