(Would you like the)Motorway speed limit to be raised to 130km/h

Mycroft H

bbk wrote: »

Which is why there is a debate about how fast we want idiots propelled into other users.

120km/h-130km/h is fast enough considering the standard Irish driver.

The flow of motorway can abruptly change in heavy traffic so it just takes someone to be pissing along at 140+km/h for accidents to happen.

(And yes I know the video is ancient but it still applies)

For what it's worth I'd be happier with a 100-110km/h limit during peak traffic near cities and a higher limit in rural/off peak situations.

Nino Brown

Wasn't there talk a few years back of dynamic speed limits on some Irish motorways? The speed was to be displayed on the information displays above the motorway depending on conditions. Maybe I just imagined it..

GTE

Nino Brown wrote: »

Judging by the speed that guy was driving in the video, I seriously doubt it would make any difference to him what the speed limit was. An idiot will be an idiot regardless of what a sign says.
What do you reckon the speed limit was in this video?

Not able to watch videos at the moment but if you're on about:
- The possibility that the driver would speed like that regardless
or.
- At high speeds, a crash is a crash and it doesnt matter what speed you are doing.

Well, the second point is what I am on about because I would be concerned at the increase in G force of rear ending someone at 140+ compared to 120.

GTE

Nino Brown wrote: »

Wasn't there talk a few years back of dynamic speed limits on some Irish motorways? The speed was to be displayed on the information displays above the motorway depending on conditions. Maybe I just imagined it..

I think that was mentioned very recently. I think it is on the way. It was announced along with the new regional road signage and audit of speed limits nationwide.

Nino Brown

bbk wrote: »

Not able to watch videos at the moment but if you're on about:
- The possibility that the driver would speed like that regardless
or.
- At high speeds, a crash is a crash and it doesnt matter what speed you are doing.

Well, the second point is what I am on about because I would be concerned at the increase in G force of rear ending someone at 140+ compared to 120.

I mean he was driving recklessly, the speed limit would be irrelevant to a driver like that, he would have been speeding anyway.
I know what you mean about G forces, but a higher speed limit doesn't absolve people of safe driving responsibilities, drivers are still expected to stay a safe distance behind other cars, and drive according to conditions. The idiots that don't do that, are probably already driving well above the speed limit. In a way increasing the speed limit only applies to responsible drivers.

GTE

Nino Brown wrote: »

I mean he was driving recklessly, the speed limit would be irrelevant to a driver like that, he would have been speeding anyway.
I know what you mean about G forces, but a higher speed limit doesn't absolve people of safe driving responsibilities, drivers are still expected to stay a safe distance behind other cars, and drive according to conditions. The idiots that don't do that, are probably already driving well above the speed limit. In a way increasing the speed limit only applies to responsible drivers.

Fair enough, and how people will speed with a higher limit is a big issue but lets just assume for now that the people who are driving on the imaginary roads we are all discussing (by that I mean with different speed limits to now) are going to be pretty lawful in the way they go about things.

From there, the safety issues of when a regular driver who is well under the limit of their abilities when cruising at 140 (hell, maybe even 120) is then faced with a situation which could show up their shortcomings whether it be ultimate attention being paid or their judgements. This is where my point about us reaching an ultimate speed limit in terms of the cars ability vs humans as a whole, but that sounds very Discovery Science channel for what is a very basic issue.

Mycroft H

bbk wrote: »

Not able to watch videos at the moment but if you're on about:
- The possibility that the driver would speed like that regardless
or.
- At high speeds, a crash is a crash and it doesnt matter what speed you are doing.

Well, the second point is what I am on about because I would be concerned at the increase in G force of rear ending someone at 140+ compared to 120.

It's more down to the average reaction time. A quick google shows me figures of 2.5 seconds.

That 2.5 seconds (all other things equal) would leave you travelling an extra 17m before you pushed the brakes. Is it enough to make a difference? I have no idea, but I would err on the side of yes.

