Two second rule

[AF62]

Heading around the M25 on Friday I really saw the benefit of the ‘two second’ rule.

Traffic was busy with the variable speed limit signs in operation limiting speeds to 60 or occasionally 50, but the traffic was moving along at those speeds.

And then it wasn’t.

Four lanes of traffic suddenly slowing as a ‘ripple’ made its way backwards quickly. As I pressed the brake heavily I was not too concerned as I had left a reasonable gap with the cars in front.

And then I looked in the rear view mirror.

‘Oh dear’ I thought, or words to that effect, as I could see the two cars and then a truck that hadn’t done the same.

The one immediately behind was slewing from side to side as it tried not to plow into the back of me, so it seemed judicious to ease off the brake a little to ensure that wasn’t the case even if it did mean ending up closer to the cars slowing in front.

And then there was, almost cartoon like, dust thrown up and the sounds of crashing as the cars and truck behind were not so successful.

Then as quickly as it had appeared the ripple vanished and the traffic moved on again and half a mile later the variable speed restrictions stopped.

[Dod101]

I assume you did not stop to see the damage? As you have shown there is only so much that you as the driver can do to protect yourself and that is the danger in that sort of situation. But good for you and sounds like a lucky escape.

Dod

[Mike4]

Heading around the M25 on Friday I really saw the benefit of the ‘two second’ rule.

Traffic was busy with the variable speed limit signs in operation limiting speeds to 60 or occasionally 50, but the traffic was moving along at those speeds.

And then it wasn’t.

Four lanes of traffic suddenly slowing as a ‘ripple’ made its way backwards quickly. As I pressed the brake heavily I was not too concerned as I had left a reasonable gap with the cars in front.

And then I looked in the rear view mirror.

‘Oh dear’ I thought, or words to that effect, as I could see the two cars and then a truck that hadn’t done the same.

The one immediately behind was slewing from side to side as it tried not to plow into the back of me, so it seemed judicious to ease off the brake a little to ensure that wasn’t the case even if it did mean ending up closer to the cars slowing in front.

And then there was, almost cartoon like, dust thrown up and the sounds of crashing as the cars and truck behind were not so successful.

Then as quickly as it had appeared the ripple vanished and the traffic moved on again and half a mile later the variable speed restrictions stopped.

There is a further dimension to this, I notice as a high mileage motorway driver. Like you, I always leave a bigger gap in front of me on motorways than other drivers seem to think is appropriate, mainly having spent an informative hour or two watching youtube videos of motorway accidents taken from the monitoring cameras, which illustrate the effect you describe.

But there is more. I have discovered when you maintain a plenty-big-enough stopping distance yet the cars in the lane next to you haven't, when the ripple comes and you are glad of your generous braking distance, a car in the lane next to you will often swerve into your braking space (thanks to ABS) to avoid them hitting their car in front. At this point all your prudent safety margin gets eaten up.

I've had this happen to me, it is highly disconcerting and yet another factor to bear in mind when motorway driving. In poor conditions I think it a good idea to drive in the nearside lane so one can oneself swerve onto the hard shoulder, should another car swerve in front of you nicking your safe stopping distance.

(Edit to swap around two words typed in the wrong order.)

[swill453]

I make it a personal challenge when driving to use the brake as little as possible. This has multiple benefits:

- keeps you alert as you're looking multiple cars ahead for potential slowing incidents
- make you drive more smoothly, saving fuel
- saves wear on brake pads and disks
- you tend to leave a safer distance between you and the car in front
- often you actually get to stop the propagation of the ripple effect, as if you manage to avoid braking then the vehicles behind may not have to, and it dissipates

Note I have an automatic car, therefore less engine braking, so makes the challenge a little harder, but not impossible.

Scott.

[tjh290633]

It helps to keep an eye on the brake lights of the cars ahead of the one immediately in front of you. Not always easy if you are behind a bulky vehicle, but you can easily position yourself to see past it if possible, due to road curvature..

TJH

[Mike4]

I make it a personal challenge when driving to use the brake as little as possible. This has multiple benefits:

- keeps you alert as you're looking multiple cars ahead for potential slowing incidents
- make you drive more smoothly, saving fuel
- saves wear on brake pads and disks
- you tend to leave a safer distance between you and the car in front
- often you actually get to stop the propagation of the ripple effect, as if you manage to avoid braking then the vehicles behind may not have to, and it dissipates

Note I have an automatic car, therefore less engine braking, so makes the challenge a little harder, but not impossible.

Scott.

I drive an automatic and I can get as much engine braking as I like. On mine I can force it to drop a gear (or two, or three) by momentarily pushing the selector to the left. One gear ratio dropped per push. And conversely I can change up manually by pushing the selector lever to the right.

This is the only auto I've ever had and people look doubtful if I tell them about this. Is it not normal on autos?

[richlist]

My Mercedes operates in exactly the same way using the gear shift.
Automatics with paddle shifts on the steering wheel can achieve the same effect.
In addition my cruise control can lower or raise the speed by 5mph for each pull of the lever.

[swill453]

I drive an automatic and I can get as much engine braking as I like. On mine I can force it to drop a gear (or two, or three) by momentarily pushing the selector to the left. One gear ratio dropped per push. And conversely I can change up manually by pushing the selector lever to the right.

