Safe Speed Forums

Worth understanding that the view regarding speed limits is not restricted to safespeed it is one shared by the institute of advanced motorists who have repeatedly called on the government to set appropriate and sensible speed limits that:

1. will have the respect of the majority of road users
2. Actually represent the maximum safe speed for the road
3. are consistent with similar roads and 'feel' right.
4. exclude social engineering and traffic volume management criteria

In reality we now have many dual carriage way high quality roads with 30 and 40 mph speed limits and muddy side tracks with 60 mph limits.

in fact on my commute to work there a high grade motorway class dual carriage way with a 50 limit that joins a similar dual carriageway 40mph that joins a residential single lane road with a 60 limit - clearly inconsistent speed limits.

I disagree with all your points bar #3.

#1 - The vast majorit of current speed limits are reasonable. They are routinely ignored.

#2 - There is no such value, a road is never in a state of optimum conditioning. I believe speed limits should be set roughly on the median speed of the road, which will likely raise those "fringe" limits (say 40 when should be a 50) and reduce the ones which contain genuine danger, due to the different rounding criteria applied to 85th/50th percentile selections.

#4 - Traffic volume management is important as roads become busier (M42/M25 VSL are key implementations).

Social engineering is equally as important, particularly in communites who perceive a problem which affects their quality of life. Everyone should be a stakeholder (traffic engineers, Police, residents, councillors, motorists) but the priority should be attributed to each in the order I have listed.

A self-contradiction?
How can something be deemed to be reasonable when the majority of the population (on a motorway) regularly and safely demonstrate exactly what they think of the limit?

#1: If they are routinely ignored, and with safety, surely they are routinely unreasonably low?

#2 Setting a speed limit roughly to the median will have the effect of lowering the speed limit such that a significant percentage of drivers are often kerbed way below their optimum speed of travel, dumbing down driver attention?

#4: Agreed.

Especially at sites where speed surveys are seen to be in action. People drive surprisingly slowly through what they think might be a speed trap (speedo over-read plus a little bit 'just to make sure')

There is nothing to suggest that in _general_ speed limits are unreasonably low. We have to remember the probability of deaths at higher impact speeds increases, plus the high likelihood that there will still be people who travel above the higher limit. Enforcing with cameras should be done to prevent this.



Not neccessarily, there may very well be cases where the limit is raised, possibly smoothing out these anomalies where some speed limits are ridiculously high or low.

Remember with 85th percentile setting the limit must be rounded down to the nearest value (i.e 85th percentile speed = 58 would cause a 50 limit) but I believe 50th percentile limits must be rounded up, so even if the 50th percentile speed was say 46, it would cause a 50 limit, and any higher than 50 would result in a 60. (Someone please correct me if I'm wrong!)

Surely this is a fairer way of setting limits? I've read somewhere recently that the safest driver is also statistically at or around the 50th percentile speed. (will try to find source)

I'm sure we all agree that the probability and severity of injury increases with closing speed in a collision, but what of evidence that it increases the likelihood of an accident in the first place, do you have any? No accident, no injury!

I'd be interested to see any evidence you can find to support 50th percentile drivers being the safest, since everything I've seen points to something a little higher.

Assuming you are correct: this will be become a trade off with other factors, such as fatigue (reducing journey time will be of benefit) and other economic impacts.


One thing you might have overlooked is that the 85th/50th percentile rule applies to a derestricted road – no speed restriction. It is invalid to do apply this to an already speed limited road.

I'm sorry, but isn't this a bit - no, a LOT like shutting the stable door after the horse has bolted?
Taking a picture of a motorist exceeding the posted limit has NOTHING to do with making the road SAFE. By the time the NIP lands on the door step it could already be too late.
Anyone have any stats for NIP's delivered to motorists who killed anyone in between the offence and the NIP?
If everything we are told is true, then a significant number of drivers with NIP's should have had an accident by the time it arrived.

All a camera does is cause regular drivers of that route to slow briefly - usually at the last minute, for 100 yards then it's foot down to what they feel they are safe at (85%tile). For SPECS, it leads to tailgating to hide their plate behind the vehicle in front, and/or watching the speedo closely to avoid blipping, or the latest ruse, changing lanes between cameras because they believe this avoids detection. That's not COMPLIANCE with the limits, it's simple AVOIDANCE, and leads to stupid collisions which could be avoided by using police to identify STUPID drivers or setting reasonable limits.

If the government was really concerned with SAFETY and not REVENUE, then they would be looking for COMPLIANCE yet this rarely seems to be the case.

