Seat Leon 154mph A11
Discussion
Pete317 said:
Leaving aside the legality or wisdom of doing 154 mph on a public road, here's a little quiz for anyone who's interested:
You're doing 154 mph on an empty motorway when you see a car ahead in the distance doing half your speed, and you decide to slow down in case he does something silly.
So, when you're 150 metres from him, you apply moderate braking and decelerate at 4m/s^2
How fast are you going when you pass him?
(Pished)You're doing 154 mph on an empty motorway when you see a car ahead in the distance doing half your speed, and you decide to slow down in case he does something silly.
So, when you're 150 metres from him, you apply moderate braking and decelerate at 4m/s^2
How fast are you going when you pass him?
About 110mph but a decal rate of 4m/s2 is more consistent with firm braking (MfS description) and you wouldn't apply the brakes that hard in something like a leon at that kind of speed immediately.
I also wish to reiterate my point from my first post.
9pm, March. So likely dark, cold and wet. With traffic still about.
Zombie said:
Pete317 said:
Leaving aside the legality or wisdom of doing 154 mph on a public road, here's a little quiz for anyone who's interested:
You're doing 154 mph on an empty motorway when you see a car ahead in the distance doing half your speed, and you decide to slow down in case he does something silly.
So, when you're 150 metres from him, you apply moderate braking and decelerate at 4m/s^2
How fast are you going when you pass him?
(Pished)You're doing 154 mph on an empty motorway when you see a car ahead in the distance doing half your speed, and you decide to slow down in case he does something silly.
So, when you're 150 metres from him, you apply moderate braking and decelerate at 4m/s^2
How fast are you going when you pass him?
About 110mph but a decal rate of 4m/s2 is more consistent with firm braking (MfS description) and you wouldn't apply the brakes that hard in something like a leon at that kind of speed immediately.
I also wish to reiterate my point from my first post.
9pm, March. So likely dark, cold and wet. With traffic still about.
I also didn't stipulate a Leon, although I take your point about firm braking.
Nonetheless, I regret to inform you that your answer's way out.
Zombie said:
Pete317 said:
Nonetheless, I regret to inform you that your answer's way out.
Are you sure? - Not meant in an antagonistic sense, I just can't find another way of working it out based on the equations I know off hand.I'll let you know in a day or two if you haven't figured it out by then.
Zombie said:
Yer, you might be on to something there.
I'm not sober enough to contemplate it though!
I think it would have taken the car behind 3.5 seconds to reach the 123mph mark, at which the car ahead has moved another 120 meters ahead?I'm not sober enough to contemplate it though!
I wish I paid attention in maths, I bet it's calculus or something
At this rate the car will never get past and I'm not going to be able to sleep wondering how you could work it out.
Edited by routari on Sunday 7th August 00:25
janesmith1950 said:
If reaction time is 0.5 seconds at 154mph, you'll have travelled about 35m before you do anything at all.
Which is fine given that you can see clearly ahead for 300m.hora said:
154mph can't be safe. How can it? Public roads have debris, potholes even on motorways, diesel spill even if minor, etc.
Yet it is done, safely, in a place not far from here.surveyor_101 said:
so at 2.3 secs mr leon has traveled 158 metres before he has had time to react to anything! But yeh most folk can do it safely at 3am if the a11 traffic is light.
You can create a study to prove whatever you like. You know full well that people who are paying attention do not take 2.3 secs to react. Pete317 said:
Leaving aside the legality or wisdom of doing 154 mph on a public road, here's a little quiz for anyone who's interested:
You're doing 154 mph on an empty motorway when you see a car ahead in the distance doing half your speed, and you decide to slow down in case he does something silly.
So, when you're 150 metres from him, you apply moderate braking and decelerate at 4m/s^2
How fast are you going when you pass him?
I'll pass him at whatever speed I like. And keep your braking to yourself, at higher speeds cars slow appreciably by just lifting off.You're doing 154 mph on an empty motorway when you see a car ahead in the distance doing half your speed, and you decide to slow down in case he does something silly.
So, when you're 150 metres from him, you apply moderate braking and decelerate at 4m/s^2
How fast are you going when you pass him?
I used 240 and 120 kmh as easier to work out without calculator. 240 and 120 equals roughly 66 and 33 metres per second. Difference in speed is roughly 33 mps. So car going 66 and decelerating at 4 m a second per second will take 8 seconds to get down to same speed as car ahead. Average speed over those 8 seconds is 50 so distance travelled is 400 metres. Car in front will have traveled 8 X 33 = 264 m in the same time. But it starts 150 m ahead so it will be 414 m from where first car started to brake ie when the two cars are travelling at the same speed it is still ahead. As the first car is still decelerating then it never catches the second car.
routari said:
I'm as mathematically adept as a door hinge, but is the missing thing that the car ahead also moves at 77mph, so the 'deceleration' distance isn't 150m?
You're quite right.154mph is 68.44 metres/sec, so to lose half of that at a deceleration of 4 m/s^2 takes 8.55 seconds.
The average speed being 51.33 m/s over that period means the distance covered is 440 metres.
