Speed Limits based on The 85th Percentile

[Panda]

I read a post earlier where it was suggested that basing speed limits on the 85th Percentile was rubbish, so I though I would do some reading on the subject (quiet night shift)

Do a Google search on 85th Percentile and you will find a lot of links, but to avoid people thinking that I copied information from some fruitcakes website I have taken some snippets of information from this site which is a report for the U.S. Department of Transportation Federal Highway Administration. There were many other government websites (not only in the U.S.) advocating the use of the 85th Percentile system. Check it out, there is a lot of credible research using testing criteria generally agreed to be accurate.

...The objectives of this research was to determine the effects of raising and lowering posted speed limits on driver behavior and accidents...

...The majority of motorists select a speed to reach their destination in the shortest time possible and to avoid endangering themselves, others, and their property. In selecting their speed, motorist consider roadway, traffic, weather, and other conditions. The collective judgment of the majority of motorists represents the level of reasonable travel and acceptable risk. Prior research has shown that the upper region of acceptable risk is in the vicinity of the 85th percentile speed...

...Most traffic engineers believe that speed limits should be posted to reflect the maximum speed considered to be safe and reasonable by the majority of drivers using the roadway under favorable conditions. Procedures used to set speed limits have evolved through years of experience and research...

...it is believed that raising the speed limit increases speeds and accidents...

...Speed limits were posted, on average, between 8 and 26 km/h below the 85th percentile speed...

...Lowering speed limits by 8, 16, 24, or 26 km/h at the study sites had a minor effect on vehicle speeds. Posting lower speed limits does not decrease motorist's speeds...

...Raising speed limits by 8, 16, or 25 km/h at the rural and urban sites had a minor effect on vehicle speeds. In other words, an increase in the posted speed limit did not create a corresponding increase in vehicle speeds...

...Raising speed limits in the region of the 85th percentile speed has an extremely beneficial effect on drivers complying with the posted speed limits...

...Lowering speed limits in the 33rd percentile speed provides a noncompliance rate of approximately 67 percent...

...Accidents at the sites where speed limits were lowered increased by 5.4 percent...

...Accidents at the sites where speed limits were raised decreased by 6.7 percent...

...Lowering speed limits more than 8 km/h below the 85th percentile speed of traffic did not reduce accidents...

...Based on the sites examined, it is apparent that the majority of highway agencies set speed limits below the average speed of traffic as opposed to setting limits in the upper region of the minimum accident risk band or about 85th percentile speed. This practice means that more than one-half of the motorist are in technical violation of the speed limits laws...

I have modified some of what I have copied and pasted here (kilometres instead of miles etc), but I have not changed the intent of the sentences.

What are other peoples thoughts on the 85th Percentile approach to speed limits.

Panda

[S3SR]

yeah i like that more than giving idiots 10%

but its all common sense obviously if your traveling on a 60kmh road and are overtaking ever car at a constant rate, your speeding or your speedo is out or everyone is slowing down.

put it this way ive been past a mob of maybe 30 cops sitting and waiting with a radar pointed at me, ive got cruise control on and i always set it to just above 60kmh so maybe 61/62 from what i can see and have never got in trouble not even pulled over.

theres no reason for speeding and the 10% leway is stupid, theres no excuse to speed on the streets they call those places a track. dont push your luck either im a cop in about 1yr or so ill book you all for doing 61kph.....never mind leway....lol :thebirds:

[Panda]

Originally Posted by FALCONSR

...im a cop in about 1yr or so ill book you all for doing 61kph...

See you in court

Panda

[Falcon Coupe]

Originally Posted by FALCONSR

dont push your luck either im a cop in about 1yr or so ill book you all for doing 61kph.....never mind leway....lol :thebirds:

You will go far as a cop with that attitude Hero. _

[Outbackjack]

If nothing else, all this discussion about 85 percentile and attitudes to speed has made all of us a lot more aware of our driving habits. This is a good thing, me thinks.

