Safe Speed Forums

Hi All,

It is sensible and permissible to overtake when there is oncoming traffic so long as the oncoming traffic is distant enough for safety.

When one does a lot of overtaking it is useful to maintain a safety calibration check: "was that too close to the oncoming vehicle or not?"

I have long counted the time in seconds between fully returning to my lane and passing the oncoming vehicle. Two seconds seems a viable minimum.

Two seconds is not by any means the entire error margin because it is also possible to cut in earlier after overtaking. Generally I wouldn't start to pull in until I've got a full one second gap from the target vehicle, and it normally takes several seconds to gain that additional distance. In an emergency one could pull in much sooner.

What do others think?

Does anyone else use a "brain calibration check" for overtaking safety?

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Overtaking is an activity that requires one to have judgement of the distance to an oncoming vehicle, judgement of that vehicles speed, and knowledge of you own vehicle's performance. In addition it requires a sense of the likely range of responses of the vehicle you are about to pass - is it likely to speed up?

This problem becomes greater as average speeds increase, and as your vehicle acceleration decreases (for example tha cceleration of heavy trucks).

In many higher speed situations a 2 second margin would be too low.

For very heavy vehicles the distance travelled during passing may be 1500 metres or more - which means the distance to the oncoming vehicle could be 3000 metres or more. How oyu can accurately judge a vehicle's speed at 3000 metres is an interesting concept - the included angle is 0.06 degrees and the rate of change per second about 0.001 degrees.

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John Lambert

John,

You make some excellent points. I've certainly been extremely worried from time to time about the distance required when heavy vehicles overtake one another. In the UK this is worsened by the compulsory fitting of 56mph speed limiters to heavy vehicles. Such limiters often result in 3 miles overtakes on dual carriageway roads and motorways. The effect on single carriageway roads hardly bears thinking about.

However, I was thinking about a rather different situation (and I accept that I should have made it clear). I was thinking more about medium to high performance vehicles and regular - even constant - overtaking.

I was once (more than 15 years ago) a passenger in a vehicle driven skillfully at speed by a highly qualified police driver. He was overtaking constantly and generally very competently. However, in the course of an hour or so he probably caused about 20 oncoming vehicles to flash their headlights. I believe he was cutting the margin too fine. It made me think about how large the margin should be, and how it might be specified.

I have never seen written down anywhere a recommended method for checking the margin, and I recognise that unless we have some sort of standard the brain can allow "calibration drift" possibly towards the point of actual danger. It makes sense to define some sort of minimum standard.

Whatever that minimum standard should be, I'd like to have a go at defining it. My "two second" rule of thumb is reasonable for the range of roads and vehicles I normally drive. If anyone has any better ideas, I'd love to hear about them.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

During 4 hours training with a Police class 1 driving instructor one of the points he raised was that I was allowing too much margin before pulling in. During the whole time I never got flashed by an oncoming car either and the point of the exercise was to "make progress". I can personally recommend "Ride and Drive" for further training.

I couldn't agree with you more about the benefits of additional training. I took most of my advanced and high performance training in the 1980s and have not met the people from "Ride and Drive".

It is possible to cut in quite tight after overtaking without causing too much in the way of danger. (Note that I am absolutely not advocating pulling in tightly enough to alarm the target vehicle's driver, let alone causing him to alter course or speed).

But how tightly one pulls in contributes to the overall safety margin. I guess we'd need two definitions then - one for the tightness of the pull in, and another for the time until any oncoming vehicle passes.

Without putting actual numbers to either of these margins, how could any of us be certain that we won't gradually allow the judged margin to change over say, 10 or 15 years of regular driving? And that's really my whole point. I want to quantify the margin with a rule of thumb.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Paul, I don't think you can put a figure on it. If you want to "make progres" safely I don't think there is any substitute for extra training.

I am often asked why I overtake with oncoming traffic clearly visible. It simple - I like to see whats coming, far safer. No nasty shocks everything in view. Sadly most drivers don't realise that on most roads there is room for four vehicles abreast so three is really no problem.

