I agree that the hypothetical motorbike rider is at fault but I posed this question as an example to illustrate the danger of the 3-2-1 manouver.( I don't ride a bike incidently). If the overtaking 3-2-1 driver had only completed a 3-2 overtake then he would have seen the motorbike before he had started the 2-1 move.With the level of traffic today each driver must drive defensively not only for his life but for other peoples lives as well .You have to assume some people will do wrong things because theyr'e not concentrating or aware of their surroundings ( or they are idiots, but even idiots don't deserve to die) .

Might not have been clear in Crab's post, but the 3-2-1 manouevre is still treated as 2 manouevres (ie 3->2 and then 2->1) even if the plan is to do them in sequence. So, if something changes upon arriving in lane 2, the plan would have to change to reflect that, rather than just flying across 3 lanes regardless

Chris

Might not have been clear in Crab's post, but the 3-2-1 manouevre is still treated as 2 manouevres (ie 3->2 and then 2->1) even if the plan is to do them in sequence. So, if something changes upon arriving in lane 2, the plan would have to change to reflect that, rather than just flying across 3 lanes regardless

Chris

I know I said I was gogin but ScoobChris has restored my sanity! Thanks, you've hit the nail on the head and I appreciate that!

1. Do you think people in lane 2 are surprised by people overtaking in lane 3? I would think they'd be more alarmed if they were being help up in lane 2 and were looking to use lane 3 and someone "suddenly" appeared. One of the keys to minimising the surprise element might be to move into lane 3 earlier so that you don't get lost between their mirrors as you close on them. This will also give you a better view ahead of the situation ahead of them to see whether they're likely to move out before you commit to the overtake.

2. Completely agree about drivers being unpredictable. However, does driving past them slowly make the situation any safer once you're past the point of committing? Surely once you've committed, you want to be past as quick as possible? So the key is making sure you have their reaction *before* you get to the point of committing. Again, if you get into lane 3 earlier (without changing speed) you have more time to generate a reaction before you commit to the overtake.

Ah the great signalling debate It's a shame that you dropped it because of that as I think it's a very minor part of the course and I've spoken to examiners who expect you to always signal and those who expect you to signal "if it is of benefit to someone you can see or you can reasonably expect someone to appear who will benefit from it". That sums it up for me Perhaps a better question to ask is "is there a good reason for me NOT to signal?" and scenarios where this might apply is where it could confuse or mislead other road users and this is far more important imho. Perhaps another case of asking for a more open-minded observer

Chris

I agree on both point 1 and 2, but I still believe if your entry speed is nearer it will give the lane 2 driver more time to see and react to you before the actual overtaking happens. I check my rear view mirror fairly frequently, I would say nearly 60-40 (maybe 70-30) split on vision. yet I still find it difficult to anticipate the speed of the oncoming car (from behind) to get out the way if they do a tonne without a hint of slowing down... If I find it hard im sure less active drivers will really struggle to see you until your right next to them.

I dunno, its quite hard to explain, overtaking or being overtaken at high difference of speeds feels more risky imo, maybe I've not had enough experience to fully understand yet..

Yeah about the IAM I did ask, the same question in much less words. I simply said "Why not?", then he gave me a lecture that if your not 100% sure you shouldn't of went off..

I know I said I was gogin but ScoobChris has restored my sanity! Thanks, you've hit the nail on the head and I appreciate that!

If your skills in writing matched my skills on the road (yours arguably should be higher) I suspect this thread would be 2 pages shorter. I think I agree with you (following Chris's disambiguation) in principle now, provided the traffic is light enough that I can see a "landing zone" some 200 yards long in lane 2 and lane 1.

If your skills in writing matched my skills on the road (yours arguably should be higher) I suspect this thread would be 2 pages shorter. I think I agree with you (following Chris's disambiguation) in principle now, provided the traffic is light enough that I can see a "landing zone" some 200 yards long in lane 2 and lane 1.

I thank you! As Chris said, it's hard to get something in words which I could show you so easily. It's a pity we can't wave our arms around a a forum, that'd help!!

I thank you! As Chris said, it's hard to get something in words which I could show you so easily. It's a pity we can't wave our arms around a a forum, that'd help!!

Oh yeah; I should add that I'd describe myself as an acceptable standard driver with above average car control, not as a good driver!

Is this strictly true? Imho, maintaining a constant speed is not ideal for economy especially where the road is not 100% level.

