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I second that! People have started creeping out of lights and doing 5mph under the stated limit on country lanes near where I work.
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Another study which was done this week shows only 7% of the UK's commuters use the bus. And another 9% use the train i think it was, and most of that is probably London. And the public transport system cannot cope with that, so to encourage more people to use it is a really bad idea. If everybody jumped on it today, it'd grind to a halt and take a month to get where you're going.
Theres 8 million more vehicles (roughly) on the road now than there was 15 years ago, our roads were never built to handle that, and poor road building schemes, motorway widening plans etc all being shelved due to no money, and sky high fuel prices is leading people to drive slower also, slower acceleration, meaning where 5 cars used to get across the lights its now 3, it all adds up.
A funny thing is, i used to do traffic survey's for the council about 7 years ago and it used to strike me that people who live in one place, drive to work in another, and vice versa. Why not just swap jobs/houses with people in the other direction and save all the hassle? LOL!
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The creeping away from traffic lights is the worst. It doesn't even save fuel-it simply stops the instant mpg reading going into single figures momentarily. Some people shouldn't be given data because they'll only misinterpret it!
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True, what helps mpg is not stopping when not required (reading lights ahead etc, normal stuff i was even taught on normal lessons) and maintaining a steady average speed. ie not haring up to things, slamming on the brakes and haring away from it. If you've stopped at the lights then you've already stopped, creeping away from them isnt going to change anything.
But the advice is misleading, and people are told to "accelerate slowly" and to keep low revs etc, so it ends up with people taking four hours to get across traffic lights.
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Well how have people come up with these new habits? I learnt to drive in 2008 and my instructor taught me to keep it rolling if possible, keep my foot steady on the gas, don't use the brakes unless you have to stop properly, come out of gear at lights etc, and set off promptly so as not to annoy other road users. Yet I see people who must have been driving 15 or 20 years more than me crawling out of lights and slamming on at the slightest hint that the queue ahead is slowing.
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I passed my test in 2002 and my instructor taught me to use the gears to slow the car down, ive spoken to someone who is doing lessons now and her instructor isnt teaching her that, which i find...interesting. I think with alot of people driving for years they get lazy and develop a habit which i have a tendancy to do now that i drive an automatic which is to always half-hover over the brake and tap it without realising it. I was doing it for some time until i was the lead car for a trip somewhere and my friend driving the car behind told me my brake lights kept coming on for no reason and then i realised i was doing it again and have recently been trying very hard to stop doing that.
Also alot of people with manuals will sit in gear at the lights riding the clutch ready to shoot off, i must admit i did the procedure of handbrake on and out of gear for about three weeks after my test then developed my own method LOL!
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Nooo always put the handbrake on at lights, in queues etc. If only so that if some knob rear-ends you, you were properly stationary and less likely to rear-end whoever is in front of YOU!
The brake light thing is naughty. I hate that on the motorway especially.
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Yes i know the reason why you should use the handbrake, now i drive an automatic i just sit there with it in D and my foot on the brake and let my foot off and obviously it moves by itself.
I'll own up to not doing it properly when i drove a manual but in my defence theres very little point in using the handbrake in my 406 Executive because it doesnt work. But with it being an auto it doesnt matter. I know i should put it in park but i just....dont LOL.
But yes ive been told ive developed that very annoying habit of tapping the brake without realising it, especially on the motorway, as far as im aware i never used to do it when i drove a manual but like i say it wasnt until recently somebody told me i was doing it, im focusing very hard at the moment to make sure i dont do it, ive always been a semi-nervous driver, i dont know if that has anything to do with it.
Edited by jamie745 on 03/06/2011 at 21:12
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I always use the handbrake when stopped for more than about two seconds. I got fed up with cars with really bright brake lights sitting at traffic lights for ages-and realised that I was one of them! It can be quite dazzling if you've been driving in the dark.
As a new driver I used to keep it in first (frightened of not finding the gate when the lights changed), but you're not meant to keep the clutch pedal pushed in for extended periods of time. Apparently it wears the throw out bearing. You get smoother starts with the hand brake too because there's no fear of rolling backwards. I think only Americans neglect to use the 'E-brake' (ugh!)-it's a really underrated tool.