This is the only auto I've ever had and people look doubtful if I tell them about this. Is it not normal on autos?

Mine is actually a DSG (direct shift gearbox) with flappy paddles on the steering wheel, so I can do similar. Though it's probably not a great idea to whack it down too many gears at once or you slow down sharply without brake lights to warn the vehicle behind.

Scott.

[AF62]

But there is more. I have discovered when you maintain a plenty-big-enough stopping distance yet the cars in the lane next to you haven't, when the ripple comes and you are glad of your generous braking distance, a car in the lane next to you will often swerve into your braking space (thanks to ABS) to avoid them hitting their car in front. At this point all your prudent safety margin gets eaten up.

That was what was happening to the car behind who was trying to stop before hitting me, but as I was in 'lane 4' (or 5 or 6, I lose count around the M25 of how many lanes the widest sections are!) they were trying to stop their car steering into the concrete barrier in the centre of the motorway.

I've had this happen to me, it is highly disconcerting and yet another factor to bear in mind when motorway driving. In poor conditions I think it a good idea to drive in the nearside lane so one can oneself swerve onto the hard shoulder, should another car swerve in front of you nicking your safe stopping distance.

Trouble is then you have the 'knights of the road' in their HGVs with 2mm of space behind you if you are not going fast enough for them, and if you are then repeatedly overtaking into the middle lane into the inevitable queue of traffic there where someone willing to let you pull out is rare.

[JohnB]

I'd hope that clever cars would put on the brake lights if the car was slowing because of engine braking, regen braking in electrics or actual brake pedal use. Just having the last removes the alert signal from the following driver, who can then assess the distance between the cars narrowing.

If you have time when breaking heavily, check mirrors and put on hazard warning lights. Certainly worth losing your safety margin to avoid being rear-ended, and having front and rear dash-cams to show who's at fault if there is a collision.

[swill453]

I'd hope that clever cars would put on the brake lights if the car was slowing because of engine braking

That's not something I've ever heard of a car doing, though it's not impossible of course.

If you have time when breaking heavily, check mirrors and put on hazard warning lights.

Now that is something that some modern cars do automatically.

Scott.

[AF62]

and put on hazard warning lights.

That is one thing that some car manufacturers, such as Ford, help with - a large clear button in the middle of the dashboard you can easily hit without taking your attention away from dealing with the issue.

Unfortunately the car I was in the hazard warning light switch is an unremarkable thing buried amongst a group of other unremarkable switches low down on the console so you need to take your eyes off the road to find it and accurately press it.

Fortunately my wife recognised what was happening and pressed it whilst I was otherwise occupied.

[servodude]

isn't a part of this that while a lot of people "know" about the two second rule counting starts from one and the name of the rule doesn't make it clear that you should continue to the number three to get the required period?

What could help?
perhaps involving the Pythons to construct a better rule
or
rolling out classes in the C programming language so that people start to, correctly, count from 0

- sd

[Breelander]

isn't a part of this that while a lot of people "know" about the two second rule counting starts from one and the name of the rule doesn't make it clear that you should continue to the number three to get the required period?

What could help?

To time 2 seconds reasonably accurately, recite to yourself "only a fool breaks the two second rule"

[servodude]

isn't a part of this that while a lot of people "know" about the two second rule counting starts from one and the name of the rule doesn't make it clear that you should continue to the number three to get the required period?

What could help?

To time 2 seconds reasonably accurately, recite to yourself "only a fool breaks the two second rule"

Yup that seems to work nicely

[redsturgeon]

isn't a part of this that while a lot of people "know" about the two second rule counting starts from one and the name of the rule doesn't make it clear that you should continue to the number three to get the required period?

What could help?

To time 2 seconds reasonably accurately, recite to yourself "only a fool breaks the two second rule"

Yup that seems to work nicely

Yup, ten syllables as in "One Mississippi two Mississippi."

I think it was suggested in the original advert.

John

[chas49]

I'd hope that clever cars would put on the brake lights if the car was slowing because of engine braking

That's not something I've ever heard of a car doing, though it's not impossible of course.

Discussed in this thread https://lemonfool.co.uk/viewtopic.php?f=58&t=31402

[swill453]

I'd hope that clever cars would put on the brake lights if the car was slowing because of engine braking

That's not something I've ever heard of a car doing, though it's not impossible of course.

Discussed in this thread https://lemonfool.co.uk/viewtopic.php?f=58&t=31402

That turned out to be about regenerative charging, and not IC engine braking, which is the specific part I was highlighting.

Scott.

[pje16]

I'd hope that clever cars would put on the brake lights if the car was slowing because of engine braking,

Similar I guess to engine braking, when I slow down using cruise control, it does activate my brake lights

Am I the only one who is surprised that Highway code stopping distances have not changed over the 40 years I have been driving, given the vast improvements in both tyres and brakes over that period

[swill453]

Am I the only one who is surprised that Highway code stopping distances have not changed over the 40 years I have been driving, given the vast improvements in both tyres and brakes over that period

I guess because there are still 40 year old cars on the road, and the HC has to cater for worst case.

Scott.