Perhaps if Governments encouraged more disscusssion like this, we wouldn't have to put up with these draconian laws that keep creeping in. Just my 2 cents.

One cent after tax!!

[XRQTR]

I find it interesting that there are tests out their, true tests, that show that slowing drivers down does not decrease accidents but in fact has the opposite effect, but more importantly that speeding them up actually goes to decreasing the number of accidents.

What I do find interesting though, although it doesn't surprise me, is that we have all these police ministers and government officials and even some saying they have done research to show that slowing traffic does decrease accidents. Where are they getting these stats from is what I would like to know, perhaps the likes of ACA and TT should try to get these studies and there authors on the show and then see what the ministers have to say about it then, although 4 corners might do a better job the other two have a larger viewing audience.

I agree with slowing traffic in places such as school zones, but who the hell decided that slowing places like Bridge Rd or High St to 40km/h would be of any benefit, are they saying that people around their are as silly as little children. To top it off this is imposed on us for at the very least 12 hours a day, why not do that around schools or aren't children as important as shoppers??

This just goes to show that freeways such as the Geelong freeway, or even the Hume Highway at points could and should be bumped up to 120-130km/h, at the least in the far right lane, kind of like the German Autobahn.

Just another couple of cents (no tax, cash mate cash :evilsasmo )

[Bill_R]

Originally Posted by XRQTR

I find it interesting that there are tests out their, true tests, that show that slowing drivers down does not decrease accidents but in fact has the opposite effect, but more importantly that speeding them up actually goes to decreasing the number of accidents.

In many cases where you slow drivers down far too much out of synch with conditions you distract them - they are always checking that speedo instead of focusing on the road.

Drivers also need to be taught about the "3 second rule" and there needs to be preference taken over enforcing a law against tailgating instead of speed revenue raising.

[Auslandau]

Originally Posted by FALCONSR

put it this way ive been past a mob of maybe 30 cops sitting and waiting with a radar pointed at me, ive got cruise control on and i always set it to just above 60kmh so maybe 61/62 from what i can see and have never got in trouble not even pulled over.

theres no reason for speeding and the 10% leway is stupid, theres no excuse to speed on the streets they call those places a track. dont push your luck either im a cop in about 1yr or so ill book you all for doing 61kph.....never mind leway....lol :thebirds:

Well if you set your cruise at that speed .....in Vic you would have been pinged by a speed camera. That would look good on your resume. Variation would have taken care of that if it crept up by 1-2kmh. Which they always do!

This is the mentallity of the new police force we are getting in Aust........ :



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[XA-Coupe]

Originally Posted by auslandau

Well if you set your cruise at that speed .....in Vic you would have been pinged by a speed camera. That would look good on your resume. Variation would have taken care of that if it crept up by 1-2kmh. Which they always do!

This is the mentallity of the new police force we are getting in Aust........ :

Remember that the police don't set the tolerances, it's set by the government , the cops just get the bad PR for it.

[Auslandau]

Originally Posted by XA-Coupe

Remember that the police don't set the tolerances, it's set by the government , the cops just get the bad PR for it.

Yep they do. I was refering mainly to the second section. This statement not required!

dont push your luck either im a cop in about 1yr or so ill book you all for doing 61kph.....never mind leway....lol



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[Bill_R]

Originally Posted by auslandau

dont push your luck either im a cop in about 1yr or so ill book you all for doing 61kph.....never mind leway....lol

Mate, you'll be doing paperwork, fetching coffee and running errands for a very long time. If you are lucky, you might walk the beat now and then.

[nugget378]

Originally Posted by XA-Coupe

Remember that the police don't set the tolerances, it's set by the government , the cops just get the bad PR for it.

Does the policy apply in vic where police have discretion to issue a warning instead of fine? seems this would be a way around a silly law like this in quite a few cases,for a fair minded person..

[Auslandau]

Originally Posted by nugget378

Does the policy apply in vic where police have discretion to issue a warning instead of fine? seems this would be a way around a silly law like this in quite a few cases,for a fair minded person..