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Well as i said earlier, no point in using it in mine as it doesnt work (seriously, i drove 16 miles with it on before i realised it was on) and its passed four MOT's despite that so im not complaining. Obviously i should put it in P instead.
Im still waiting for you to have a go about my tapping the brake tendancy LOL.
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I would never adminish a driver for alerting other drivers to his incompetence...
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You have this way of both insulting and complimenting someone in one sentance.
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Hmm, those of us brought up on BMC vehicles with graphite clutch release bearings[1] learned very rapidly that the clutch should only be touched when changing gear. As quickly as practicable. That made the difference between 30,000 mile clutch changes and 10,000 mile clutch changes.
On the other paw, I lived in CZ for a while. For some reason (I'm betting on generations of Soviet-Bloc vehicles prone to handbrakes freezing on, coupled with serious winters) they never touch the handbrake under any circumstances. When queuing on a hill, the state of the front end of your car is entirely dependant on the "heel and toe" skills of the driver in front of you. Local insurance claim rules work under the assumption that if you were rolled back into, you were too close. I once perfomed a smart handbrake hill-start with a local colleague in the car. He was astonished and insisted that I did it a few more times to show him how it was done.
[1] Nominally "self adjusting", actually "wear out very quickly".
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Brakes are for slowing down not gears the modern day engine has such a light crankhaft that its effect on braking the car is neglibable.your driving intructor is living in the past.
Find a steep hill travel down wihout throttle in different gears you have to be in first or second to have any real effect.One of the reasons for changing down is that it makes accelerating easier .
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light crankhaft that its effect on braking the car is neglibable
The weight of the crank has no effect on engine braking. The braking effect comes from the friction of the pistons, and in petrols, the pumping losses past the throttle.
It's useful on long descents-otherwise it is an anachronism.
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Engine braking is caused by the partial vacuum in the cylinders that happens if you restrict the intake, and the pressure on the other side of the cylinder pushes on the remaining fluid. The force thus opposes the momentum of the vehicle (via the transmission). The crankshaft merely surrounds this and doesn't contribute. Diesels should be better at it than petrols.
This is my physicist answer so sorry engineers who have a more techy explanation!
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Am i the only one who finds a woman giving a technical mechanical answer about a car to be incredibly sexy?
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Bobbin-you've blown it!
There's no/little throttling on diesels therefore the intake stroke is thermodynamically reversible. The compression stroke and subsequent expansion stroke are also reversible. Since there is no combustion, the pressure at the end of the expansion stroke is atmospheric so no pumping loss on the exhaust either.
Engine braking on a diesel is purely due to friction-mainly from the rings. The Frictional BMEP is higher for a diesel than a petrol because the compression ratio is higher-but there is assistance from pumping losses. Overall, petrols provide more retarding force.
For this reason commercial diesels in the US/Australia are often equipped with a 'jake brake' which opens the exhaust valve at the top of the compression stroke thus dissipating the considerable work done by compression. Fantastic braking capability but rather noisy-especially without a muffler.
(Jamie's dreams are shattered)
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Never driven a diesel. You mean a compression brake? I thought diesels did have a way of engine braking; you don't get intake throttle, you get exhaust throttle instead. The work is done using fuel flow instead of gas flow. Am I right? So diesels ought to be better as I think that would produce more inverse torque. Or....petrols rev higher so that might make them better at it. I can't decide now damn you!
I did apologise to engineers! This was a physics guestimate!
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Arrgh! Even your point mass on an inextensible string-sliding over a frictionless mass less pulley-contained with a vacuum Physics is wrong!
A jake brake is a compression brake. But the compression stroke does NOT in itself provide any net braking force since the work done during compression is returned during expansion even in the absence of combustion. A compression brake works by dissipating the work done on the compression stroke by opening the exhaust valve at the top of the compression stroke.
Some commercial diesels are fitted with an exhaust throttle-which DOES provide pumping losses-and a net braking force. But they are obviously not as effective as compression brakes.
Diesel cars are fitted with neither-the service brakes are considered sufficient for most braking duty (which answers the earlier point about engine braking).
