Speed Limit being a target

unkel

Ah-Watch wrote: »

I was failed for not going fast enough, doing 10-15 under the speed limit on an open road and not driving fast enough through towns.

Your driving instructor never told you to keep up your speed (if safe)? That's one incompetent driving instructor :eek:

dr.fuzzenstein

djimi wrote: »

To the best of my knowledge (and again I could be wrong; it wouldnt be the first time today) there is nothing in the rules of the road that tells you that you much stick to the speed limit. Its not a speed suggestion or a speed zone or something like that, its an upper limit that you are allowed to drive at. Now I agree that drivers should, where safe and possible, drive at a speed that is as close to the limit as possible so as to aid a good flow of traffic, but there is nothing in the ROTR to say you have to be within a certain percentage of the limit.

I think Stimpson has it bang on:

Avoid driving too slowly

In normal road and traffic conditions, keep up with the pace of the traffic flow while obeying the speed limit. While you must keep a safe distance away from the vehicle in front, you should not drive so slowly that your vehicle unnecessarily blocks other road users. If you drive too slowly, you risk frustrating other drivers, which could lead to dangerous overtaking.

Unfortunately there is too much of an attitude of "I'm a driving God and have a divine right and entitlement to be on the road and drive at whatever speed I like regardless of other road users".
If you are deliberatly going slow to hold other road users up and fail to let them pass, you could be done for obstruction.
So, no, you cannot decide what the speed on a certain stretch of road whould be and then enforce that, any driver should make an effort to keep up with traffic.

chasm

Also from the rules of the road

"Signed speed limits set the maximum speed at which vehicles [/B]may[/B]legally travel on a section of road between speed limit signs, assuming the vehicles are not restricted in any way.

The signs indicate the maximum speed at which your vehicle may travel on a particular road or stretch of road, not the required speed for the road"

http://www.rulesoftheroad.ie/rules-for-driving/speed-limits/speed-limits.html

corktina

theres nothing to say you have to do the limit but dear God, how do people drive so slowly on the motorways? I couldnt do 80 or 90 on them to save my life.

dr.fuzzenstein

chasm wrote: »

Also from the rules of the road

"Signed speed limits set the maximum speed at which vehicles [/B]may[/B]legally travel on a section of road between speed limit signs, assuming the vehicles are not restricted in any way.

The signs indicate the maximum speed at which your vehicle may travel on a particular road or stretch of road, not the required speed for the road"

http://www.rulesoftheroad.ie/rules-for-driving/speed-limits/speed-limits.html

Yes, absolutely right, you must not go over the speedlimit.
Just stick closely to it when conditions are grand.
And if you decide that you want to drive at 60 km/h instead of 100 km/h and no one's going to get past you, you can also get done.

Stark

bbk wrote: »

The further up the speed limits you go the less important it is IMO.
In slow speed limit areas like towns and city streets then I think making progress is very important. On a 100kph road though, you should be allowed to do 80-90 if you wish. On a motorway down to 100 should be fine.

Not if there's absolutely no reason to drive slowly and you're frustrating other drivers by driving 20km/hr below the speed limit. If it's a wide, straight stretch of good quality road, then it doesn't say much for the ability of the driver if they can't drive at 100 on it.

chasm

dr.fuzzenstein wrote: »

Yes, absolutely right, you must not go over the speedlimit.
Just stick closely to it when conditions are grand.
And if you decide that you want to drive at 60 km/h instead of 100 km/h and no one's going to get past you, you can also get done.

It says the maximum speed at which your vehicle may travel, Not "must".

The OP asked if the speed limit was a target, and i say no it is not, a limit means exactly that, the maximum permissible speed. I recall an argument before on boards where someone pointed out that if the limit has to be driven at or as close to, then cyclists would be expected to stay off the road, except in towns.

I agree 40kph below the speed limit is extremely slow, but most people i see who are driving below the limit are usually only 10-15kph below, if that. The thing is some people are never happy to be behind other cars whether they are doing the limit or not.

chasm

chasm wrote: »

It says the maximum speed at which your vehicle may travel, Not "must".

The OP asked if the speed limit was a target, and i say no it is not, a limit means exactly that, the maximum permissible speed. I recall an argument before on boards where someone pointed out that if the limit has to be driven at or as close to, then cyclists would be expected to stay off the road, except in towns.

I agree 40kph below the speed limit is extremely slow, but most people i see who are driving below the limit are usually only 10-15kph below, if that. The thing is some people are never happy to be behind other cars whether they are doing the limit or not.

Look there is no reason to be driving even 10 to 15km/h below the limit in most instances. I think it shows a lack of competence and driving ability and just lack of cop on not to keep up to the speed limit or a bit over it as you have to remember you speedometer tells you you are driving faster than you actually are by a few km/h.