Sam Russell

Mycroft H wrote: »

120km/h-130km/h is fast enough considering the standard Irish driver.

The flow of motorway can abruptly change in heavy traffic so it just takes someone to be pissing along at 140+km/h for accidents to happen.

(And yes I know the video is ancient but it still applies)

For what it's worth I'd be happier with a 100-110km/h limit during peak traffic near cities and a higher limit in rural/off peak situations.

Looking at the video, what started to happen before the pile-up was the lanes reversed. That is, the fast lane was travelling slower than the middle lane which travelled slower than the slow lane. The distance between vehicles also compressed, particularly in the fast lane. As a result, cars began switching lanes into spaces that did not exist untill one car spun causing panic.

That whole situation was caused by congestion, inappropriate speed, and undertaking.

GTE

Mycroft H wrote: »

It's more down to the average reaction time. A quick google shows me figures of 2.5 seconds.

That 2.5 seconds (all other things equal) would leave you travelling an extra 17m before you pushed the brakes. Is it enough to make a difference? I have no idea, but I would err on the side of yes.

Rather that it being more about one thing than the other, I think it is one leading to the other if you get me. Faster speed, more distance traveled for reaction time, bigger boom.

Mycroft H

bbk wrote: »

Rather that it being more about one thing than the other, I think it is one leading to the other if you get me. Faster speed, more distance traveled for reaction time, bigger boom.

Yea, your right. Proportionally longer braking distance then too at 140km/h.

Iwannahurl

Exponentially proportional. Braking (stopping) distance is related to the square of the speed when the brakes are applied.

Chimaera

The kinetic energy of an object increases with the square of its speed. The brakes have to dissipate this energy as heat, but it's a more complicated relationship (the energy dissipated as heat is roughly proportional to the square of the distance covered while stopping, but the diameter of the brakes vs the diameter of the wheels is a factor too [it's complex, OK?]).

But anyway, going from 120 km/h to 140 km/h (a 16.7 % increase) increases the energy you need to get rid of by 36.1 %. And you're going to travel an extra 13.9 m during a reaction time of 2.5 s. That's more than two car lengths.

CiniO

Chimaera wrote: »

The kinetic energy of an object increases with the square of its speed. The brakes have to dissipate this energy as heat, but it's a more complicated relationship (the energy dissipated as heat is roughly proportional to the square of the distance covered while stopping, but the diameter of the brakes vs the diameter of the wheels is a factor too [it's complex, OK?]).

It's not as complex as you are trying to present it.
Braking distance depends on square of the speed.
If you assume that car can stop in 10m from 50km/h, then it will stop from roughly 40m from 100km/h, or 160m from 200km/h, assuming brakes work efficient at all cases.
Diameter of brakes or wheels doesn't have much to it.

But anyway, going from 120 km/h to 140 km/h (a 16.7 % increase) increases the energy you need to get rid of by 36.1 %. And you're going to travel an extra 13.9 m during a reaction time of 2.5 s. That's more than two car lengths.

People with reaction times of 2.5s shouldn't be allowed driving.

Iwannahurl

Sam Russell wrote: »

Looking at the video, what started to happen before the pile-up was the lanes reversed. That is, the fast lane was travelling slower than the middle lane which travelled slower than the slow lane. The distance between vehicles also compressed, particularly in the fast lane. As a result, cars began switching lanes into spaces that did not exist untill one car spun causing panic.

That whole situation was caused by congestion, inappropriate speed, and undertaking.

I don't want to get bogged down in the details of that particular pile-up, but I can't help wondering what's going on with the white van that appears in the overtaking lane starting around 30 seconds in. Doesn't look right to me, but I can't see exactly what's going on.

Iwannahurl

CiniO wrote: »

People with reaction times of 2.5s shouldn't be allowed driving.