The work is done using fuel flow instead of gas flow
Diesels regulate output via fuel 'throttling', whereas petrols regulate output by airflow and keep the air fuel ratio virtually constant. Fuel flow is shut off during overrun-and hence isn't relevant.
Edited by unthrottled on 04/06/2011 at 23:51
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Your point about petrols revving higher is relevant-assuming the revs are being used. Automotive engineers work in terms of BMEP (Brake Mean Effective pressure). since this is independant of engine size and RPM.
Total braking work = frictional MEP+pumping MEP
Diesel : Fbrake = ~1.25 bar+~0.bar=1.25bar
Petrol: Fbrake = ~1 bar+0.75 bar=1.75bar
Braking power =Fbrake*RPM*constant
So, yes revs matter!
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Adiabatic expansion of the squashed gas = no energy to crankshaft but the engine is still turning over = net energy loss = diesel engine braking-like effect. Yes?
What happens with turbodiesels? Surely they will add to the effect.
I know how petrols work :-P
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Finally you have put some formulae in. It's about time!
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1.)Yes!
The turbo doesn't really have much effect on engine braking at all since it is not connected to the crank. It does provide a restriction to exhaust flow-but that is partially compensated for by the increase in intake pressue. The pumping work done by the piston is the difference between the pressure of the exhaust and the pressure of the intake.
In all honesty there is not enough enthalpy/pressurein the 'exhaust' gas during overun to provide much restriction to theexhaust or boost-so the point is moot!
P.S I'm currently in another entangled discussion about the merits (or lack therof) of nuclear power. The numpty keeps banging on about TMI/Besse-Davis and refuses to see the bigger picture. :(
Edited by unthrottled on 05/06/2011 at 00:28
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It is a limit - not a target >):
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Too technical for you Jamie? Faint heart never won fair maiden...
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Its so technical that its not even sort of interesting.
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Sorry unthrottled, I don't think Jamie finds it quite so sexy when you do it.....LOL
I've got a PhD in quantum physics though ;-)
If you want back-up on the nuclear power thing, gimme a shout because that's my industry. Davis-Besse is American and that's all you need to know about their safety record. Sellafield is run by Yanks too and their attitude is cavalier to say the least.
Thanks for the diesel clarification dude.
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No probs! The pumping loss thing can be like a magic eye.
I used to try to argue that the pumping loss was the difference between the crank case and the intake because it was easier to visualise the gas forces acting on each side of the piston. Then I realised that the volume of the crankcase doesn't change (as one piston goes down, another goes up so dV=0, so PdV=0).
Quantum physics drove me into engineering!
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OTOH I think i might put a single dimensional Schrodinger Equation signature into my posts-just to upset Jamie!
I thought Sellafield was owned by BNFL?
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You want the full Navier-Stokes ;-)
Sellafield is owned by Nuclear Management Partners and the head honcho is a Yankee. BNFL doesn't actually exist anymore.
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Sorry Bobbin even with you its gone beyond sexy and into mind numbingly boring. Ive understood approximatley three words of the last 4 posts.
I think its time you two get a room.
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My brain stopped listening at PhD. The next paragraph may aswell of been in Hindi.
You may think you're all special with having a PhD in...whatever it was. But ive got a purple star on Ebay. So there!
Edited by jamie745 on 05/06/2011 at 18:51
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Oooooh toys thrown well out the pram eh lad...?
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I just dont see how a thread about congestion got reduced to the most boring discussion on the face of the earth about...particles and...stuff!
Your PhD still cant beat my Star! :P
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Jamie...in the beginning, there was the Big Bang....
Come on unthrottled, what's next? ;-)
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I'll give you a big bang if you keep being cheeky.
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Ooh! Neutron irradiation induced embrittlement of low alloy RPV steels? That was my topic 'back in the day' when I was a budding physicist. Bit of light popular science for a Sunday evening?
Or if you fancy something more automotive based: how about the competition between gas and inertial forces acting uponn a recipricating assembly and the impact upon NVH. This is one of my favourites since the latter is often confused with the former in the popular literature (auto Express et al.)?
