Safe Speed Forums

I suppose I had a near miss today. It was pretty low level...

I'm in a London one way system, just south of the Thames. It's five lanes wide. About 150 yards ahead the right lanes go right and the left lanes go straight on. I'm in L4 because I'm going right and I'm not sure if three lanes go right or two lanes go right. There's no other traffic nearby except a modern Volvo saloon in L5 behind me and gaining on me.

At about the same time that I'm discovering that three lanes go right the Vovlo is passing me. Despite the fact that there's nothing ahead of the Volvo I realise that he's coming into my lane in a really very odd manoeuvre. He's not indicating, but by the time his windscreen is level with the front of my campervan, he's already about a foot into my lane and coming fast. Looks like his rear nearside door will hit my front bumper.

I wound on about 120 degrees of left lock with both hands still on the wheel in the original position. (Why did I do it that way?) The Volvo kept coming, but I'm steering away from him enough. There was an element of 'waiting for the crunch' and I'm sure that the gap went as low as six inches.

I just about encroached on L3, I suppose, but anyway I knew L3 was clear. It was all over in a flash with no impact.

As it turned out 3 lanes went right and I followed the Volvo round the right turn with both of us needlessly in what was now L2.

I didn't brake and I don't really know why not. Did I assess that there wasn't time? If there had been a crunch, It would only have been a bumper scratch for me and a dented panel for him.

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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

I find it very interesting to analyse our reactions when we get into a situation like this, as what we do in a split-second decision tells us loads about what we've learned [or not!].

We don't make conscious evaluations when things happen that quickly, we simply react according to learned or instinctive responses, then we rationalise them after the fact. So here goes with my rationalisation of your two "reactive" inputs...

I'd say that deep in your experience you had an awareness that a sudden severe swerve might lead to equally sudden oversteer. Regardless of what your conscious "IAM" mind might theorise, I'd say that your subconscious mind is dialled in to the fact that fixed input steering is far and away the most accurate method of applying opposite lock, because (i) your hands are returning towards where they started, and (ii) they know where "straight ahead" is, which is usually the most critical thing in getting the back end back into line.


Two snap decisions here I reckon:
1. You had two possible reactions available: steer and/or brake. Problem is that either one compromises your ability to do the other [friction circle]. In this instance your mind made a quick "time on distance / trajectory / momentum" prediction and decided that steering was going to solve things and therefore threw all the eggs into that basket. To put it another way braking wasn't going to open the gap up as quick as steering.

2. Going back to the earlier point, if your subconscious mind was anticipating possible oversteer [perhaps evidenced by the snap decision to fixed-input steer] then keeping off the brakes would be part of the same decision making process, to avoid forward weight transfer unsticking the rear tyres.

As a matter of interest, does the "bus" have a tendency to oversteer in situations such as this, or (perhaps more importantly) are you aware of or would you expect any such tendency?

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Hell, yes. I agree with your analysis. There were probably very good reasons for the method selected by something deep in my subconscious.



With most vehicles I would willfully explore the edges of the handling envelope soon after I started driving. But doing that in a campervan makes things inside fall over and fly about, so you really can't and anyway I haven't.

I did get some serious understeer once on gravel at (what?) 15mph, while turning 90 degrees left into a set back layby. That's the only limit-of-grip experience that I've had in over 20,000 miles now.

The suspension is dead crude - the front is suspended on a transverse leaf spring and isn't even independent. The rear is live axle and leaf springs.

Yesterday in the one way system, the input wasn't violent and didn't approach limit-of-grip. But I think you're right in as much as if it had been limit-of-grip, I was well placed to catch it.

But if you think about it, adopting a technique that's appropriate to limit of grip is also likely to maximise the margin from limit-of-grip even in circumstances where limit-of-grip isn't approached. This is where track driving meets road driving. In both cases we're trying to maximise grip, but on the road we're looking for margin, while on the track we're looking for speed.

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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

Now there's an interesting paradox!

To take this one step further: on the track we're looking to get as close to the limit of grip as possible, on the road to get as far away from it as possible; yet the same techniques serve both purposes.

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Nah. On the track we're trying to use 'never more than' 99.999% of grip, on the road we're trying to use 'never more than' xx%. In my case I'm happy on the road where xx is never more than 50%.