Total discretion. The cameras dont



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[VelocityXR6TUte]

Originally Posted by FALCONSR

put it this way ive been past a mob of maybe 30 cops sitting and waiting :

30 cops to operate a radar trap

Thats our tax dollars being maximised, must only be speed limit offenders in that part of the world :

[jabba]

Originally Posted by FALCONSR

dont push your luck either im a cop in about 1yr or so ill book you all for doing 61kph.....never mind leway....lol :thebirds:

****er

[XA-Coupe]

Even if this 85th percentile stuff did wash, there would always be people going faster and in victoria, the leeway will still be insufficient. The real issue won't disappear.
FalconSR, I suspect your tenure as a cop, if you do indeed make it, will be short.

[Panda]

Originally Posted by XA-Coupe

...there would always be people going faster and in victoria, the leeway will still be insufficient...

It should be these people who are targeted

Originally Posted by FALCONSR

...anyways you were speeding so i have every right and youd lose in court...

I fear you would be embarrased in court, if your superiors allowed you to proceed with it.

Originally Posted by GMH8TR

...Speed limit freaks tend to upset the natural rythm that many roads have and I think that those people seem to easily fall into a complacent disposition as they believe that so long as they travel 10k's below, they can do no wrong and will get home safe...

Yep, don't use blinkers, talk on mobile phone etc - but as long as they are not speeding they are driving safely.

I think it is inevitable that many people focus on speed instead of other safe driving practices, we are taught that it is the cause of accidents so that the government can justify more cameras

Originally Posted by XRSIX-T

...I have seen the stats and the idea's which would halve our road accidents over night. Sadly you will never see them, at least not while the Government is structured the way it is...

Speed cameras mean more to the government than mere safety devices

Panda

[Bill_R]

You need to question some limits when everyone (including grandpas and grandmas) on stretches of road in this area (Nthn NSW - 20 km south of Qld border) are doing well in ecxess of some limits. What it leads to when you do the limit is some seriously dangerous tailgating.

I'm all for speeds that are relative to conditions. In many cases, the posted 50 or 60 km/h is way too high.

[TwistedEL]

Bill R: That would be the "2 second rule"

XRQTR: It is only illegal to hog the right lane if you are in a speed zone above 70, or it is sign posted Keep Left Unless Overtaking
And if I come up behind someone in a 100 zone going slower than the rest of the traffic I will let them know about it until they move or I find a suitable gap

[Bill_R]

Originally Posted by TwistedEL

Bill R: That would be the "2 second rule"

It's actually a 3 second rule. I was brought up on 2 seconds but now, in NSW, the recommendation in the handbook issued prior to sitting for a driving test is 3. Less than 1 second is an immediate fail.

[XRQTR]

Originally Posted by TwistedEL

XRQTR: It is only illegal to hog the right lane if you are in a speed zone above 70, or it is sign posted Keep Left Unless Overtaking
And if I come up behind someone in a 100 zone going slower than the rest of the traffic I will let them know about it until they move or I find a suitable gap

I don't care about the 50 and 60 zones, they are generally cruisey areas so no skin their, I am in fact talking about 70 plus zones, mostly 80 plus and the Freeways and Highways.

As for people moving, bud i am in a tow truck most of the time and they just look at you as if you are some kind of hoon or just trying to be intimidating because you have a bigger vehicle, the amazing thing is that they move quite quickly when I'm in the car, go figure.

[GCFordChic]

Arbitrary, unrealistic and nonuniform speed limits have created a socially acceptable disregard for speed limits. Unrealistic limits increase accident risks for persons who attempt to comply with limit by driving slower or faster than the majority of road users, Unreasonably low limits significantly decrease driver compliance and give road users such as person not familiar with the road and pedestrians, a false indication of actual traffic speeds.

