juan

I thought bullbars had been made illegal now. I still see em on the odd vehicle but nowhere near as much as 6 or 7 years ago

tiggers

Looking out the window into the company car park I can see three 4x4's all with bull bars on the most recent being W reg. Fortunately I don't work directly with these cretins.

tiggers

DTurn

Thought I'd post my thoughts on the subject, as someone working in accident reconstruction. As many posters have remarked, reaction time comes into the calculation. The Highway Code uses a reaction time of about 0.68 seconds. Allegedly this came from research, but it's probably more liekly that it makes it easy to remember reaction distances: 1 foot per mph of speed. This is actually a bit of an underestimate - most real life reaction times are in the range 3/4 to 1 1/2 seconds. Anyway, if you are travelling 5 mph faster, then you will cover a further 5 feet while you are thinking about braking.

After you've reacted to the hazard, the figure quoted assumes that you then lock the tyres on the car. Tests in everything from a Rover Metro to a Caterham 7 (that was fun - it locked the rear wheels first at 85 mph) show that no matter how good the tyres and braking equipment on your car, once the wheels are locked, you decelerate at about 0.7G. Depending on the ABS/tyre combination, you can get over 1G deceleration. A good threshold braker can get similar rates of deceleration. The Highway Code calculations use a deceleration rate of about 0.67G.

Anyway, if you plug the numbers in, at 35 mph, it takes a further 15 1/2 feet to stop if you lock all the wheels. Add the two extra distances together and you get 20.5 feet (hence 21 feet in the ad).

A few other points have been raised. The ad shows the rear wheels are still turning. This is typical of all modern cars and is due to pressure reduction in the rear lines. The European car construction rules make this a stipulation of type approval. If the rear wheels lock and the front ones don't the car would be unstable (the equivalent of a handbrake turn). Tests have shown that even with such braking systems, and no ABS, the rate of deceleration with locked front wheels is around 0.7G.

juan

Thanks for clearing all that up DTurn.
Wonder how our friend who started the the thread managed such amazing times?

Elvis Presley

It all comes down to judgement.

We need better drivers on the road, not just slower drivers.
People should be able to judge safe speeds themselves, not have to be told.

There are so many terrible drivers on the road. The driving test should be far more difficult, and there should be retests every 5 years. I realise it would be a pain in the ****, but accidents, congestion, road maintainence costs etc would all be reduced. More people would use public transport also so the servies would improve.

Hoppy

Thanks Carl, and Elvis, on reaction time. The way I read the ad and how I measured the extra distance was that reaction time had nothing to do with it. However, I can see that it is a factor.

But on the other hand, it only took me 30ft in total to stop from 30mph, although that's a very rough estimate as I only paced it out. So add couple of feet more to my six feet if you like. We're still nowhere near 21 feet.

And I don't buy this "worst case scenario" excuse. The ad clearly talks about THIS car stopping on a bright, dry day. There was no black ice or freezing fog.

I remember Jeremy Clarkson did a Top Gear thing on stopping distances and compared them to the highway code and how quickly an old Ford Anglia or something could stop and a few fast cars. The differences were huge, obviously. But his concluding line was a memeorable one. He said, "if you're going to step out in front of a car, make sure it's a fast one."

Richard.

Mathew

if a car stopped from 100mph to zero in 4seconds what would the decelerating g force? its been too long since I did any physics.

carl

Just over 1g.

Andrewza

Looks like 1.14G to me, but yes just over 1G

richs2891

Elvis I could not agree with any more !!
As an active member of the IAM I'm astounded by the driving abilities of the muppets that I see every day on the daily 2 mile commute to work.
The goverment needs to do something drastic and fast about this as soon as possible, but of course its not a vote winner so nothing gets done!

Why is it always drivers of old badly maintained cars that drive far too close, speed etc.

Robertio

iTrader: (1)

It's a shame the search is not working as there was a thread about this when that advert first appeared.

Like Hoppy I tried breaking from 30mph, I did a run in both directions on a damp road with cold brakes and was still miles inside the figures quoted.

Assuming you pick the same point to brake from, then surely both distances already include your reaction time? i.e. you register the front of your bonnet is level with the lampost and then react to break. Admittedly your reaction time will be better than in an emergency situation as you know that you are going to have to brake hard at a given point, but the difference wont be that much (IMHO).

BTW, I guess my old VTR didn't have to go through type approval as more than once I managed to lock all 4 wheels (admittedly from a fair bit more than 30)

MrData

I guess that while there are older cars on the road with crappy brakes, then the braking distances will have to reflect the worst scenario.

My mate had an idea once where all old cars over 10 years old were taken off the road Especially the Montegos and Maestros.

It's unfortunately the same with speed limits. Somehow, the limit should befit the vehicle doing the speed.

