Article: Motorist fined R40,000

[Mike Hoxbig]

Increase speed limit to 120kmh around churches and help mankind speed up the evolution process.

Agreed!

 

[Romito]

Flamebait rejected....

Not talking about school roads, or any kinds of situations where schools, churches, etc are present,....

Oh I see you live outside of JHB so you have no clue what I am talking about.... that explains it!

I travel to JHB 3 times a week and spend my weekends there FYI!

 

[supersunbird]

I agree that you aren't reacting faster but it takes fractions of a second for an impulse to travel from your brain to your foot. Our reaction speeds are not great but 140kph is not exactly pushing our limits (obviously we're talking about on a freeway or something not in residential zones). Now 300 or higher there we're probably pushing limits, 140kph... nah.

What would you say is your time from taking your foot off the accelerator (depressed to stay at 140km/h) to starting to step on the brakes?

 

[porchrat]

What would you say is your time from taking your foot off the accelerator (depressed to stay at 140km/h) to starting to step on the brakes?

Well most nervous impulses have speeds that are measured in several 100 feet per second (some several 100 metres per second). Pain receptors are slower (single digit feet per second). Motor neurons are fast. Not the fastest (neurons that determine limb position relative to the rest of your body are faster for example at beyond 350 feet per second) but close. I'm don't recall the exact speed but a conservative estimate would be 250-300 feet per second.

Obviously your height matters because the taller you are the further the impulse needs to travel before it reaches your muscles to effect a response but looking at a figure of 250feet per second you can see that a person at say 5 foot is going to take 1/50th of a second to react. Maybe a little more because the first muscle fibres need a brief moment to begin contraction and of course your visual cortex needs to process the image and coordinate movements with the cerebellum (fine motor coords to program the set of movements required to move your right foot off the accelerator and onto the brake pedal (the last thing you want is to hit the clutch by accident )). Those happen pretty fast though most of it before you even consciously realise there is a problem.

The massive speeds your impulses move at are why even at speeds in excess of 300kph F1 drivers can hug so close to one another so as to be in the slipstream of the car in front and still react the vast majority of the time to avoid collisions.

EDIT: when I have time I'll check through my textbooks and see if I can find more accurate figures for motor neurons. I think my textbooks were metric as well... well... some parts .

 

[supersunbird]

Well most nervous impulses have speeds that are measured in several 100 feet per second (some several 100 metres per second). Pain receptors are slower (single digit feet per second). Motor neurons are fast. Not the fastest (neurons that determine limb position relative to the rest of your body are faster for example at beyond 350 feet per second) but close. I'm don't recall the exact speed but a conservative estimate would be 250-300 feet per second.

Obviously your height matters because the taller you are the further the impulse needs to travel before it reaches your muscles to effect a response but looking at a figure of 250feet per second you can see that a person at say 5 foot is going to take 1/50th of a second to react. Maybe a little more because the first muscle fibres need a brief moment to begin contraction and of course your visual cortex needs to process the image and coordinate movements with the cerebellum (fine motor coords to program the set of movements required to move your right foot off the accelerator and onto the brake pedal (the last thing you want is to hit the clutch by accident )). Those happen pretty fast though most of it before you even consciously realise there is a problem.

The massive speeds your impulses move at are why even at speeds in excess of 300kph F1 drivers can hug so close to one another so as to be in the slipstream of the car in front and still react the vast majority of the time to avoid collisions.

Erm, so with regards to my question what is the actions average time I may use in the calculation that you will be happy with: 0.5 seconds? 1 second? 1.5 seconds? 2 seconds?

If you want to you can give me an average time for your observation of say of an impending obstacle to actioning the start of the braking maneuver. But that is up to you.

 

[porchrat]

Erm, so with regards to my question what is the actions average time I may use in the calculation that you will be happy with: 0.5 seconds? 1 second? 1.5 seconds? 2 seconds?

If you want to you can give me an average time for your observation of say of an impending obstacle to actioning the start of the braking maneuver. But that is up to you.

