Talk:Two-second rule

Diagram
I'm not real happy with the diagram associated with this page. I've always been taught that I should have two seconds of distance between the rear of the car ahead of me. The diagram shows the distance measured between the fronts of both vehicles. --Ansible 19:15, 26 September 2006 (UTC)
 * Good point. I always heard it should be the back of car A vs the front of car B. Besides, the person in car B can't really even see the front of car A. (At highway speeds, I guess it may be not an issue, as the text is generic, talking about when the car passes the tree or whatever.) Fan-1967 19:17, 26 September 2006 (UTC)

perspective and accuracy
how does the driver estimate accurately when the rear end of the car in front passed the mailbox? it is far more difficult from his perspective, than from, say, someone standing on the side of the road opposite the mailbox (at right angles to the front of the car)? --ti 22:35, 4 December 2006 (UTC)

Two seconds?
In Sweden, drivers are learned to count to three, not two, which is called the three second rule. Does this article really apply worldwide? It feels like this is mostly facts from Ireland and the US. Grinder0-0 18:21, 19 April 2007 (UTC)


 * Two second rule is prevalent in the UK, used with the saying "Only a fool breaks the two second rule" which takes two seconds to say in normal speech tempo.

https://www.youtube.com/watch?v=f481xKNN8YQ https://www.youtube.com/watch?v=mf5d2DP4Pp0 — Preceding unsigned comment added by 77.86.117.208 (talk) 08:28, 27 April 2018 (UTC)

In Northern Virginia in the USA we're taught to count to three as well.....two seconds isn't enough !68.33.190.196 22:35, 3 June 2007 (UTC)

I was taught four in Wisconsin 24.196.81.209 12:38, 8 June 2007 (UTC)


 * Interesting, maybe this article could be merged into something, I don't know what yet. Grinder0-0 21:03, 26 September 2007 (UTC)


 * Yes, the article should be renamed and moved to "Three-second rule". -USA  Mikiemike (talk) 23:58, 8 August 2009 (UTC)


 * Two seconds is simply not enough and continuing to promote this value will lead to hundreds if not thousands of avoidable collisions. Race car drivers on dry pavement under ideal conditions of visibility and concentration might, just might, get by with two seconds.  An additional second is necessary for focus to be brought back to the road.  That insurance company ad citing two seconds is simply criminally poor advice. [User:wildcatherder]  — Preceding unsigned comment added by 71.93.61.138 (talk) 01:06, 28 December 2012 (UTC)


 * The Washington Driver's Manual says, "To tell if you are driving too fast for conditions, use the Four-Second Sight Distance Rule." I haven't heard a "Two-Second Rule" in many years.  — Preceding unsigned comment added by 67.185.161.246 (talk) 20:45, 21 December 2013 (UTC)

In or out of the city?
The 2 second rule is based on the needed time: for driver's assesment and decision (half second or more), reaction (0.2-0.4s), technical reaction of the car brake system to effective start of killing the speed (0.1-0.3s), + some reserve and thus is more or less correct. Especially if you never watch the situation if front of the front cars, but just keep an eye on that car's rear to eventually start braking.

Still in the heavy traffic of the cities the rule is impractical and usually disregarded. Typical speeds there are 30 to 80 km/h (20-50 mph) respectively requiring "2 second distances" of 15-45 m (50-150') or 3 to 10 "car lengths". Following such a rule rases problems: 1. You will have to slow down all the time to maintain distance, becoming an obstacle to the rest of the traffic behind pushing them all to risky overtakes; 2. The drivers in the other lanes will consider the room in front of you a "free place" as you obviously have some technical or personal problem to keep with the normal traffic and will tend to make abrupt three lane changes, turn switches, U-turns and even right side overtakes as on an empty road; 3. Cars from the side streets will most probably enter the lane or cross the road just in front of you and so will do the crossing pedestrians, the bicyclists and everybody else.

Here in Bulgaria the preffered distances are 1 or 2 "seconds" out of cities and 1-3 "car lengths" (15-50') in the traffic ! Again, every driver attentively watches the road far forward (at least 2-3 cars or more forward) to have the needed time for adequate reaction ! before the next front car started braking!

Or - as it often is - go with the rest and do what most people do - be predictable to other drivers. Rules are general approximations (usually too general and too approximate) while truth and adequacy are always very concreate and multifactored. So rules are OK when you can't or prefer not to asses the situation in real, but better if you could learn to - it's safer then rules.

Ivo Kisselov, Sofia Bulgaria 89.215.216.25 09:48, 18 August 2007 (UTC)

Current U.S.A. practice is 3 seconds, 4 in rain, 7 in ice & snow 3/11/2010 --

Human Psychology and social issues of a safe following distance
Ivo Kisselov, I think your assessment is a bit excessive, but generally you raise what I believe are some very common and relevant issues. The driver behavior here in the US is very similar to what you described. This leads me to believe that the response is an issue of human psychology more than an and issue of nationality or anything else. Education in the form of safety training and advanced driver training is needed to change these ways. Keep in mind that the worst-case driving scenario of someone else, does not mean that it is more safe for you to drive recklessly to match that driver's behavior and attitude.

1. There's nothing really wrong with slowing down. It decreases the chance of an accident, that's the whole point.

Whenever you're feeling stress from driving, 9 times out of 10 the safest thing to do is slow down.