It takes long enough to get places in this country on routes that don't have motorways without getting stuck behind people on a mission to slow down everybody behind them. I would safely say slow drivers add roughly 20 to 30 mins to my trip from Galway to Cork.

djimi

Brenna Delicious Patio wrote: »

Look there is no reason to be driving even 10 to 15km/h below the limit in most instances. I think it shows a lack of competence and driving ability and just lack of cop on not to keep up to the speed limit or a bit over it as you have to remember you speedometer tells you you are driving faster than you actually are by a few km/h.

Thats a ridiculously general statement. There are several 80kmph roads out my way that if I tried to go 80kmph or even close to it on them I would either wreck my car or end up in a ditch. Granted there are plenty of perfectly good straight roads where the limit feels quite slow, but there are an awful lot of country roads in Ireland where the speed limit is in excess of what would be considered a safe speed.

A speed limit is not there to tell you how fast you should be going. Its up to you as a driver to judge how fast you should be going. If a driver feels that, for any reason, going a certain speed is unsafe, then unless they are going excessively slowly then there is no reason why they should have to go faster than what they feel safe doing.

Just so were clear, I agree that drivers should make every effort to keep as good a pace as possible, Im not one for dawdling well below the speed limit so its not like Im trying to defend myself, but the way some people are going on in this thread youd swear just because a road has an 80kmph limit on it that is the speed you have to go or else all traffic is going to grind to a halt.

Anan1

bbk wrote: »

The further up the speed limits you go the less important it is IMO.
In slow speed limit areas like towns and city streets then I think making progress is very important. On a 100kph road though, you should be allowed to do 80-90 if you wish. On a motorway down to 100 should be fine.

I actually think the complete opposite. There are lots of urban areas where 50km/h is way too fast, whereas i've yet to see a motorway that can't easily take 120km/h.

GavRedKing

Its been mentioned already but the way I see it is, on a motorway if I can and if the conditions allow it, I will drive reasonalbly close if it not over the speed limit to a degree.

I always try and stay as close to the limit as I can, as I said if the conditions allow and if the road surface is sufficeint to allow safe travel at that speed.

chasm

Brenna Delicious Patio wrote: »

Look there is no reason to be driving even 10 to 15km/h below the limit in most instances. I think it shows a lack of competence and driving ability and just lack of cop on not to keep up to the speed limit or a bit over it as you have to remember you speedometer tells you you are driving faster than you actually are by a few km/h.

I'm sorry but after reading that i don't think i can take any other posts of yours on this thread seriously. Only for the fact that you have so many posts i'd have thought you were a troll!! Driving abit over the limit because your speedomer tells you you are driving faster than you actually are :rolleyes:

djimi

djimi wrote: »

Thats a ridiculously general statement. There are several 80kmph roads out my way that if I tried to go 80kmph or even close to it on them I would either wreck my car or end up in a ditch. Granted there are plenty of perfectly good straight roads where the limit feels quite slow, but there are an awful lot of country roads in Ireland where the speed limit is in excess of what would be considered a safe speed.

A speed limit is not there to tell you how fast you should be going. Its up to you as a driver to judge how fast you should be going. If a driver feels that, for any reason, going a certain speed is unsafe, then unless they are going excessively slowly then there is no reason why they should have to go faster than what they feel safe doing.

Just so were clear, I agree that drivers should make every effort to keep as good a pace as possible, Im not one for dawdling well below the speed limit so its not like Im trying to defend myself, but the way some people are going on in this thread youd swear just because a road has an 80kmph limit on it that is the speed you have to go or else all traffic is going to grind to a halt.

Well the problem is mostly encountered on N roads as these are generally the roads people use for getting from place to place and I will be more precise in saying leaving out towns and a few bad bends around buttevant there is no section of road between Cork and Galway where there is any need to at less than 100km/h, I have done the trip at 4am and sufficed to say I traveled the whole way comfortably at speeds well in excess of 100km/h.

djimi

Brenna Delicious Patio wrote: »

Well the problem is mostly encountered on N roads as these are generally the roads people use for getting from place to place and I will be more precise in saying leaving out towns and a few bad bends around buttevant there is no section of road between Cork and Galway where there is any need to at less than 100km/h, I have done the trip at 4am and sufficed to say I traveled the whole way comfortably at speeds well in excess of 100km/h.

I agree with you on those sort of roads, people should be trying to keep up with the speed limit where safe conditions allow on a long straight stretch of 100kmph road. The other side to that of course is that on those kinds of roads there is usually ample opportunities to overtake safely so its not always as much of an issue.