I just told you that the neuron takes around 1/50th of a second to get the signal there. Sure it is a rough figure but it is in the ballpark. How does that translate into even half a second? We're looking at miniscule fractions of a second.

I would be exceptionally surprised if the rest of it added up to 0.5 seconds.

EDIT: Actually looks like most estimates of total reaction time from observing obstacle to hitting pedal are about 0.7 seconds. Longer than I would've expected. Amazing.

 

[supersunbird]

I just told you that the neuron takes around 1/50th of a second to get the signal there. Sure it is a rough figure but it is in the ballpark. How does that translate into even half a second? We're looking at miniscule fractions of a second.

I would be exceptionally surprised if the rest of it added up to 0.5 seconds.

EDIT: Actually looks like most estimates of total reaction time from observing obstacle to hitting pedal are about 0.7 seconds. Longer than I would've expected. Amazing.

So now I will use 0.7 as the response time:

100km/1uur
100 000/3600
27.7m/s
0.7 x 27.7 = 19.39m covered by time brake is pressed


120km/1uur
120 000/3600
33.3m/s
0.7 x 33.3 = 23.31m covered by time brake is pressed


140km/1uur
140 000/3600
38.8m/s
0.7 x 38.8 = 27.16m covered by time brake is pressed


200km/1uur
200 000/3600
55.5m/s
0.7 x 55.5 = 38.85m covered by time brake is pressed

So 40km/h above a 100 makes almost an 8 metres differerence just in the response time. Go measure 8 metres out and just check out how much that is from a bit further away.

Now one can also work out the time and rate of deceleration during braking and such but physics is and has never been my strongpoint but I'm sure that also means a much longer braking distance and a longer time for it to happen and thus a much longer distance is covered. A few year ago we also worked out the physics of what you would weigh during a car acccident and it was horrendous and your body and the car has to absorb that. If I have time over the weekend I'll try to do some calculations although that not my strong point.

 

[porchrat]

OK for sure more distance covered. Nobody said there wouldn't be. Provided you're on a freeway 8m is absolutely nothing. (and on a freeway you're actually comparing 120 to 140 so it is actually more like just under 4m... which is even more insignificant than absolutely nothing... it is absolutely absolutely nothing)/

 

[supersunbird]

OK for sure more distance covered. Nobody said there wouldn't be. Provided you're on a freeway 8m is absolutely nothing. (and on a freeway you're actually comparing 120 to 140 so it is actually more like just under 4m... which is even more insignificant than absolutely nothing... it is absolutely absolutely nothing)/

That 4 metres is a car length, and that 4 metres happens while absolutely nothing happens except moving closer to whatever is the problem. And 0.7 is more a optimal response and I think a average between 1 to 1.5 second would be more accurate.

Here are some interesting links I've found
http://www.visualexpert.com/Resources/reactiontime.html
http://www.sdt.com.au/safedrive-directory-STOPPINGDISTANCE.htm

Hene, look at those stopping distances and most of those are performance cars...

 

[porchrat]

That 4 metres is a car length

Yes which on a freeway is not very much. If you're sitting bunched up behind someone doing 140kph to the point at which that 4m matters then you need your license taken away.

Here are some interesting links I've found
http://www.visualexpert.com/Resources/reactiontime.html
http://www.sdt.com.au/safedrive-directory-STOPPINGDISTANCE.htm

Hene, look at those stopping distances and most of those are performance cars...

So I see thanks for finding those for us.

 

[dj_jyno]

This isn't just about speeding. It's about breaking the law, however lame you might think it is. Driving on an empty freeway at 200+ km/h today could turn into drunk driving tomorrow, and crashing into someone because you didn't see the need to stop at a stop sign the day after that. There seems to be a total disregard for the rules of the road among South African motorists these days.

Yesterday afternoon I saw 4 (yes, four) people ignoring stop signs within 4 minutes, at different intersections.