2. It's just a fact of life that aggressive and ignorant drivers will cut you off, whether the space in front of you is large or small. It's safer when it's a larger space. Your sense of losing your place in line is purely emotional and social. I see no basis in reality for it, do you? What's your hurry? Why do you care if it takes a second longer to get where you're going? So slow down, and get to where you're going 2 seconds later, and alive rather than dead.

3. More time is wasted by traffic backups from accidents than is saved by narrowing the gap from 2 seconds to 1 second. You should really try 3 seconds for awhile, then switch to 2 seconds and it won't seem like much.

Leaving a 2 second gap is not unpredictable. The only thing that's unpredictable is to drive haphazardly, and do those dangerous maneuvers you mentioned.

Just because everyone else drives like a manic doesn't mean it's correct or safe. If they jumped off a bridge, would you? I agree, the 2 second rule takes a lot of getting used to, but it's the right way to drive. Someone has to set a good example. Even if only 1 out of 4 people used it, then it wouldn't seem so strange. So tell your friends and family and the roads will be a little safer.

We need a section in the article discussing this social/psychological issue. Mikiemike (talk) 08:14, 22 February 2008 (UTC)--

Use of Vehicle Lengths as a Guide
Near the beginning of the article it explains the two second rule as, basically, keeping the distance between the front of your vehicle, and the rear of the one you're following, to at least the distance that you travel in 2 seconds. This makes perfect sense. However, the article then goes on to say that this equates to one vehicle length for each 5mph / 8kmph of speed. This latter statement is complete nonsense. The reason I say this is because the distance travelled in 2 seconds is dependent only on speed and has nothing whatsoever to do with vehicle length. For example, if you are driving at 60mph, then that equates to 88 feet/second, so in 2 seconds you travel 176 feet, and that is true irrespective of whether you are driving a short car or a long lorry. The bit about vehicle lengths should therefore be deleted. Snookerrobot. Snookerrobot (talk) 20:32, 8 August 2009 (UTC)


 * "Vehicle lengths" as a unit are generally only used in guides for passenger car drivers. Other rules of thumb that appear in trucker guides actually factor in the length of the truck as a general estimate of its weight and stopping distance.  The whole thing is silly because stopping distance squares with speed, and people should really be doing something like counting half a second for every 10mph they are traveling, with the fact that drivers ahead of you rarely encounter a brick wall in the middle of the highway making up for the delay caused by reaction time.  However it has been shown time and time again that the general population cannot understand quadratics, and at least "second rules" help them increase distance at higher speeds.(140.232.0.70 (talk) 20:21, 28 May 2013 (UTC))

out of date, inaccurate, and simplistic
Many organizations in the USA and some national and state publications now recommend the 3-second rule under normal driving conditions. See AARP, AAA, National Safety Council, Beacon Mutual.

Also, if you compare actual stopping distances with the recommendation of the 3-second rule, you find that stopping distance increases faster than linearly with speed, so even the 3-second rule will not prevent multi-car collisions if the lead car stops more suddenly than just applying brakes.Wcmead3 (talk) 20:35, 21 January 2012 (UTC)wcmead3

Doubling
In the UK, as taught by my driving instructor, so sorry no source; this rule of thumb calls for the doubling in rain to 4 seconds and doubled again in ice or snow to 8 seconds. — Preceding unsigned comment added by 77.86.117.208 (talk) 09:01, 28 February 2018 (UTC)

Equation
The third paragraph contains the equation (BD = (SMPH/20)*SMPH), but the terms aren't defined. My guess is that BD = braking distance and SMPH = speed in miles per hour. However, the US Customary equation for braking distance on the Stopping sight distance page &mdash; which I'm able to derive from the Equations of motion &mdash; when using the given acceleration of 11.2 ft/s^2 would simplify to (BD = (SMPH/10)*SMPH) since 1.075/11.2 is roughly equal to 1/10. I presume a Metric version of the equation would also be desirable. Msramming (talk) 21:44, 25 October 2019 (UTC)

# of "Seconds" rule vs. # of "Cars" rule
In driver's ed back in 2009, I was taught the # of car lengths rule. Only recently, did someone point out that this is outdated, and after swapping, I feel like they're right. I am curious on a in depth analysis between the two method, and if the # of cars rule is outdated

From what I have gathered, and from my own experience, it boils down to this:

When especially dealing with high speeds, the Seconds rule is more accurate and simple, purely due to the fact that we cannot accurately measure the # of cars in between. We might think we can. We might have lucky guesses. But guesses aren't that accurate. You also have to decide what car type to pick for the measurement. So I think there are too many variables

Now, Seconds rule isn't 100% accurate either, but no method will be unless you have some sort of advanced distance detection tech in your car - which will most likely be based on # of seconds, not # of cars.

The Cars rule can work well enough at low speeds, like 40 or below. But I don't think the low speeds are the primary concern. Either method can work for that. But we want to be consistent and use a method that is easy to learn and teach. Drivers can be tired, angry, sad, lightheaded, have a headache, tired eyes, and so on.

So, what do you think are the key points in the differences between these 2 methods, if one is more accurate and why, and if one is outdated and why? Are there any statistics and data taken from drivers that correlate to the different methods, to show that one is superior over the other? 72.68.66.100 (talk) 04:32, 29 December 2021 (UTC)