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Time to take responsibility for our actions.. and don't be afraid of speaking out!

They are routinely ignored by large numbers precisely because they are NOT reasonable, and for no other reason. The 30mph limit may be 'perfectly reasonable' on aggregate, but on wider streets at quieter times in better conditions it's ignored precisely because it's far too blunt an 'instrument' to keep pace with ever changing conditions.



Setting the speed limit to the median criminalises around half the drivers.

It also makes the speed limit a target.

It's a flawed and deadly idea that must be stopped.



According to roads minister Ladyman recently, speed limits should be set for valid safety criteria and generally for no other reason. For once he's right and I agree with him.

There are no 'stakeholders' in speed limit setting because safety is a science.

The very idea of giving residents a say in speed limits is very much akin to asking your neigbour to decide on your cancer treatment. It's a dangerously stupid idea that needs to be well and truly stomped on.

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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 probably read that in the propaganda put out by people who want to set speeds at the 50th percentile. There is a reason why they've been set at the 85th. Just think about it a bit.

From what I've read:

If the 50th percentile speed are in excess of the posted limit, the limit is generally raised.

If the 85th percentile speed are in excess of the posted limit, the limit is generally reduced.

Similarly, locking up rapists and muggers and murderers serves no purpose - the crime has already been committed, better to have police out there preventing crimes rather than just detecting them?

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COAST Not just somewhere to keep a beach.

A young loner on a crusade to champion the cause of the innocent, the helpless, the powerless, in a world of criminals who operate above the law.

Where that's done, it's wrong. Pure and simple.

Anyway, these measures remain 'aggregate' measures covering a length of road with varying conditions and different times of day with very different conditions. So even where the 85th percentile speed is say 40mph and the limit is set to , there will usually be places and times where 50 or even 60mph is a perfectly safe and appropriate speed within the limit - hence the need for intelligent and discretionary enforcement.

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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

In my experience, the vast majority of current speed limits are not reasonable. Hence they are routinely ignored by most normal, sensible people


And maybe some immigration restrictions would help... But that's another argument...


Eh? Motorists (the majority) should have the last priority? And TRAFFIC ENGINEERS (of all people, who take great delight in buggering up our roads) have first priority?

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Pecunia Prius Equitas et Salus

I think that's right - you may be confusing Traffic engineers with politicians. I equate real traffic engineers with the guys who actually go out and determine the flows in a system and work out a way of smoothing the overall system - like a documentary I once saw about the Hanger Lane Gyratory, a TE spent 3 months observing the traffic, changed the lights sequence and overnight a massive reduction in queues was experienced in the whole system.

Any traffic engineer who models the flows in a system at a desk and never observes the real life system, any traffic engineer who tries to take one system and fit it to all other systems, and crucially, any traffic engineer who decides that lights would be a good addition to a roundabout, should be boiled in their own juices.

Motorists? Ask their opinion? So the East-west motorist will say that to ease flow, the lights going east west (in the morning) and West-east (in the afternoon) should be perma-green. The north-south motorist will disagree. The motorist is at the end of the chain (or perhaps one step higher than the politicians ... single celled amoeba similarly occupy a higher status than the politicians) but they should have a right to reply, a right to challnge. The challenge would be met fairly and openly by a qualified traffic engineer (of the 1st sort, as the second sort will have all be reduced to tallow by this point) to explain why the system was designed as it was. Vox populi leads to the situation whereby a consensus of challenge from the motorist forces a re-examination of the design.

just my 1.5 Euro cents.

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COAST Not just somewhere to keep a beach.

A young loner on a crusade to champion the cause of the innocent, the helpless, the powerless, in a world of criminals who operate above the law.

it doesn't help the raped/mugged/murdered does it? Surely it's better to attempt to stop the crime happening in the first place?

I agree that traditional non-politicised traffic engineers are worthy of huge respect. I fear that they are a dying breed, however. These days there is huge political manipulation, even extending to the training given to new traffic engineers.

Motorist opinions and behaviour are crucially important, but they must be assessed in an impartial aggregate way (which, as it happens, is something that traditional traffic engineers did very well).

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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

Yes absolutely. But law enforcement is a balance between preventing offences and, if thats not possible, punishing the perpetrators after the event. Punishment never stops the crime happening and therefore doesn't help the victim, except for them to see that justice has been done.
Whether the threat of punichment actually deters is open to lengthy debate.....

It is also true that whilst they are in jail they are not mugging/raping/murdering another innocent victim.

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Save a cow - eat a vegetarian