Unrealistically high speed limits increase accident risk for drivers who are inexperienced or who disregard the basic speed law. Unrealistic limits also place enforcement officials and judges in the position of subjectively selecting and punishing violators. This practice can result in punishing average drivers, as well as high-risk violators.

The data collected during this study indicate that there are no benefits, either from a safety or operational point of view, from establishing speed limits less than the 85th percentile speed. This does not mean that all speed limits should be raised.

Just another few interesting quotes from that article, that I think people should note incase they dont read the whole thing.

[XA-Coupe]

Let me put it this way, I had more people get warnings for stuff than tickets given out. Usually based on the attitude test. I also had people turn a minor warning into a ticket or two for being a***holes.
The problem is that people don't run to the forum and say ' this copper gave me a warning!! ' they just run on to cry rivers when they get busted.
If there were 30 cops around a radar trap it woudl be a training exercise, in fact.. I can't think of 30 cops even there.. I suspect there may be a bucketload of exaggeration involved here.
Anyway, this is supposed to be about the 85th percentile and it's merits...

[S3SR]

Originally Posted by XA-Coupe

If there were 30 cops around a radar trap it woudl be a training exercise, in fact.. I can't think of 30 cops even there.. I suspect there may be a bucketload of exaggeration involved here.
Anyway, this is supposed to be about the 85th percentile and it's merits...

actually there honestly was and more up the side road

as for me booking it was a joke, smile morons : ... anyways you were speeding so i have every right and youd lose in court

thats all from me

[nugget378]

Originally Posted by FALCONSR

actually there honestly was and more up the side road

as for me booking it was a joke, smile morons : ... anyways you were speeding so i have every right and youd lose in court

thats all from me

It was'nt your first post of that type,I bet if there was a moron vote between you,and the people you called morons,you'd lose :thebirds:

[Scott]

The biggest thing in my mind that causes accidents is complacency of those behind the wheel. I generally find that I drive at a speed which feels natural for the conditions. Most of the time (in town) that speed is around the speed limit - maybe a little under or sometimes a little over. Speed limit freaks tend to upset the natural rythm that many roads have and I think that those people seem to easily fall into a complacent disposition as they believe that so long as they travel 10k's below, they can do no wrong and will get home safe.

[GCFordChic]

Originally Posted by GMH8TR

... I generally find that I drive at a speed which feels natural for the conditions. Most of the time (in town) that speed is around the speed limit - maybe a little under or sometimes a little over. Speed limit freaks tend to upset the natural rythm that many roads have and I think that those people seem to easily fall into a complacent disposition as they believe that so long as they travel 10k's below, they can do no wrong and will get home safe.

Your comment is a great summary of what the report found. Whether they increased or decreased the speed limit, the average speed in that area stayed around the same because people tend to drive at the speed they find appropriate once they evaluate the surroundings.

I think 85th percentile speed limits are a logical and enforceable measure. But in school zones and suburban areas the limits currently in place should stay the same.

[T_Terror]

Interesting report.

Makes sense and sounds logical...

which is why it will never be implemented by any current australian governments.

[XRSIX-T]

Hello people,

Don't worry about FALCONSR with any luck he'll be stationed out west and he'll grow a brain soon enough.

In relation to the speed topic just look at Germany, if you build the roads right the first time everything else falls into line. I work for the Dept. of Qld Transport I have seen the stats and the idea's which would halve our road accidents over night. Sadly you will never see them, at least not while the Government is structured the way it is.

I like to drive fast and street race and all the silly things but I think first about where I am an my surroundings first. 3am on quiet road away from houses, we can all have the same fun just be smart about it.

[XRSIX-T]

I agree Panda, speed cameras catch approx 90% of people who are only just over the limit. These are just every day safe divers just trying to get to where they need to go. If the government spent the same amount of money on our roads that they spent on the development, implementation and running of speed cameras, our roads would be much safer. I would rather see a cop in his car driving around than a stationary vehicle taking happy snaps. Well maybe not our freind Mr FALCONSR.