I recall a test on Top Gear once where they showed that a Porsche Carrera could accelerate to 60 and stop again in less than the published thinking distance for that speed.

My hope is that if I stray into the road accidentally it will be into the path of a performance car, rather than a corolla or a Morris Minor.

I remember seeing an old Cadillac at an auto show. The driver commented on how a 2 ton car simply had no hope of stopping with it's drum brakes. Yet still such cars are road legal??

Regards
Kurt

Joseph

Has anyone noticed that the rear wheels of the car are still turnong after it hits the pedestrian?
I find it strange and not suprising that it takes it so long to stop.
J.
Anyway 35 mph is too fast for that car and should be limited to 25mph.

Scooby_Maxus

[Parent mode]

Tiggers-

So let me get this straight, a prat drives too fast, breaking the law, hits a child out playing, kills the child and it’s the parents fault!

What a pile of..............

I guess you were all most careful as kids and never followed a ball into a road? Right?

Kids don't think- that’s the point they are inexperienced. Prats speeding in build up areas are the real issue!

[/Parent mode ]

TonyG

There was an interesting demo of stopping distances on Driven last week. They were testing a re-vamped Jag E-type which had a lot of new modern technology and campared it ot an original Jag E-type. Braking from 70 mph, the old E-type stopped withing the distance specified in the Highway Code, but the one with all the new technology stopped well within the distance, and I'm sure it was 3 or 4 car-lengths further away from the line of cones.

NBW

Firstly, as has been pointed out the braking distances in the Highway Code are about thirty years old.

For example, the Highway Code quote stopping distance from 30mph as 23 metres, 9 metres reaction and 14 metres braking distance. WhatCar? quotes just under 10 metres braking distance for a WRX and 11.6 metres for a Ford Ka.

Secondly some people seem to think that because their car has excellent brakes it means that they are safe to drive at at least 30mph down this narrow street with cars parked each side, but drivers of lesser cars are not. Bo11ocks! Even 30mph may not be safe at all.

In the situation where a child runs straight out in front of you reaction time is going to be more critical than a short stopping distance. The difference between being hit be a driver braking from, say 20mph, and being hit by a driver braking from 30mph NO MATTER HOW GOOD THE BRAKES could be life or death for the child.

The driver doing 20 mph will travel 6 metres in his reaction time, the driver who was doing 30 will have travelled a further 3 metres BEFORE applying the brakes.

Just my thoughts....
Tim



[Edited by NBW - 2/18/2002 10:46:01 PM]

boomer

Scooby_Maxus

[deja-vu quote]So let me get this straight, your child pours a pan of boiling water over their head in the kitchen, kills the child and it’s the parents fault!

What a pile of..............

If only the electricity/gas/water company had been driving, er, heating the water to 30 degrees, then everything would be fluffy bunnies!

I guess that utility companies never had kids? Right?
[deja-vu quote]

ANYWAY - i will now drive at EXACTLY 30mph, in built up areas, past schools, at going home time, without looking where i am going - knowing that nobody will be in the slightest bit hurt. Isn't science wonderful

mb

NBW

LOL @ Boomer

Yep, everyone knows it's safe to drive at the speed limit, because only speeding people have accidents - The Government tell us, so it must be true......

Tim

father_jack

My 2p - the advert shows a crap car locking up for ages then hitting a ped.
Regardless of it being a **** car - this ad should have a sequel.

The driver realises he's locked up - lets off the brakes and steers out of the hazazrd. No one is hurt....
Sorry that's far too sensible - it'll never happen.

tiggers

Scooby_Maxus,

Prats speeding in built up areas are NOT the real or only issue.

The real issue is society. Britain is becoming a society where certain sections of it are becoming victimised while the rest go unchecked. One of the emerging features of this society is that kids can do no wrong.

In such accidents it's not always the drivers fault and of course it's not always the parents/child's fault, but what I am saying is that for some reason a lot of parents don't seem to want to or even feel a need to educate their offsping about such basic things as crossing the road. Then as soon as their little darlings get hit by a car they automatically blame the driver REGARDLESS of the speed he/she was doing.

tiggers.

BigJon

Being in the driver training industry I have to agree that the commercial mentioned does not convey the message very well, the theoretical situation below is, IMO, a better way to highlight the problem.

Two identical cars are travelling along a dual carriageway. For this calculation I am assuming that both drivers will react in the same time.

Car A: Driving in left hand lane at 30mph.
Car B: Driving in right hand lane at 40mph, about to pass car A.

As the cars are level a mother with pushchair walks into the left hand lane ahead of them, the mother trips and is now lying in the left hand lane but the pushchair has rolled into the right hand lane. It’s one hell of a coincidence I know but this is only to highlight the relationship to speed and stopping.