My understanding is that maintaining a constant speed is ideal for economy because drag does not increase linearly with speed.

For the sake of simplicity, let's assume that if we speed up by x mph down hills, we will slow down by a similar amount up hills, such that the whole journey's average speed (and hence journey time) remain unchanged. The actual effect of the hill itself can be ignored, because the energy (work) required to lift an object is equal to the energy it will release when it descends. What we are left with, then, is a journey consisting of a few periods of increased speed and a few periods of decreased speed. However, since doubling the speed will increase drag by a factor of 8, the small increases in speed will require a pretty huge increase in effort, which will not be fully recouped by a corresponding small decrease in speed.

Now all of this is very theoretical and pretty far removed from the real life effects of friction, and so on. I also haven't studied maths at this level for quite a few years and am liable to have made one or more fundamental gaffes - please feel free to set me straight!

EDIT: Apologies for digging up an old thread. Hadn't realised how old it was.

Edited 2 December, 201015 yr by will_

My understanding is that maintaining a constant speed is ideal for economy because drag does not increase linearly with speed.

For the sake of simplicity, let's assume that if we speed up by x mph down hills, we will slow down by a similar amount up hills, such that the whole journey's average speed (and hence journey time) remain unchanged. The actual effect of the hill itself can be ignored, because the energy (work) required to lift an object is equal to the energy it will release when it descends. What we are left with, then, is a journey consisting of a few periods of increased speed and a few periods of decreased speed. However, since doubling the speed will increase drag by a factor of 8, the small increases in speed will require a pretty huge increase in effort, which will not be fully recouped by a corresponding small decrease in speed.

Now all of this is very theoretical and pretty far removed from the real life effects of friction, and so on. I also haven't studied maths at this level for quite a few years and am liable to have made one or more fundamental gaffes - please feel free to set me straight!

EDIT: Apologies for digging up an old thread. Hadn't realised how old it was.

Not necessarily; if the downhill is steep enough that you gain speed on a constant or reduced throttle, you are not using more fuel for unit distance than you would at constant speed on a flat road.

Oh oh I think I can answer this the best way to save fuel is not to keep at consistent speed, although it does have a part to play.

optimum speed for level ground is e.g 50mph.

optimum for inclines and declines are different however! if coming up to an incline one should speed up prior to incline to increase speed, as bearing load on engine at level ground is better than bearing load when it is at an incline, so its a fine balance between;

~ how much speed increase before incline and

~ the intense/duration of incline itself.

Obviously the speed will decrease as you climb as your trying to put minimum load possible while incline, this also needs to be a fine balance between;

~ speed decrease and

~ increase in load for acceleration.

The second thing to note is that if you are reaching brow of incline you should release load bearing sooner so you will either

(A) minimise load bearing time on incline or

(B ) let the force of gravity pick up your speed again if you are going down hill after.

This is normal practice for truckers (or supposed to be if they want high mpg) along with optimum gear ratios etc.

Edited 5 January, 201115 yr by JLneonhug

I'm an advanced driver - same qualifications as Crabs25.

My advice for motorway driving is this:-

1. Keep a steady distance between you and the vehicle in front. Make sure that you will have plenty of time to react should the worst happen ahead.

2. Stick to the speed limit for that road. It's the law of the land and is there for a purpose - to protect life and reduce the number of KSI's (Killed or Serous Injury RTC's). I know that some people would argue that cars now are more than capable of stopping from high speed quicker than the the Highway Code states and that the speed limit should be increased (or as I've seen from some in this thread - ignored). It is not the car but the driver than needs to be taken into account. While I agree that some may be able to drive at high speed you MUST take into consideration the skills and experience of the other road users and any other issues that you might come across- i.e. a tyre blowout, debris on an unlit section, a car crashed in your lane which you cannot see at night (believe me, that DOES happen and I've dealt with the results of one such) - all sorts of issues. Drive above the speed limit and get points. Drive above 100mph and face a ban and all the insurance costing implications that involves - or worse still - kill or injure someone due to excessive speed and face upto 14 years in prison for S1 RTA 1988 - causing death by dangerous driving.