"To make highways reasonably safe, the engineer must provide a continuous sight distance ... equal to or greater than the stopping sight distance. As an integral part of the stopping sight distance, a value for the brake reaction time must be assumed. Extensive research has shown that 90% of the driving population can react in 2.5 seconds or less. The brake reaction time normally used in design, therefore, is 2.5 seconds."

http://www.webpages.uidaho.edu/niatt_labmanual/chapters/geometricdesign/theoryandconcepts/BrakeReactionTime.htm

CiniO wrote: »

If you assume that car can stop in 10m from 50km/h, then it will stop from roughly 40m from 100km/h, or 160m from 200km/h, assuming brakes work efficient at all cases.

GTE

Iwannahurl wrote: »

"To make highways reasonably safe, the engineer must provide a continuous sight distance ... equal to or greater than the stopping sight distance. As an integral part of the stopping sight distance, a value for the brake reaction time must be assumed. Extensive research has shown that 90% of the driving population can react in 2.5 seconds or less. The brake reaction time normally used in design, therefore, is 2.5 seconds."

http://www.webpages.uidaho.edu/niatt_labmanual/chapters/geometricdesign/theoryandconcepts/BrakeReactionTime.htm

Jaysus, I could be a bad racing car driver with my quick reactions compared to that.

But I think those figures are fairly right, we have such a wide demographic of drivers on the road for lack of a better word. In general I think we just are too close to eachother when driving.

CiniO

Iwannahurl wrote: »

"To make highways reasonably safe, the engineer must provide a continuous sight distance ... equal to or greater than the stopping sight distance. As an integral part of the stopping sight distance, a value for the brake reaction time must be assumed. Extensive research has shown that 90% of the driving population can react in 2.5 seconds or less. The brake reaction time normally used in design, therefore, is 2.5 seconds."

Is this not data from America??? Maybe they are just slower

Anyway - Even above text says that 90% of driving population can react in 2.5 seconds or less. As having exact result of 2.5 is nearly impossible, then 90% drivers can react in less than 2.5 seconds.


Some study here

Many studies have estimated the reaction time based on indoor experiments and driving sim-ulators. For example, in the study by Johansson and Rummer [9] more than 300 subjects were
instructed to brake a pedal as soon as they heard a sound. The estimated reaction time varied
from 0.4 second to 2.7 seconds with a mean value of 1.0 second.

So average is more likely 1 seconds. Not 2.5.

I sustain my previous statement that people with 2.5s reaction time shouldn't be driving.

Iwannahurl

CiniO wrote: »

Is this not data from America??? Maybe they are just slower

Anyway - Even above text says that 90% of driving population can react in 2.5 seconds or less. As having exact result of 2.5 is nearly impossible, then 90% drivers can react in less than 2.5 seconds.

Some study here

So average is more likely 1 seconds. Not 2.5.

I sustain my previous statement that people with 2.5s reaction time shouldn't be driving.

That paper refers to a 1971 study. The maximum reaction time was 2.7 seconds, and the mean was 1 second.

I prefer European studies myself. Here's one from the Dutch national road safety research institute, SWOV, which refers to the "two second rule": http://www.swov.nl/rapport/Factsheets/UK/FS_Headway.pdf

I believe that 3 seconds may be recommended in Sweden, but just now I can't find a reference to back that up.

The Pheasant2

Definitely would agree with this! Dual carriageways should be raised to 80 too

Chimaera

CiniO wrote: »

It's not as complex as you are trying to present it.
Braking distance depends on square of the speed.
If you assume that car can stop in 10m from 50km/h, then it will stop from roughly 40m from 100km/h, or 160m from 200km/h, assuming brakes work efficient at all cases.
Diameter of brakes or wheels doesn't have much to it.

I suggest you do some more reading on the topic.

Here's a good start: http://en.wikipedia.org/wiki/Friction#Energy_of_friction

If you assume that the friction force is constant (not a bad one in extreme braking) then the integral works out to be the friction distance (x) squared. This distance refers to the distance the friction material covers on the friction surface i.e. it's measured as the distance the pad travels over the disk. This is related to the distance covered over the ground by the ratio of the disk diameter to the tyre diameter. The net result is to somewhat linearise the energy increase effect.