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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

[quote="SafeSpeed]

With most vehicles I would willfully explore the edges of the handling envelope soon after I started driving. But doing that in a campervan makes things inside fall over and fly about, so you really can't and anyway I haven't.
.[/quote]


Paul - from what i have seen this is a VW camper - and on tight roads most VW vans ( AND pickups are very good --my cousin could demonstrate that ) - anyway point is from my work around north in vans - idea is to driveproof the van - to make most things impervious to the road - i used to have to take a loaded van to places like Ardumurchan light - etc etc .I soon found that the only way to travel thies sorts of roads was to driverproof the van and kit.

Mild suggestion - stops things flying around the back.

That sounds very strange and I wonder what on earth was going on in the other driver's head.

With all the benefits of hindsight, given another car moving across ahead of you, hard braking would have been sensible. It's amazing how hard you can brake before you compromise lateral grip significantly, circles are funny old things and you really can get 0.7G backwards and 0.7G sideways at the same time.

Also, if in doubt GET ON THE HORN. It doubles the number of people reacting, and may wake them up to their mistake before they have pushed you into a violent avoiding manoeuver. Luckily in this case it seems you did have the space you needed to avoid them, but another time you might not be so lucky. If your instinctive reaction avoids one collision but causes another YOU would be at fault. I believe that sounding the horn also puts you in a better position in terms of negotiating blame/liability since it shows that you were aware of the situation and taking reasonable steps to avoid the collision. No horn and no 3rd party evidence that they drove into you could leave them claiming that you drove into them while you were in their blindspot, strongly implying that it was all your fault.

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Peter Humphries (and a green V8S)

I think, with the benefit of mega-hindsight, that I didn't brake because the speed differential was already big enough.

I very much agree with the general point about honking, but I know that I knew I wanted two hands on the wheel. With a centre-mounted horn push, it isn't always available in 'swerving' situations.

That's an interesting Pythagorean point about (friction) circles. I don't believe that I'd noticed that apparent advantage before.

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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

Don't forget that when braking there is also a weight transfer forward increasing grip to the steering tyres, but once they slide you move from a static friction to a moving friction scenario and the grip level is substantially reduced (for both braking and steering). This is why ABS works at retaining steering during heavy braking - it doesn't reduce braking distances as such, but it does retain the ability to steer.

Good point about weight transfer. That's how trail braking works.

I think the tyre/tarmac interface is too complex for 'static' and 'dynaminc' friction rules to apply. We know, for example, that 'a bit of slip' increases friction. See figure 8 on http://www.safespeed.org.uk/braking.html

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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

It is alas, illusory though, as of course 0.7g forwards + 0.7g laterally resolves to 1g at a 45 degree vector.

Where I think you really gain by overlapping steering and braking in "dodgy" situations is that as soon as you brake - even if you are still at a 90% steering / 10% then you start reducing speed; and once you start reducing speed then steering the same cornering radius requires less of the available grip, so now a split of 80/20 gives you the same cornering ability. Of course now you have 20% grip available for braking so you can shed speed more quickly, yielding more "free" grip in a sort of beneficial vicious circle!

The big problem is managing the weight transfer, but if you can do that then just a tiny initial braking input while you steer can pay back a big divdend very quickly.

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I don't know about illusory. More than half braking + more than half cornering sounds pretty cool, and of course it's real.



Two more things about braking and cornering...

- The forwards weight transfer can give more turn in bite

- You can use the brake as an attitude control (varies the balance of grip front to rear).

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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

Yes, but they can't be considered in isolation in that way. In reality they simply resolve to a 45 degree vector where 0.7 + 0.7 = 1.0g!

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CSCP Latin for beginners...
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Yeah yeah - I know. I did say 'Pythagorean'.

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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

Thought he dealt in triangles (those things with tree sides )

Didn't he also leap naked from his bath, ran down the street in the buff yelling "Eureka, Eureka!"? Or was that his erstwhile countryman Archimedes? Ah well, so he got to the nuthouse first
Having too much knowledge swilling around in too small a space does that to you!

I think when you analyse it, you should ask if you could do it better - and as suggested, fasten everything down, and go try it!

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