Thoughts Jamie? ;)
Edited by unthrottled on 05/06/2011 at 21:33
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Awesome. You published on it?
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I worked on the 'little' PWRs. We didn't publish an awful lot! ;) Everything was classified-even the canteen prices.
tbh it wasn't my cup of tea and I jumped industries.
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I've got ten more days in it - it's not that I haven't enjoyed it but I've got other ideas about work that I like better. Plus the nuclear industry is incredibly slow.
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The galacial rate of change drove me nuts. I had this haunting fear that I would be doing the same dull safety case a tthe end of my career as at the star!
What are you moving on to?
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Me too. Some clients are very prescriptive (you can guess which - the massive one in Cumbria!) so you're forced to put what they want.
Do not laugh but I am training to be a physics teacher.
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So you can convince impressionable young minds that a career in physics is really cool 'cus you get to hang out with Brian Cox in CERN?!?! If I met my Physics teacher, I'd give him a piece of my mind!
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I absolutely cannot stand Brian Cox. He is a p****** -I have met him. It takes him on average 18 seconds after meeting you to tell you he was in D-ream. He can empty a coffee room quite quickly!
I'm hoping to teach in college and work my way back to academia.
I already taught undergrads during my PhD and I made some of them cry with my homework critique so hopefully I will like teaching 6th Formers better.
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Ummm....great!!! Or...bad!! Or...whatever.
Seriously i didnt understand any of that.
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What don't you understand about being a physics teacher, Jamie? I'm a classics graduate but even I understand what physics teachers do. I suffered one for a year at school before giving up science and concentrating, thankfully, on classics.
But I know it takes courage so the very best of luck, Bobbin. I quite often interview people (for an accountancy firm) who are coming out of teaching, either through endless changes to the curriculum or through bolshie teenagers, or both.
And I'm the first to admit that a lot of the things we take for granted in the modern world are owed to physicists - including the development of motor cars....and here we are back where we came in - Congestion.
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Avant i dont even know what "classics graduate" is, my guess would be something to do with music but i never went to college, or university, i never did any A levels, my attendance record at school was underwhelming to say the least and when i was there i didnt pay much attention, to say i dont know alot about the education system or what the fancy terms mean would be an understatement.
Ive never had any interest in anything like physics or science as i find it incredibly boring and wouldnt have a clue of what goes into being a teacher of such a dull subject. But despite a lack of knowledge on anything education related i think ive done reasonably well for myself considering, proving you dont need fancy degrees, middle class upbringing and letters after your name.
By the way, is classics anything to do with music? Just curious.
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I am married to an excellent ( as in awarded by the IoP for being such) Ex Physics teacher who was absolutly passionate about her subject, she only taught "A" Level as she reckoned she would have frightened the wee ones.
It is quite lovely to see how her Ex pupils greet her in the street, even the ones she would have described as "scamps".
btw D..... commented that most of the brighter ( & she did not reckon herself to be among them) Physics graduates went to work in the "City" where their formidible mathethmatical /analylitical ( my spelling is terrible) talents were appreciated if perhaps in hindsight misused.
I believe Rutherford said "There is only Physics.......the rest is merely stamp collecting" or words to that effect.
Cheers
All
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Jamie - no indeed, you don't need letters after your name at all to do well in life. I just love learning! I'm not from any middle class background either (I'm a Scouser for a start!) and hard work and an enjoyment of my subject got me to where I am.
Yeah dieseldogg - they do try to get you to do finance! All of us with Firsts were herded into a room at uni and given us a presentation about being actuaries and city bankers. I just am not interested in money and certainly wouldn't want to live in London so it never piqued my interest.
I think I might frighten the little'uns. I've got to do a primary placement before I start my course and I cannot stand kids! They've got to get to 14 or so.
Rutherford did indeed say that - it apparently irked him till he died that he got his Nobel in Chemistry and not Physics!
Obviously, I'm basically just working so I can have cars :-))
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It could have been worse, much worse
It could have been..........................................................biology
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Biology is much worse!! Agreed!
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I think Bobbin should get her own science forum.
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Oi grumpypants, leave me be! I don't care if it goes off topic on threads I start!
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