Examining the braking distance data in Iwannahurl's post, you can see the increase in braking distance alone (not counting reaction time) is close to linear.

As for the reaction times: it's standard engineering practice to design for the worst-case scenario as this provides a larger margin of error. Do some reading on inherently safe design for more on this. The basic principle is you design safety into the system as much as possible to reduce the potential for the human element to do damage.

GTE

CiniO wrote: »

It's not as complex as you are trying to present it.

I think you are pushing it in that statement to say the very least.

Iwannahurl

bbk wrote: »

Jaysus, I could be a bad racing car driver with my quick reactions compared to that.

But I think those figures are fairly right, we have such a wide demographic of drivers on the road for lack of a better word. In general I think we just are too close to eachother when driving.

Cue one of my favourite videos on the subject:

https://www.youtube.com/watch?v=BpZRxo3EWAc

CiniO

Chimaera wrote: »

I suggest you do some more reading on the topic.

Here's a good start: http://en.wikipedia.org/wiki/Friction#Energy_of_friction

If you assume that the friction force is constant (not a bad one in extreme braking) then the integral works out to be the friction distance (x) squared. This distance refers to the distance the friction material covers on the friction surface i.e. it's measured as the distance the pad travels over the disk. This is related to the distance covered over the ground by the ratio of the disk diameter to the tyre diameter. The net result is to somewhat linearise the energy increase effect.

I disagree.
Brake pads have very little to do here, assuming they are efficient enough to use maximum braking force during braking from speed in question.

Examining the braking distance data in Iwannahurl's post, you can see the increase in braking distance alone (not counting reaction time) is close to linear.

Sorry, but it's not. Have a look at chart again.
Braking distance depansds on square of speed. It's shown very clearly at the chart.

As for the reaction times: it's standard engineering practice to design for the worst-case scenario as this provides a larger margin of error. Do some reading on inherently safe design for more on this. The basic principle is you design safety into the system as much as possible to reduce the potential for the human element to do damage.

Of course.
All I said was that drivers with 2.5 seconds reaction time shouldn't be driving.

Irish Steve

The vast majority of Irish drivers have never driven on a German Autobahn, which is probably just as well, as their speed limits in some cases are NO limit, and the quality of the roads is in some cases considerably lower than Irish Motorways, simply because the Autobahn are a lot older. I have driven on them, and on other European high speed roads, in a number of vehicles, and it's an interesting experience.

The other factor is that a lot of the vehicles in use on German Autobahn are well able to get to and sustain speeds considerably in excess of 120 Kph.

The harsh reality is that the tax system in Ireland has led to a lot of chronically underpowered vehicles being sold here, I have memories of a company supplied Mazda 626 that couldn't take the skin off a soggy rice pudding, I think it was 1.6, in a heavy body shell, and there are plenty of other examples out there, if you read the spec sheets of a number of vehicles, there are quite a few where the smallest engine size offered is only available in Ireland, and every other country has a larger engine as the minimum spec. That's entirely down to the tax and VRT system discriminating against engine size, and often, a larger engine can be more economic than the smaller size, simply because it's not working so hard.

I personally would like to see the speed limits on motorways removed, with the exception of the M50, which should be downgraded to an N road, and have a similar system to the M25, with variable speed limits controlled by overhead signs.

I'd also like to see American style barriers in the traffic lanes on the M50, to positively prevent the idiots that insist on going from Lane 4 across the hatchings on to the exit ramp, or who join in the same cavalier manner. Even better would be barriers that could be raised or lowered depending on queue lengths, and they would be aggressively used to stop the queue jumping crawlers who won't get into the queue for an exit, but crawl in lane 1 and then force their way in to the queue at the last possible moment, having delayed lane 1 in the process.

There would however be some caveats. The first would be that regardless of the actual speed involved, the person that caused an accident would be in court.

