Team-BHP - Driving Guide : Rules, Tips, Etiquette & Common Mistakes To Avoid

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Originally Posted by NomadSK (Post 5712448)

So you made me scratch my head. Your analogy is correct as long as you are comparing it with the fixed object with zero velocity. But the 2-second rule or whatever second rule is with respect to the relative speed of the vehicle being followed. It’s a thumb rule at any relative speed (technically which should be zero) have the tailing and following car.

Only problem I can see is, if car A comes to an abrupt halt (0 speed in 0m distance) by colliding with a rigid concrete wall, then your logic of 2 second being insufficient holds good. That’s not an ideal scenario though.

Generally it’s a rule in normal driving conditions, adverse weather conditions will require more time frame (gap) for safe driving.

Well for defensive driving you need to prepare not for the "normal" but abnormal. Here are some scenarios that you might want to consider

1. The car you are following has a tyre burst.

2. For some reason there is a visibility problem, a curve where an idiot has parked or the is a wild animal or the holy cow etc

3. In any scenario where the car in front has "superior braking" (technically infinite). This "braking" can be "achieved" by rear ending another car, bursting ones tyre or any of the numerous "techniques" that we Indian drivers are well versed with.

I think you really need to think of the car in front as a something that can metamorphosis into a brick wall at any point in time. If that is your model of the car in front what I said is the inescapable conclusion.

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Originally Posted by tilt (Post 5712547)

Er... I believe you're conflating distance with time. The two seconds is time and is not supposed to be calculated into a distance.

No I am not conflating distance with time. If you are following the 2 sec rule (say rather strictly) then at any point of time the distance between you and the car in front is proportional to your speed (speed * 2 ). I am objecting to this rule.

Modified 2 sec rule

Here is how I think two sec rule should be implemented in practice.

1. Set a threshold speed say 40 kmph below which you are comfortable with using the 2-sec rule. I will call this the 2-sec threshold.

2. For every 40 kmph additional speed add 2-sec to your the "following time". This can be summarize as follows

2.1 Till you hit 40 kmph follow 2 sec rule
2.2 Between 40 to 80 follow 4 sec rule. Or say 40-60 (3sec) and 60-80 (4sec)
2.3 Between 80 to 120 follow 8 sec rule
2.4 Beyond 120, you should not be driving on any roads in India

In practice you might want to have a different threshold. May be due to slippery roads or you are driving a heavy vehicle or you are growing old and do not want to trust your reflexes too much (case in point me). Then you may choose a lower 2-sec threshold. Say you choose 20kmph as your 2sec threshold. Then for every 20 kmph increase your "following time" by 2 secs. As with the usual two sec rule, you will need to adjust your following time depending on the hazard. In our case it amounts to lowering the 2-sec threshold.

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Originally Posted by electric_eel (Post 5713135)

1. The car you are following has a tyre burst.

Even if the car in front will have a tyre burst, it won't come to complete halt. That's why 2 second rule is there to invade such abrupt scenarios to take evasive actions.

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2. For some reason there is a visibility problem, a curve where an idiot has parked or the is a wild animal or the holy cow etc

As in my previous statement, 2-Sec rule isn't for adverse weather condition. Also this rule is for 2 vehicles in motion (with zero relative speed) and not one among them stationary.

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3. In any scenario where the car in front has "superior braking" (technically infinite).

Now this is an hypothetical situation. How would any-sec rule behave if the car in front reverses and front ends you ? I don't think its possible to have solutions for all arbitrary situations.

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I think you really need to think of the car in front as a something that can metamorphosis into a brick wall at any point in time.

If I will think in that direction, then I would be safe in a stationary car and wont be able to drive it on the roads

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It's a MINIMUM 2-second rule, cardinal sin to break this, specially on expressways where high speed traffic is encountered as Consequences can be severe. If somehow one isn't comfortable in maintaining that, the person can always increase the gap with which he's comfortable.

Traffic/Safety engineers have some general guidelines they have developed over the years and hold now as standards and Min 2-Sec rule is among them.

Quote:

Originally Posted by NomadSK (Post 5713264)

Even if the car in front will have a tyre burst, it won't come to complete halt. That's why 2 second rule is there to invade such abrupt scenarios to take evasive actions.

[snip]

Traffic/Safety engineers have some general guidelines they have developed over the years and hold now as standards and Min 2-Sec rule is among them.

The only point I am making is that one needs to understand the assumption behind 2-sec rule : "normal driving" where every one is braking and following the 2 sec rule. It also gives people a reasonable rule of thumb which is easy to implement in their daily life. Unfortunately I think it is not good enough for a defensive driver more so in India.

My modified 2 sec rule was my (feeble) attempt at getting to a simple rule for the defensive driver which I think is better justified than the base 2sec rule (or 3sec rule or k-sec rule; the numbers do not matter what matters is the principle).

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Originally Posted by electric_eel (Post 5713135)

Modified 2 sec rule

Needless to say I am not advocating "blind following 2-sec rule" while ignoring the other aspect of defensive driving like anticipation etc. Also I do understand that it is MIN 2-sec not max. It would be absurd for me to suggest that if the distance between the car is greater than 2 sec then speed up and close the gap.

Guys, let us stop knocking our heads against the theory and the rules of thumb. What matters is to keep enough distance. All I can say is, when you think it is enough, increase it. And if someone is tailgating you, double it: you need stopping distance for two.

I know, in most cases it is physically impossible for the car in front to come to an instant halt. But it is not impossible for it to almost-instantly lose a lot of speed with heavy braking. Pretty sure that is the story of my last rear-ending: I didn't stop, but had to brake very sharply, and the guy behind me couldn't match that.

Let me tell my two-second rule: For two seconds, meditate on the sound of breaking glass and scrunching metal. I find this works wonders at moderating my driving! rl:

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Originally Posted by Thad E Ginathom (Post 5713338)

Guys, let us stop knocking our heads against the theory and the rules of thumb.

Can't help it. Does it for a living actually :D.

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I know, in most cases it is physically impossible for the car in front to come to an instant halt. But it is not impossible for it to almost-instantly lose a lot of speed with heavy braking. Pretty sure that is the story of my last rear-ending: I didn't stop, but had to brake very sharply, and the guy behind me couldn't match that.

Same with me. Not just once but 1 1/2 times.

1. I anticipated, braked rather smoothly and yet was rear-ended (ever so slightly) by a truck. A very minor tailgate deformation (even the rear camera was working) but had to
leave our month old car at the body shop for about 2 weeks.

2. Almost got rear ended by a brezza (caught on dash cam). Again braked very smoothly.

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Let me tell my two-second rule: For two seconds, meditate on the sound of breaking glass and scrunching metal. I find this works wonders at moderating my driving! rl:

Nothing beats this 2 sec rule for sure.