Safe Speed Forums

I'm starting a new thread (at Paul's suggestion) in the hope of a less emotional debate to examine the question of who should have priority in an overtaking conflict scenario.

Let's say there is a truck in L2 of a motorway at 50mph; a car some distance (say 6s separation) behind it in L2 at 70mph ("P1") and another car some distance (say 6s separation) behind P1 in L3 at 90mph ("P2"). In order to avoid conflict at the pinch point, either P1 must reduce speed and allow P2 to overtake itself and the truck first, or P2 must reduce speed to allow P1 to overtake the truck first.

Who has/should have priority?

My opinion is P1 has priority if, but only if, it takes its position in L3 in sufficient time so as not to force P2 to brake with moderate or greater force. If all that is required is for P2 to lift off or brake gently, P1 is entitled to go first. That priority, imo: (i) is more clear cut if P2 is carrying greater speed than is commonly the case for the road in question; and (ii) is absolute if P1 is driving at the speed limit; in both cases (but more so in case (ii)) because it is incumbent on P2 to anticipate P1's likely move in good time to avoid a conflict, in fact to take sufficient, early action to preclude any possibility of conflict.

Good. Thanks for posting this. It IS interesting.

We can establish some 'end points'.

Clearly if the L3 vehicle is a mile back the L2 vehicle should 'go first'.

And clearly if the L3 vehicle is already alongside then the L3 vehcile should go first.

So we know that the potential conflict only exists in some 'middle ground'. It follows that there's a 'changeover point' in some arrangement of vehicles where practical priorities switch.

Looking at it from an 'advanced' point of view, the best action is to make the conflict disappear. If I'm in L3 I may well give way. Sometimes a headlamp flash is sufficient, but can be ambiguous. Switching to L2.5 gives a VERY clear signal, and I do this from time to time.

If I'm the L2 vehicle (and I have the performance) I'll match the L3 speed (assuming that it's safe) and go first. If I don't have the performance, I'll likely give way and show a flash of brake lights as signal if it is safe to do so (i.e. quiet conditions). If it's not safe to flash the brake lights, I'll probably give a single flash of the left indicator.

But none of this really answers Observer's question. I just choose to 'stretch' the changeover zone and avoid the question.

I don't really agree with forcing another vehicle to change course or speed by my actions (as distinct from 'by my presence').

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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

Probably just me being a dumbass, apologies if so, but could you clarify what you mean by 6s separation?
Do you mean ‘P2 would take 6 seconds to arrive where P1 was at t=0 (240 meters apart)’ or ‘P2 will have caught P1 in 6 seconds at the given differential speed (54 meters apart)’?

Isn't this the key to considerate driving, and if everybody thought this way we would have a lot less conflict. But of course COAST is required to ensure that you are fully aware of the other vehicle in the first place.

I personally will judge whether the conflict is going to occur, and then take one of two actions depending on the conditions. Assume that I am P2:

1) If it is obvious that P1 will have to take action to assist me, i.e. to let me past they will have to brake, then I will clarify the situation to remove any doubt, by accelerating so that I am past them before they need to take any such action - a positive move (although illegal because I will be speeding) removes doubt and everybody moves though with no hassle.

2) If P1 has already closed to the point of having to brake, and I am comfortably behind them, then I will lift off, and if they have the decency to indicate "please let me out", then I respond with a quick double flush "go on then". If they think that I am too close already and make no move to pull out, then I will pass them, but should they chose to just pull out, then I have already slowed and am ready for such a move - although I will often let the gap close to indicate my disapproval of being cut up (not too close though).

The key is to remove the ambiguity, and the worst thing that you can do is to just sit on their shoulder, as they then haven't got a clue what to do. This is where the draconian enforcement of speed limits becomes a real problem because it is effectively removing option 1 completely, and forcing the worst case situation.

Sorry for lack of clarity. I meant a position where P1 and P2 would have (arbitrary number) ~6s to decide what they are going to do. Enough time for a considered judgement but close enough to make action necessary.

I would also do that but only if I can get past before it's likely that P1 will be considering his move or if I can clearly see (e.g. on account of change of speed) P1 has already 'given way' to me. There is a danger that P2 increases speed to squirt past ahead of P1 at the same moment as P1 increases speed to squirt past ahead of P2.

Indeed there is, but the gap between P1 and P2 will not close, while the gap between P1 and obstruction does, so it switches to scenario 2. Always be ready to switch to the passive option.

In general these decisions are made well in advance, and I should be well clear of P1 before they have to make a decision. In many cases it is obvious that they haven't even started to think about it!