The second would be that some of the existing "standards" would have to be more aggressively enforced, and evidence from a dash cam could and should be used to take action without having to be witnessed by a Garda member. That might help solve tailgating, and also inappropriate lane use.

Higher speed limits would also help get rid of the "target" mentality, and also help make drivers more aware of their surroundings, as they'd have to recognise that (with few exceptions) there could be vehicles travelling at higher speeds, so regular use of the rear view mirror would be appropriate.

The reality is that way too many of the speed limits in general are bad. The old N2, now downgraded to an R status, has a long section that has a 60 Kph limit, and only a few years ago, with massively higher volumes, that same road was deemed safe enough for 100 Kph. Is the 60 a safety thing? I very much doubt it, my suspicion is that the 60 limit is more about trying to force people to use the motorway (in some cases like the old N3 to get the toll take up), or even more cynically, to enable local land owners to apply for planning permission on what was agricultural land on the basis that as it's now "in a speed limit", it can be rezoned or used for more valuable purposes. Road safety is a long way down the list on some of these cases.

I will be surprised if anything good happens with speed limits any time soon, there's just not the will, or in some cases the intelligence, to design and implement a good working system, so we are going to remain stuck with a mess that is very clearly not fit for purpose.

Such is life

Iwannahurl

CiniO wrote: »

All I said was that drivers with 2.5 seconds reaction time shouldn't be driving.

On what basis?

Consider the following scenario. Two motorists are driving identical cars in adjacent lanes. One is a driver with an average reaction time of 1 second (as per the study you linked), and he's travelling at 110 km/h. The other is a slow reactor, taking 2.5 seconds, and is travelling at 90 km/h. Something occurs up ahead that requires them to perform an emergency stop.

Here's how the stopping distance figures work out, based on the graph above:

110 km/h = 30.5m/sec. (30.5 x 1) + 104 = 134.5 metres.
90 km/h = 25m/sec. (25 x 2.5) + 70 = 132.5 metres.

The slower-reacting and slower-moving driver stops 2 metres earlier, if my sums are correct.

Of course the situation would be radically different if the slow reactor was driving faster, and vice versa, but that just serves to reinforce the basic point that driving more slowly is inherently safer.

Keeping speed optimally low is a one-size-fits-all strategy that makes the roads safer for everyone, whether fast or slow reactors.

CiniO

Iwannahurl wrote: »

On what basis?

Consider the following scenario. Two motorists are driving identical cars in adjacent lanes. One is a driver with an average reaction time of 1 second (as per the study you linked), and he's travelling at 110 km/h. The other is a slow reactor, taking 2.5 seconds, and is travelling at 90 km/h. Something occurs up ahead that requires them to perform an emergency stop.

Here's how the stopping distance figures work out, based on the graph above:

110 km/h = 30.5m/sec. (30.5 x 1) + 104 = 134.5 metres.
90 km/h = 25m/sec. (25 x 2.5) + 70 = 132.5 metres.

The slower-reacting and slower-moving driver stops 2 metres earlier, if my sums are correct.

Of course the situation would be radically different if the slow reactor was driving faster, and vice versa, but that just serves to reinforce the basic point that driving more slowly is inherently safer.

Keeping speed optimally low is a one-size-fits-all strategy that makes the roads safer for everyone, whether fast or slow reactors.

Yes, but the main problem is how are you going to convince person with 2.5s reaction to drive slower?

Also this graph must not be right, as modern car's braking distance from around 100km/h is more like around 40metres. Not 85m like on the graph. But it doesn't affect your logic anyway.

But look at it otherwise.
Person driving in dark at 80km/h with dipped lights on.
Assume his light lit the area 55metres in front of the car.
If his reaction time is 2.5 seconds, is he see any obstruction on the road (in 55 metres as his lights allow him to see it), in 2.5 seconds he will already travel 55.5 metres, so he will hit the obstruction without even doing anything.

vector

Voted YES,


because it would reduce the car travelling time between Cork and Dublin, which would hopefully hurt Irish Rail and their high prices!