Brenna Delicious Patio wrote: »

Well the problem is mostly encountered on N roads as these are generally the roads people use for getting from place to place

Sorry but I had a bit of a chuckle at that; what else would people be using other types of roads for?!!

I jest; I know what you mean

djimi

djimi wrote: »

.

Sorry but I had a bit of a chuckle at that; what else would people be using other types of roads for?!!

I jest; I know what you mean

It looks slightly silly alright on re-reading.

chasm wrote: »

I'm sorry but after reading that i don't think i can take any other posts of yours on this thread seriously. Only for the fact that you have so many posts i'd have thought you were a troll!! Driving abit over the limit because your speedomer tells you you are driving faster than you actually are :rolleyes:

its common knowledge and has been discussed many times on this forum that your car speedometer reads a few km/h faster than you are actually travelling. This is easily confirmed using a sat nav.

Doylers

I have never gone 5km under the limit (except if I had to due to dangerous road conditions) I think it has to be said like above that not all road are suited to the limit. Out by me there is a bypass road that goes on the outskirts on waterford, the road is a dual carriageway with paths and the limit is only 60 but another country road by me has at least a turn every 2 mins hand it has a limit of 80 and the road is in pretty bad condition. Maybe road speed limits should be assessed individually per road and not just by type basis?

keithclancy

Brenna Delicious Patio wrote: »

its common knowledge and has been discussed many times on this forum that your car speedometer reads a few km/h faster than you are actually travelling. This is easily confirmed using a sat nav.

Here we go ... someones going to post that its not accurate, roads aren't flat .. blah blah blah ....

Why cant they have games builtin to cars that gives scores for overtaking, parking, average speed, flipping off grannies etc.

I can hear it now "Average speed 10 points ... smooth gearing 10 points... parallel parking ... ULTIMATE COMBO MEGA POINTS!!!"

chasm

Brenna Delicious Patio wrote: »

its common knowledge and has been discussed many times on this forum that your car speedometer reads a few km/h faster than you are actually travelling. This is easily confirmed using a sat nav.

I'm not going to get into a debate as to whether it is or not, it is the fact that you drive over the speed limit because of this.

stimpson

keithclancy wrote: »

Eh, he's right:

EU rules state:

* The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
* The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

djimi

stimpson wrote: »

Eh, he's right:

EU rules state:

* The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
* The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

That means the speedo may not be 100% accurate, not that it wont be 100% accurate. Unless youve had it tested and know for sure that its not producing an accurate reading, I think its a gamble to assume that its wrong.

One thing Ive always wondered about this arguement actually; people go on about the speedo being off compared to their SatNav; how do they know the SatNav is 100% accurate either, considering it is taking its reading from 20000 feet in space?

stimpson

djimi wrote: »

That means the speedo may not be 100% accurate, not that it wont be 100% accurate. Unless youve had it tested and know for sure that its not producing an accurate reading, I think its a gamble to assume that its wrong.

Car manufacturers err on the side of caution. I assume the poster has checked his speedo with satnav

One thing Ive always wondered about this arguement actually; people go on about the speedo being off compared to their SatNav; how do they know the SatNav is 100% accurate either, considering it is taking its reading from 20000 feet in space?

the simple answer: Maths.

the_syco

How slow is too slow? The RSA has drawn a line, and if you go under that, you fail. Otherwise some numpty going 15 in a 60 zone would pass.

=-=

As for satnavs, they usually take 3 satillites to get your position, and as well as that, there is usually a lag, so they may not give a corrent speed.

djimi

stimpson wrote: »

Car manufacturers err on the side of caution. I assume the poster has checked his speedo with satnav

the simple answer: Maths.

Do elaborate! Im not arguing; Im genuinely curious.

stimpson

djimi wrote: »

Do elaborate! Im not arguing; Im genuinely curious.

Well there are there are 30 GPS satellites in geosynchronous orbit (which means they move at the same speed as the earth) As they do not move relative to the earth we can rely on their position. They each have an atomic clock (accurate to 1 second every 300000 years) and beam signals back to earth with this time signal. Your GPS device picks up the signals of at least 3 of these. It then uses the difference between the signals to triangulates where on earth you are. With the signal from a 4th sat it can use error correction to improve it's accuracy even more. By looking at how your location changes over time it can calculate your speed (I believe to within 0.1 MPH)

keithclancy

stimpson wrote: »

Eh, he's right:

EU rules state:

* The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
* The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

I'm agreeing with him ... My would always 10%ish under what my speedo was reading.