Occasionaly people flash at me, but I give them a cheery wave, these are the sort of people that aspire to drive Volvos. I used to have great fun delivering wet fish but now the roads are so crowded and it seems that most drivers take advice on mobile phone while aiming their vehicles. Standards are dropping - how many people wash their cars weekly? When did you last see a Wemouth triangle in the rear window? or see a policeman directing the traffic?

Regards
Les Chalards
Master of Fishmongery (retr.)
V.O.C.

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If there are any fellow gene splicers out there, please check out my website and we can swop stories. http://www.leschalards.o-f.com/

I agree about further training. Since I moved to North Scotland in 1990, I have not found any potential trainer who knew anywhere near as much about it all as I do.

If I'd had both time and money simultaneously, I'd have travelled "down south" to get some further training. I do certainly feel I'd benefit from a day in the car with the right chap.

But we still need some numbers, or another method of checking calibration. Training is one thing, self checks of performance and judgement are entirely another.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

You should do lots of overtakes, maybe 30 or so. Get someone to come with you (or use a tape recorder). As you start the overtake call out how many seconds gap you think there is going to be between you getting back in lane and the car passing you coming the other way. Measure the actual time as well.

Then, work out the difference between the predicted and actual time for every overtake, then work out the standard deviation of this error. You should probably then aim for 3 or 4 times standard deviation to make sure you never need to swerve in dangerously.

Just an idea, probably wouldn't really work in practise (or theory!), you'd probably get a gap of 20 seconds or something!

Les, that's an interesting view point - I have often found that on a long straight road it "feels" better when you *know* something is there, rather than waiting for that surprise. WOnder what the reasoning for this is? something holds me back sometimes on empty road, yet the sight of a distant approaching vehicle somehow lends perspective. Weird. I thought me & the missus were the only ones. Maybe there are more quirks like this in the risk vs reward equation? Perhaps we all need a little stimulation in our driving to keep it interesting, and by extension, keep alert and therefore safer..

Keep it shiney side up folks.
C

(hi Paul!)

IMHO, it's because once you see the approaching vehicle, you have a point of reference that is easier to judge. I find the wait to see the opposing vehicle phenomenon happens less on roads that I know well. Something in the back of the mind (Call it experience!!) tells me to hold back until I know I can judge the gap accurately.

I am always happier with leaving myself a 50% margin, must come from the days of driving old bangers that occasionally spluttered at innoportune moments

I still like to use enough power to carry me through the manouvere so that if the engine cuts out I can still coast to safety and complete the overtake.

Surely speed differential between overtaker and overtakee is a variable which should affect this? If you can drop down a gear or two (I would usually want to be in the lower gear already, anticipating the overtake), and accelerate hard once a suitable gap presents itself so that by the time you are abreast of the overtakee there is (say) a 20mph differential, you could surely cut back in a lot sooner than at a speed differential of (say) 10mph without causing alarm. Clearly this also requires sufficient space ahead of the overtakee so that any excess speed can be lost without braking.

I think that's why the rule of thumb calibration check I've been playing around with doesn't start its count until you have returned to your own lane. It then covers both the differential speed to the overtakee and any need for braking.

btw, I do almost all the braking (when braking is required) on the offside in a straight line and only then move left into a gap. This has a whole series of advantages:

If the opportunity to overtake another vehicle presents itself you are ready to go.

It avoids "rushing up the rear" of the vehicle in front - I find that a very uncomfortable part of many drivers' overtaking technique.

It allows the vehicles on the left time to acclimatise to your intention to return to the left.

Braking in a straight line is always preferable.

you can usually see more from the off side position.

There might well be a couple more good reasons too.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

... so avoiding braking after you've returned to the nearside lane. I think this is an acid test. If you have to brake after you've returned to the nearside lane then, de facto, there was insufficient gap for the overtake (or the overtake speed was misjudged).

Not sure that your rule of thumb idea is practicable. How can you accurately anticipate the time to coming abreast of the approaching vehicle after allowing for any braking you MAY have to do in order to return to the nearside lane allowing sufficent distance from the following vehicle (which clearly depends upon the speed differential you've estabished during the overtake which in turn may depend (inter alia) on the perceived gap available).