Iwannahurl

CiniO wrote: »

Yes, but the main problem is how are you going to convince person with 2.5s reaction to drive slower?

Also this graph must not be right, as modern car's braking distance from around 100km/h is more like around 40metres. Not 85m like on the graph. But it doesn't affect your logic anyway.

But look at it otherwise.
Person driving in dark at 80km/h with dipped lights on.
Assume his light lit the area 55metres in front of the car.
If his reaction time is 2.5 seconds, is he see any obstruction on the road (in 55 metres as his lights allow him to see it), in 2.5 seconds he will already travel 55.5 metres, so he will hit the obstruction without even doing anything.

The graphs are based on aggregated data, I would imagine, and may well be based on 'worst case' assumptions. Presumably they will have to be updated over time, according to developing technology or whatever. Certainly that is happening with research into speed and related risks: the conclusions are not the same now as they were in the 1970s or even the 1990s.

With regard to reaction time, it is simply not possible to allow for all eventualities, and I don't think it is tenable to suggest banning all motorists with reaction times of more than 2.4 seconds. Or would that be > 2.4999999 seconds?

The same general criteria apply to the scenario you suggest, ie a person driving in the dark with dipped lights and encountering an obstruction in the road.

Firstly, that driver should be applying the 2 or even 3 second rule in the context of their own driving ability. That may mean driving more slowly when appropriate. Secondly, if the vehicle does hit an obstruction at 80 km/h the collision will be less severe than at, say, 100 km/h. Finally, if the vehicle is travelling at 100 km/h, the visibility ahead is 55 metres, and the driver's reaction time is 1 second, the vehicle will travel 28 metres after the obstruction is seen. That leaves 27 metres for the braking required to avoid the collision or reduce its severity. If a modern car's braking distance is 40 metres at 100 km/h as you say, that still leaves a 13 metre 'over-run'.

What might its speed be on impact? I don't know, but I think complacency about reaction times and stopping distances is not to be encouraged, human nature being what it is, and risk compensation being a well-known phenomenon.

Chimaera

The current information in the Rules of the Road (p.115) on braking distance comes from 2012 data from the TRL in the UK and shows rather shorter stopping distances than quoted earlier by Iwannahurl.

I disagree.
Brake pads have very little to do here, assuming they are efficient enough to use maximum braking force during braking from speed in question.

The brake pads are what turn the kinetic energy into heat. They have everything to do with how quickly you stop. The calculation for the energy dissipation includes this effect as the coefficient of friction term.

Sorry, but it's not. Have a look at chart again.
Braking distance depansds on square of speed. It's shown very clearly at the chart.

You'll find if you go back and read my post carefully that I said:

you can see the increase in braking distance alone (not counting reaction time) is close to linear.

Yes it's not quite linear, but it's not quite a square law either (it is close if you plot the data in excel and add a power trendline though). The TRL data the RotR use is more linear than the University of Idaho data Iwannahurl presented.

Interesting note on the reaction times though:
The UI data is based on a reaction time of 1.5 s.
The TRL data (being used by the RSA) is based on a reaction time of 0.72 s.

I personally think basing on a reaction time of 2.5 s is excessive, but I'd also worry that the 0.72 s is rather short. Most of us on a good day should react that fast or faster, but what if we're tired/sick/hugover/angry/etc?

I'll reiterate, I'm broadly in favour of higher motorway speed limits but subject to the concerns I posted earlier in the thread. I'm also in favour of having a debate based on data rather than speculation, and if there are data that contradict my opinion, so be it. Everything we do on the roads is a balancing act between our perception of risk and our desires to use the roads as we choose. The data serve to inform our perception of the risk and how we might choose to accomodate it.

unkel

Mycroft H wrote: »

Mein Deutsch ist nicht so toll. Summary?

Number of deaths on German roads has gone down from 22,000 to 3,000 in the past 40 years. There are still no speed limits on many Autobahns

Conclusion: (very) high speed on motorways does NOT kill