But, over the same period, the car ahead covers 34.22 * 8.55 = 294 metres.
And 440 - 294 = 146 metres, which means that when you're four metres behind the car in front you'll be down to its speed, so you will not pass it.
A simpler way is to say that your average speed over the 8.55 seconds is 17.11 m/s more than that of the car ahead, so the relative distance covered is 8.55 * 17.11 = 146 metres
I threw that in because some people, particularly those who really ought to know better, seem to have little or no appreciation of dynamics.
Edited by Pete317 on Sunday 7th August 11:31
janesmith1950 said:
If reaction time is 0.5 seconds at 154mph, you'll have travelled about 35m before you do anything at all.
From one of my expert reports:The Highway Code refers to this period as ‘Thinking Distance’ and calculates this distance using a reaction time of 0.67 seconds. It is generally accepted that such a time is too fast for normal traffic situations being more in keeping to anticipation. It's a reaction period which might be considered as being more appropriate when a driver is approaching a green traffic signal and anticipates it changing to red against them.
The Highway Code figure was 0.68 seconds until metric units were used. It is generally believed that the figure was determined not by test or research but more of a convenience as it related to a movement of one foot per mph and therefore easy to remember. [reference]
In normal road traffic situations where events occur unexpectedly in good daylight and in direct view of the driver a period of 0.75 to 2.0 seconds is considered to be more reasonable. Data typically shows that 90 – 95% of subjects responded within 1.5 seconds or less, although consideration must be given to the situation and other prevailing circumstances. [reference]
I see that the same thing happened recently on the M5 near Worcester. Mercedes E350 at 3 a.m.
http://worcesterobserver.co.uk/news/driver-caught-...
http://worcesterobserver.co.uk/news/driver-caught-...
I imagine a thinking distance relevant to driving isn't just some generic reaction test either. If you're on your driving test and your instructed shouted STOP out of nowhere, I imagine the delay would be longer than if he'd just told you that in a moment he's going to hit the dashboard with his clipboard and say stop, and so you're sitting there primed and ready to react to something you know is coming and you're being tested on.
In the second scenario you know that your reaction to a coming event is to brake hard. There's no thinking time of what your reaction to something unusual happening should be, and there's no reaction time needed for even know what the thing you need to weigh up is. 1.5 seconds sounds about right for something ahead that suddenly needs evaluating when you were just thinking about last night's curry.
The only thing going in the favour of someone doing that speed is that they're probably a lot more focussed on the road ahead, and anticipating something bad coming that they're more primed to react and lift to anything unknown, compared to someone sitting at 50 in a 50 thinking about work, or the delicious curry they're going to order tonight.
In the second scenario you know that your reaction to a coming event is to brake hard. There's no thinking time of what your reaction to something unusual happening should be, and there's no reaction time needed for even know what the thing you need to weigh up is. 1.5 seconds sounds about right for something ahead that suddenly needs evaluating when you were just thinking about last night's curry.
The only thing going in the favour of someone doing that speed is that they're probably a lot more focussed on the road ahead, and anticipating something bad coming that they're more primed to react and lift to anything unknown, compared to someone sitting at 50 in a 50 thinking about work, or the delicious curry they're going to order tonight.
agtlaw said:
janesmith1950 said:
If reaction time is 0.5 seconds at 154mph, you'll have travelled about 35m before you do anything at all.
From one of my expert reports:The Highway Code refers to this period as ‘Thinking Distance’ and calculates this distance using a reaction time of 0.67 seconds. It is generally accepted that such a time is too fast for normal traffic situations being more in keeping to anticipation. It's a reaction period which might be considered as being more appropriate when a driver is approaching a green traffic signal and anticipates it changing to red against them.
The Highway Code figure was 0.68 seconds until metric units were used. It is generally believed that the figure was determined not by test or research but more of a convenience as it related to a movement of one foot per mph and therefore easy to remember. [reference]
In normal road traffic situations where events occur unexpectedly in good daylight and in direct view of the driver a period of 0.75 to 2.0 seconds is considered to be more reasonable. Data typically shows that 90 – 95% of subjects responded within 1.5 seconds or less, although consideration must be given to the situation and other prevailing circumstances. [reference]
People tend to react much quicker to events which are at least anticipated than they would to completely unexpected events.
A driver driving past a school at chucking out time would probably react much quicker to events than if they were driving down a quiet motorway and a piano fell out of a plane and landed in front of them.
But at the kind of high speeds we're discussing here, where the braking time is around 10 seconds, talking about reaction time is rather moot.
agtlaw said:
I see that the same thing happened recently on the M5 near Worcester. Mercedes E350 at 3 a.m.
http://worcesterobserver.co.uk/news/driver-caught-...
People doing those sort of speeds is far from uncommon, particularly on arrow-straight sections of deserted motorway, which is presumably why they have these speed checks there.http://worcesterobserver.co.uk/news/driver-caught-...
There's a dual carriageway bypass about 100 metres from my office window, and I hear bikes going past at speeds well into 3 figures on an almost daily basis when the weather's fine.
Not seen any accidents in the 15 years I've been there though.
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