Both drivers (assuming the same reaction time) initiate a full emergency stop (abs operational).

As car A stops (2cm before hitting the mother) car B will still be travelling at 26mph.

The mother, still lying in the left hand lane, will obviously be very upset because her child has just been hit by a fairly solid object weighing in excess of 1000kg at 26mph.

Speed is only ever a contributory factor. Please remember that, as the speed increases, braking distance increases exponentially.

It is easy to get speed but much harder to get rid of it.

FreeT

Very true but you could be a very cautios driver, carefully driving along at 10mph between tighly spaced cars and a kid runs out from behind a van and still kill them in an unfortunate contact or under wheels. The only way to reduce accidents in these built up areas is to reduce speed and increase awareness. Kids are kids after all and its very easy to get distracted and forget where they are. Drive sensibly and you will reduce chance of an incident. God i'm boring myself now, c ya.

TRIGGER

This last post is a good point - but also goes to dismiss alot of what has been said, in reference to the advert. It isnt the difference between hitting somebody at 35 as against 30 - it is whether you hit them or dont. The actual final impact speed in this scenario would be quite slow.

Overall I think the advert is rubbish. My wife went on a driver training day a year or so ago and the instructor insisted that all cars brake at the same rate, after she had comments that our Scooby was going to outbrake most cars. She wasnt convinced so asked my opinion. I assured her that different cars braked at very different rates. Coincidentally Clarksons piece about braking distances was on the next week - she was then convinced. The Porsche outbraked the Discovery by miles, let alone the Anglia !!

Anyway, in my opinion there are so many mixed messages and rubbish spouted, that these adverts, which should be a good thing, get ignored most people. Driver training and education is the main thing - you spend months training people to drive slowly around town, and then let them do 70 mph on motorways with no training at all !!!

Tiggs

ITS AN ADVERT ON TELLY

most people do not have cars that they are interested in, most dont have subarus and most dont know what they are- shocking im sure.

the advert is designed to get adults to think about their speed in 30mph limits.

its not for kids, if you want kids lessons then go to a school- dont watch TV at 9pm and moan that the advert isnt telling 5 year olds what to do.

and as for the "ohhh, rear brakes havent locked" "he should have steered round it" "he should have switched to noitrous and whizzed passed before thekid got there"..... this is an add on the telly. Do you think there are people out there who moan about the chewing gum add where the bloke gives it to his lawn sucker "ohhh, a lawn sucker could never go that fast"

its on the telly, its not a physics lesson- its meant to make joe bloggs think.

Tiggs

ps i was just reading a web site on movie errors, some were funny but when i got to the Top Gun stuff it was full of stuff pilots had sent in about how Maveric couldnt possibly do a neg G dive while inverted on his Mig38 while tied to a Goose" etc- just made me think- how sad that these guys prob hated the film cause in their eyes it was so inaccurate. How do you lot get through a day????????? theres sooooo many cars around on tv all doing things they couldnt possibly!

stephen30

I agree with that. Has anyone seen the Punto ad where the car is moving and the brake lights are on!

Steve

Tiggs

what about the add where the blokes in a van ask the girl for directions and she gos on about "at the next right, drop her into 2nd, may need the traction control, go through a series of demanding s bends....."

just imagine some of you "yeah, liked you really drop into 2nd without blipping the throttle, blah, blah, blah"

Tiggs

juan

spot on Tiggs,

and Robertio. Your reaction time thoughts are wide of the mark. Your reaction time is the amount of time it takes to register that there is a problem then brake surely.
But you already know there is going to be a 'problem' and probably even have your foot hovering over the brake pedal as you approach your lamppost.

Diablo

My thoughts:-

1) The add is pants and totally misleading. Typical goverment dross.

2) 90% of license holders should NOT be allowed on the roads because they are a: thick and b: incompetent

3) Parents MUST take responsibility for their kids actions and stop spouting this pi$h about "kids will be kids". For God's sake, if the kids cannot be trusted to know about the dangers of vehicles then what the bloody hell are they doing out unsupervised and playing in the streets anyway?????

From as young as I can remember I was tought the importance of road safety and never came close to running accross a road without looking first

Sorry, but in the tragic event that I hit someone in an unavoidable situation where I cannot reasonably be to blame (aside from getting out of bed that day ) I am not going to spend the rest of my life wallowing in guilt beacause some dumb parent cannot look after their children properly.

If I let my soft lump of a well trained Rottweiler off her lead under supervision I get horrendous looks from parents who will happily send their young kids off to primary school across busy roads unsupervised

Am I the irrisponsible one? I don't think so!!

D

Tiggs

well thats ok then

Diablo

Er..no,

Cos it doesn't change anything

Just my thoughts as I said

D