Where as a Merc i used to drive before was bang on the money (think its something to do with the builtin sat nav being tied into the speed so it could tell you were exits are in tunnels)

However my tom tom and the merc sat nav were always the same

Doylers

stimpson wrote: »

Well there are there are 30 GPS satellites in geosynchronous orbit (which means they move at the same speed as the earth) As they do not move relative to the earth we can rely on their position. They each have an atomic clock (accurate to 1 second every 300000 years) and beam signals back to earth with this time signal. Your GPS device picks up the signals of at least 3 of these. It then uses the difference between the signals to triangulates where on earth you are. With the signal from a 4th sat it can use error correction to improve it's accuracy even more. By looking at how your location changes over time it can calculate your speed (I believe to within 0.1 MPH)

But the best of the signal is being used for military equipment. There also is an inaccuracy of a few meters. So if it thinks you traveled 2 meters when you actually did 4 the speed calculation would be wrong??

Did anyone try use a test mode on there cars odometer?? a digital one that is. I believe all fords can do it, but essentially you can put your digital odometer into test mode which will readout speed so you can compare to the main speedometer.

keithclancy

Doylers wrote: »

But the best of the signal is being used for military equipment. There also is an inaccuracy of a few meters. So if it thinks you traveled 2 meters when you actually did 4 the speed calculation would be wrong??

Did anyone try use a test mode on there cars odometer?? a digital one that is. I believe all fords can do it, but essentially you can put your digital odometer into test mode which will readout speed so you can compare to the main speedometer.

Did it on my scoda taking live ECU readouts, it was the same

stimpson

Doylers wrote: »

But the best of the signal is being used for military equipment. There also is an inaccuracy of a few meters. So if it thinks you traveled 2 meters when you actually did 4 the speed calculation would be wrong??

Did anyone try use a test mode on there cars odometer?? a digital one that is. I believe all fords can do it, but essentially you can put your digital odometer into test mode which will readout speed so you can compare to the main speedometer.

Consumer GPS devices can usually track up to 6 sats. And positional accuracy is not that important for measuring speed accurately.

GPS signals used to have errors built in to the signal to reduce the accuracy of civilian units to give the Us army a tactical advantage, but this was turned off in 2000.

GTE

Anan1 wrote: »

I actually think the complete opposite. There are lots of urban areas where 50km/h is way too fast, whereas i've yet to see a motorway that can't easily take 120km/h.

Two things really.

It should be assumed that drivers will drive at a speed appropriate to the conditions around him or her and not over the speed limit. So if some 50kph limits are indeed misplaced then a driver should recognise this and then go slower. My point is that under circumstances when a speed limit is genuinely acceptable progress is very important and driving at speeds far below that limit isn't advisable. Although I understand where you are coming from it doesn't really have much bearing on the thread since everyone should be driving to suit the conditions. I think thats clearly stated in the rules of the road anyway.

Secondly I wasnt saying the motorway cant take the speed, I dont think I ever mentioned that however I am on about the speed at which the driver wants to go. On a 120 kph stretch of motorway it is my opinion that this should be no lower then 100 kph. Aren't the bus and truck limiters in or around the 80 to 100 mark in the first place?

Stark wrote: »

Not if there's absolutely no reason to drive slowly and you're frustrating other drivers by driving 20km/hr below the speed limit. If it's a wide, straight stretch of good quality road, then it doesn't say much for the ability of the driver if they can't drive at 100 on it.

Most N roads where the 100 speed limit applies generally have stretches of road where overtaking is easy if the oncoming traffic is ok but that is the downside to single carriage way motoring. Again, bus and truck limiters are in the 80 to 100 range anyway.

Just in case its a question rolling though peoples heads I always drive at the speed limit where appropriate. I dont go on the motorway at 100kph or N roads at 80kph when I could be doing the speed limit but I have no problem coming across people driving 20 kph under the limit as on N roads its just the fact of life sometimes and on a motorway I can overtake.

Alun

Doylers wrote: »

But the best of the signal is being used for military equipment. There also is an inaccuracy of a few meters. So if it thinks you traveled 2 meters when you actually did 4 the speed calculation would be wrong??

GPS uses a totally different method for calculating speed, i.e. it does not, as many people assume, do a calculation based on distance travelled divided by time. Inherent in the very low level calculations performed to determine your position based on the raw satellite signals, it is necessary for the receiver to calculate the frequency shift due to the Doppler effect of the receiver travelling wrt the satellites and it uses this to calculate the speed. Most GPS manufacturers quote an accuracy for speed of 0.1m/s and it has been shown in tests that this rarely gets any worse than 0.2m/s. Interestingly, this level of accuracy is largely independent of the factors that adversely affect positional accuracy such as number of satellites in view and their geometry (i.e. how they are positioned and distributed in the field of view).