I personally don't have a problem with letting people out - even trucks, any brief slowing down will make little difference and I can make it up easily, but it does get aggravating when they pull out in front of you (normally without indicating), and then don't move back in again when there are obvious gaps - such as nothing in L1 or L2 for at least 30 seconds (as in it will take 30 seconds to close the gap). But rather than flashing lights, hooting horns and examining the small print of the stickers on their rear windscreen I would pull into L1 and undertake with a completely empty lane between us. But I do have generous acceleration available

An interesting question.

My approach is determined by my observation and assessment of the developing situation.

If I am the driver of P1 I will have estimated the speed of the vehicle and if it is possible for me to accelerate smoothly and responsibly to complete my manouver before causing P2 to brake I will make that decision and execute. If I would have to accelerate either harder or to a greater speed than I feel would be safe then I give ground and wait till P2 has passed.

In the case of P2 I am always prepared to give ground as accelerating into a developing hazard is undesirable.

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Former Military Police Officer and accident investigator

Overall I must agree with Patch here in both cases. In the case of P1 the importance of having left a good space between your vehicle and the one in front (the one to be overtaken) cannot be understressed. This allows for some acceleration whilst observing the approach L3 vehicle and allows this to be scrubbed off without hazards if the L3 vehicle speeds up in response.

It will, though, if P1 accelerates from 70 to 80 and P2 simultaneously accelerates from 90 to 100. Added to which, the time to the pinchpoint is reduced because both cars are now closing on the truck at higher speed differential. I think Patch's point about not accelerating into a developing hazard is the text book answer.

On the general point, the applicable guiding principle, imo, is that the overtaker must keep clear of the traffic being or intended to be overtaken. This must include making allowance for the reasonably predictable behaviour of the target vehicles.

IMHO, the trucks shouldn't be doing this speed in the middle lane (especially when the overtakee is doing 49.5mph, lol)

Your case study is an example of how this causes confusion, danger, and ultimately, congestion.

And there's really only one answer...but that's a story for another day.

Welcome to the site BTW.

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Science won over religion when they started installing lightning rods on churches.

I would take into account how long the HGV overtake was likely to hold me up, and whether P2 in L3 was the only vehicle coming up behind, or the first of a long line.
If it were the latter, I would already be indicating (showing a desire to pull out), and looking for a sign that L3 was going to acceed, or whether it was safe to pull out and accellerate to reduce the inconvenience to the L3 driver.

The point at which this becomes more critical, is if instead of an HGV in lane 2, you have a driver or line of drivers, who fail to return to l1 having completed their overtake, and elect to take a "Grand Tour" of the middle lane of the M6.
You are then faced with either a protracted overtake in Lane 3, an pointless cruise in lane 1 or joining the queue in L2.
The only other option being an undertake in L1 with associated dangers.

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Time to take responsibility for our actions.. and don't be afraid of speaking out!

From what I see, most people opt for L2 queue option - which just increases the L3 problem exponentially

I can never easily take the L3 option, as I end up thrashing my poor car and getting bore down on by the type of driver sixy-the-red encountered

I hate passing them on the left though (is it illegal or not???) because not only is it dangerous, I know they'll be blocking me in again within minutes

Interesting slant on this. It depends on your interpretation of keeping up with traffic in your lane...

_________________
Time to take responsibility for our actions.. and don't be afraid of speaking out!

Swap "left" and "right" and remove the two "not"s in there and you have the American version of that rule!
"Do not" is not a "MUST NOT" so I say that overtaking on the left is "not ilegal".

I find that if I am P1 (ie. I want to overtake but that would mean me getting in someone's way) I will wait and let them past.

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Andrew.

I would say that P2 had priority unless P1 could make the manouver without P2 having to slow at all. For the simple reason that P1 is having to change lanes. If you are making a rule then better to keep it simple and unambiguous.

But. It would be common courtesy for P1 to back off and allow P2 to pass through.

Perhaps I would say priority belongs to the driver who would otherwise have to brake the most.

In other words, if P1 had to brake all the way to 50 to let P2 go past, he should have priority (assuming P1 wasn't tsm and he accelerated to ~80 while overtaking, P2 would only lose 10mph)

On the otherhand if P1 only had to ease off by 10mph to let P2 past, then he/she should do so.

I see the point you're making, and it's fine in theory, but who thinks in terms of numbers when they're out and about on the road?

Being a lorry driver, I find myself in the position of having to come out of L1 to overtake slower traffic a lot. I never do what so many of my "professional" colleagues do and just pull out with one flash of the indicator: I sit in the inside lane, well back from what I need to overtake, until there's a safe gap for me to pull into. Or, if there's lots of traffic in L2, I wait until there's space in L3 for anyone in L2 to pull in to, then indicate. Then when someone has moved over to let me out, off I go. Overtaking traffic, as far as I understand it, has right of way.

Yes they do. But at {some earlier time} they are not yet 'overtaking traffic'. It's the transition zone that causes the issues that we're discussing here I think.

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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