3. Observe lane discipline - as has been said before, Lane 1 is the main lane and the others are for overtaking only.

4. Try to avoid harsh braking (see point 1). We all get stuck in long tail backs only to find nothing at the head. Well, most of this is caused by lack of distance and braking, this causes a concertina effect further back which after a few miles means stationary traffic and frustrated drivers - so easy to avoid by keeping distance and watching ahead! The motorway backs up at a rate on 1 mile per minute at busy times (more on the M6 or the M25!

5. Keep relaxed - despite what others say there is nothing wrong with being relaxed while driving. However, you MUST stay alert. If you find your alertness drifting then concentrate, if that becomes hard then stop at the next services and take a break - don't become like some posters and drive like a madman to keep alert, you're asking for a ticket or a crash that way.

6. Slow down in reduced visibility. Today I drove back from the Lake District and the view distance was reduced by spray to about 100m and so I reduced my speed - I got in a nice space between a line of trucks out of the spray and I set my cruise to match theirs - no braking was needed (unlike the fools passing at high speed) and I was out of the worst of the spray. I saw a large number of idiots pass me at speeds I would estimate to be 90 to 100mph (and yes, I am an expert at judging speed).

7. Give foreign registered HGV's a really wide berth. Pass in lane 3 if safe and you're not going to hold up drivers already in that lane. If lane 3 is not available then WAIT to pass until you have a clear run through - accelerate past (within the speed limit) in one fluid movement. DO NOT SIT ALONG SIDE IF AT ALL POSSIBLE, doing this is asking for trouble and the number of 'Blind Spot' RTC's is on the increase.

8. If possible give yourself an escape route. What I mean by this is be aware of your surroundings and try to drive staggered from the vehicles around you. That way if you need to you can change lanes to avoid a collision. This is not always possible or practical (in heavy stationary traffic or when passing in lane 3) but it's a good thing to be aware of - especially when passing 'heavies'.

9. Do not undertake unless the lane to your right is slowing and yours is not. The Highway Code allows for this as some have already noted - but it does not allow for lane changes to undertake a few cars that are driving slower in your lane. You MUST wait for them to clear you lane and then OVERTAKE. That type of undertake is extremely dangerous and one I NEVER do - and believe me there have been times when I've really needed to get somewhere fast on the motorway but have been held up for several miles - but I have not undertaken as I want to go home without broken bones or a death on my conscience.

Most of all, stay safe and drive responsibly. Fuel or speed should not be your first consideration - safety is always paramount when driving anywhere, but especially so when driving on the motorway.

Rich

4. Try to avoid harsh braking (see point 1). We all get stuck in long tail backs only to find nothing at the head. Well, most of this is caused by lack of distance and braking, this causes a concertina effect further back which after a few miles means stationary traffic and frustrated drivers - so easy to avoid by keeping distance and watching ahead! The motorway backs up at a rate on 1 mile per minute at busy times (more on the M6 or the M25!

I've seen CCTV footage of a "standing wave" (correct name for this phenomonon) backing up faster than a Police class 1 driver could reverse a RangeRover.

I have a query which is kind of related to motorway driving..

The question is - What is the most optimal for increasing in speed to reach optimal speed?

So e.g. will it be more fuel efficient if: from 30mph if I took 40 seconds to increase speed to 50-60mph, or will it be more fuel efficient if I only took 5 seconds? Because I am in the optimal speed for longer.

What is the most optimal for increasing in speed to reach optimal speed? So e.g. will it be more fuel efficient if: from 30mph if I took 40 seconds to increase speed to 50-60mph, or will it be more fuel efficient if I only took 5 seconds? Because I am in the optimal speed for longer.

Like my previous reply, this is pretty theoretical, ignores lots of real-life factors, and tends to concentrate on the extremes.

Ignoring the need to plan ahead (for hills and the like, as already discussed), the optimal speed is the slowest speed you can do in the highest gear you can use. This is because lower gears spin the engine faster, reducing efficiency by increasing frictional losses, and higher road speeds cause increased drag, which increases non-linearly (with the cube of the speed). Most of the time this will place you in top gear but on steep uphills or wiggly roads, it may be a lower gear.

One aspect of your question therefore becomes: Is it better to stay in a low gear in order to accelerate faster, or change up as early as possible at the expense of acceleration? Higher gears are better for economy so the best option would be to change up as early as possible but sacrifice the ability to accelerate quickly. This suggests slow acceleration is better.