It's a helluva lot harder to measure than the two second gap principle for traffic ahead.

Agreed, except you can't make any judgement after overtaking an isolated vehicle on this basis. I overtake a lot of isolated vehicles.



The rule of thumb may be far from perfect, but I'm sure it's better than nothing, and I expect there's room for improvement.

Let me turn the question around, and ask folk:

If you see an overtake and judge it to be "only just safe" (in terms of the gap to oncoming traffic), what criteria do you employ to make that judgement?

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Unfortunately, this is inevitable sometimes.

Living in a rural location, I very often find myself faced with the prospect of "convoys". One slow driver at the front and a line of 6 or 7 behind them, too cautious to attempt overtaking. A part of my livelyhood depends on being summoned to places as soon as possible and as a consequence, I find myself having to pass cars more regularly than others.

The main problem you will have is that in the "convoy", there will be little braking distance between vehicles. I find these convoys totally unacceptable and infuriating.

If there is a driver on a NSL single carriageway road who is travelling at 40mph, all it takes is one or two drivers behind them who are too nervous to overtake and then before you know it the two cars have become 5 then 6 then 7 ad infinitum.

I feel the driver of the car at the front (who, in my experience, are almost always senior citizens) have a moral obligation to pull over and let the following traffic pass. Indeed, there is a strong case for a legal enforcement of this situation as it causes frustration and, invariably, accidents.

The old saying of "well I am travelling below the speed limit so I ain't doing anything wrong" needs to be stamped out.

To return to the point! When faced with the closely bunched "convoy" scenario. You end up overtaking 2 or 3 cars at a time when safe to do so. As a consequence you have picked up a fair bit of speed and when you do indicate to pull in, sometimes it is unavoidable to apply the brakes, causing the driver behind to make less than civil gestures to you!

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cheers,
DM

Demolay:

I'm not sure that you read my last post correctly. I am advocating doing *all* your braking on the right hand side of the road. When you pull left, no speed differential remains.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Hi Paul,

I did read your last post. My statement still stands.

Often it is necessary to get into the left lane faster than you would like. Just the other day I passed 4 vehicles on one long straight road. The speed limit was 60mph and a tractor was holding the traffic up. I judged the distance ahead clear enough to attemp an overtake of all 4 vehicles who were travelling at no more than 40mph.

As I was passing the second vehicle (doing about 55mph at this stage) a motorbike travelling in the opposite direction came into my line of site obviously travelling at a ridiculous speed. I had little alternative but to pull in as quickly and safely as possible. I can only speculate as to the biker's speed, but it was certainly 90mph+. In my rear view mirror the gentleman that I pulled in front of actually smiled and waved as if to acknowledge the situation.

You cannot legislate for that kind of thing happening. That is why sometimes you are left with no choice.

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cheers,
DM

Lucky you. The south-east's a bit more crowded.



The real problem is that it's not a guide to whether you can overtake safely but whether you HAVE overtaken safely - i.e. a retrospective test. I'm not sure that it is possible to try and measure the 'prospective' safety of an overtaking manoeuvre in this way. Similarly, you argue (and I agree) that you don't measure safe speed in miles per hour.



I don't try to measure it by applying objective criteria. It's a speed/distance judgement similar to turning out of a junction (probably more complicated). Depends on car peformance, road condition, other traffic (and, realistically, if perhaps improperly, state of mind). However, I'm happy to learn something new.

Can I ask why you have particular interest in this? Are head-on collisions during an overtake a significant contributor to road accident casualties/fatalities?

I agree it can be difficult to avoid if you want to be able to make progress.

However, the reason for that, and imo the single most common and serious driving fault exhibited on the roads is "FAILING TO LEAVE AN ADEQUATE GAP TO THE VEHICLE IN FRONT".

I believe this single fault, if eradicated or significantly reduced, would do more to improve road safety than anything else. It accounts, directly, for collisions and indirectly for traffic bunching, congestion, stationary traffic approaching an obstruction, frustration leading to unsafe overtaking and perhaps more. This is not scientific observation, more instinct. In the circumstances you describe, an adequate gap would make the overtaking much easier and reduce or eliminate the need to brake.