What remains unanswered, though (and what I suspect your question is more about) is best illustrated by example. Suppose you were accelerating up to 35mph (not uncommonly the lowest speed that can be comfortably sustained in fifth gear, notwithstanding gradients). Starting in first, you'd change up to second as soon as possible and remain in second until you were able to change up to third, and so on. If you were to change up in this manor, you'd have to apply a fair bit of power when you first changed up but accelerating up to the next gear change, you'd have the option of reducing the power. For instance, during the time when you were in second gear, should you floor it (in order to reach third more quickly) or gradually reduce the power such that third is "only just" reached?

I don't know the answer to this. My gut instinct is that you should apply the maximum power within each gear until you are able to change up. However, this opinion is only based on the loose notion that at the other extreme (accelerating "as gently as possible") you'd never reach the next gear. I'm sure there are plenty of "common sense" solutions but does anybody have a mathematical explanation?

I've seen CCTV footage of a "standing wave" (correct name for this phenomonon) backing up faster than a Police class 1 driver could reverse a RangeRover.

It's only called a standing wave if it remains stationary (relative to the road). This can happen if the wave is travelling back through the traffic at the same speed as the traffic is moving forwards, or - as Ken points out - it can travel back faster than the traffic is moving forwards.

I have a query which is kind of related to motorway driving..

The question is - What is the most optimal for increasing in speed to reach optimal speed?

So e.g. will it be more fuel efficient if: from 30mph if I took 40 seconds to increase speed to 50-60mph, or will it be more fuel efficient if I only took 5 seconds? Because I am in the optimal speed for longer.

VAG actually did a study on this for diesels some years back (sorry no weblink), and the answer may surprise you. Provided you maintain constant upshift revs, it is equally fuel efficient to accelerate hard as to accelerate gently.

It's only called a standing wave if it remains stationary (relative to the road). This can happen if the wave is travelling back through the traffic at the same speed as the traffic is moving forwards, or - as Ken points out - it can travel back faster than the traffic is moving forwards.

To clarify, AIUI the "standing wave" effect relates to the "downcarriageway" (aka front) end of the jam remaining at a more or less fixed point. The speed of movement of the rear end upcarriageway is a function of the traffic density on the road.

What remains unanswered, though (and what I suspect your question is more about) is best illustrated by example. Suppose you were accelerating up to 35mph (not uncommonly the lowest speed that can be comfortably sustained in fifth gear, notwithstanding gradients). Starting in first, you'd change up to second as soon as possible and remain in second until you were able to change up to third, and so on. If you were to change up in this manor, you'd have to apply a fair bit of power when you first changed up but accelerating up to the next gear change, you'd have the option of reducing the power. For instance, during the time when you were in second gear, should you floor it (in order to reach third more quickly) or gradually reduce the power such that third is "only just" reached?

I don't know the answer to this. My gut instinct is that you should apply the maximum power within each gear until you are able to change up. However, this opinion is only based on the loose notion that at the other extreme (accelerating "as gently as possible") you'd never reach the next gear. I'm sure there are plenty of "common sense" solutions but does anybody have a mathematical explanation?

At 33-35mph I'd probably hang on 4th on the fabia (at ~1.5k), rarely would go to 5th due to low rpm ~1k.

Anyway the way I've been taught was to box shift upwards (2nd -> 4th etc) to be more economical, of course this will imply using more of the rev range at lower gears. So, one wouldn't really want to hang on high rpm for a long time if they want economy drive, thus using box shift method would get to optimum speed quicker than conventional shifting.

Quite alot of variables to consider... :S

VAG actually did a study on this for diesels some years back (sorry no weblink), and the answer may surprise you. Provided you maintain constant upshift revs, it is equally fuel efficient to accelerate hard as to accelerate gently.

Nice,

At 33-35mph I'd probably hang on 4th on the fabia (at ~1.5k), rarely would go to 5th due to low rpm ~1k.

Anyway the way I've been taught was to box shift upwards (2nd -> 4th etc) to be more economical, of course this will imply using more of the rev range at lower gears. So, one wouldn't really want to hang on high rpm for a long time if they want economy drive, thus using box shift method would get to optimum speed quicker than conventional shifting.

Quite alot of variables to consider... :S

The Octy's a heavier car, but I'd agree; you want to be in 4th for speeds in the 30s; maybe 3rd if you might have an oportunity to accererate.

Block shifting is really only advantageous if you've, say, overtaken a tractor and are now doing somewhere in the high 40s in second or 50s in th 3rd.