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James R. Davis
Male Administrator
17284 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 05/27/2009 :  5:21 PM Follow poster on Twitter  Join poster on Facebook as Friend  
I sure don't mind people expressing their opinions here, but when 'facts' are expressed they should be clear and unambiguous.

The Better Motorcycling blog entry cited mixes facts and concepts to arrive at its own conclusion - a misunderstanding of the facts, and a preconceived conclusion at that.

To present stopping distance charts and times is entirely inappropriate as an indication of relatively safe following distance. NOBODY (other than those like the Better Motorcycling blog who wish to 'prove' a goofy theory) claims that a 2-second following distance is in any way related to STOPPING. It is EXCLUSIVELY a distance designed to allow you to recognize a threat, decide to do something about it, and begin reacting (start braking, for example.)

Studies have made it clear that 'typical' drivers (of automobiles) take less than 1.7 seconds (thus, the use of 1.6 seconds) of PDR (Perceive, decide, React) time. What does that mean? It means that of all drivers tested, EVERY ONE OF THOSE WHO ARE IN THE BEST 70% tested, take less than 1.7 seconds. The median for those is very close to one second. By no means does it mean that 70% of all drivers take 1.7 seconds to react. Indeed, NONE of them took that long - they were ALL faster than 1.7 seconds.

The statistic for the top 50% of drivers is very close to 1 second. Again, that means that they ALL took less than 1.1 seconds to react.

If the statistic was for 100% of all drivers, it would no doubt show that ALL of them could react within ONE MINUTE, even the slow witted, marginally blind, modestly intoxicated drivers who happen to drive cars.

Motorcyclists are usually FASTER from a reaction point of view than is the population of non-motorcycling public. NEVERTHELESS, since the MEDIAN or actually, the AVERAGE, reaction time found during testing is ONE SECOND, then a TWO SECOND following distance assures that VIRTUALLY ANY RIDER can recognize a threat and begin reacting to it before they get to the point in the roadway where the preceding vehicle was at when the threat first presented itself. As Scott said, MEANWHILE, that car has moved on and is no longer at that spot in the road.

So, if the preceding car hit its brakes at point 'A' on the roadway, then if you have maintained a 2-second following distance, you will begin braking about ONE SECOND WORTH OF DISTANCE BEFORE YOU GET TO POINT 'A'. No matter how fast you are both traveling before the threat, you can do anything that leading vehicle can do before it does it - including come to a complete stop - so long as that leading vehicle remains in control (does not run into a brick wall, for example.)

Sure, you can decide to ride with a 3 second or a 4 second following distance - or even a 12 second following distance. But if you use 2 seconds you are RELATIVELY SAFE. Indeed, you are relatively safe with a following distance of anything more than ONE SECOND, and that is why that distance was doubled as a 'rule of thumb' - to make it obviously true!!!!

Any argument that fails to clearly maintain that the distance is designed MERELY as a reaction buffer is disingenuous or misinformed.
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aidanspa
Male Advanced Member
1739 Posts
[Mentor]


Omaha, NE
USA

Harley-Davidson

Road King

Posted - 05/27/2009 :  5:23 PM
quote:
Originally posted by scottrnelson

I already pointed out that the two second following distance isn't valid if whoever you're following hits a brick wall and you don't notice it's there until they hit. But two seconds is enough to notice someone in front of you making an emergency stop and to get stopped yourself before you hit them.

I'm making the assumption that you have to pay attention to what's happening in front of you for a two second distance to be safe.


I swear I'm not picking on you Scott. I am not as experienced a rider as many here, and I am simply trying to understand. It is unlikely that whomever you are following will hit a brick wall that falls from the sky, so I am hearing you say that 2 seconds is enough, pretty much always.
quote:
The two second distance applies at all times, including when starting out from a stop light or stop sign.

Certainly three or four or ten seconds of following distance would be "safer", but two seconds is good enough.

I guess I'm thinking that two seconds is a bare minimum, rather than "good enough". Since following distance is something we have control over, why wouldn't we give ourselves more than we absolutely need?


Scott & Roger - Thanks. I understand what you're saying about traffic filling a four second void. But where is the hazard in having a new vehicle now two seconds in front of you? That sounds like a comfortable following distance, and by slowing gradually or perhaps changing lanes the distance between you and a hazard could be increased if necessary.
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aidanspa
Male Advanced Member
1739 Posts
[Mentor]


Omaha, NE
USA

Harley-Davidson

Road King

Posted - 05/27/2009 :  5:31 PM
quote:
Originally posted by James R. Davis

I sure don't mind people expressing their opinions here, but when 'facts' are expressed they should be clear and unambiguous.

...

The Better Motorcycling blog entry cited mixes facts and concepts to arrive at its own conclusion - a misunderstanding of the facts, and a preconceived conclusion at that.

...

Any argument that fails to clearly maintain that the distance is designed MERELY as a reaction buffer is disingenuous or misinformed.


Jim, point taken. I shouldn't have posted the braking distance/time charts as they were not pertinent to the two second reaction discussion.
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rkfire
Advanced Member
1690 Posts


Stratford, CT
USA

Suzuki

Bandit

Peer Review: Blocked

Posted - 05/27/2009 :  5:40 PM   Join poster on Facebook as Friend  
quote:
Originally posted by Nigel A

I note your point, rkfire, but personally I wouldn't generally think in terms of the minimum safe following distance.


I don't either. I have a hard time sitting at the computer and trying to estimate my usual motorcycling distances. I think it depends on the type of road, traffic, speed, and potential for encroachment my other motorists.

I do recognize that 2, 4, or 12 seconds are somewhat of a consensus numbers to advise those that might need hard numbers.

I suspect that you'd agree that on a mulitple lane highway, while scanning far enough forwards, that a motorcyclist could easily stay 2 seconds behind the vehicle in front safely and increasing that distance with the throttle the moment you see a potential issue developing ahead. With traffic behind, a tap or 2 with the brake light as well when warranted.

I've let my guard down twice. I posted them in lessons learned category. No motorcycle safety expert here.
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gymnast
Moderator
4263 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 05/27/2009 :  5:43 PM
The concept of "slowing down to go faster" has a lot to do with adopting a pace suitable to events and their proximity in time and distance along with the added factor that their may be disparity in terms of ones familiarity with the different types of events encountered. By "going slower" in unfamiliar situations or circumstances one is able to figure more optimal solutions than when one is forced to "do thinks quick and dirty" as a result of attempting to maintain an artificially and ultimately unrealistic fast pace that greatly increases the chances of errors occuring.

The term "slow down to go faster" has applications to everything from career planing to sports. My own view is that it is always wise to to proceed at the most efficient pace and that is usually events dependent in the sense that sometimes one must react to events and sometimes you have to make something happen.

A 2 cents worth observation.
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(Deleted or Lost)

Posted - 05/27/2009 :  6:38 PM
The simple mechanics of an internet forum discussion tend to make a single subject the object of the discussion, and 'side points' tend to be seen as 'nit-picking'.
But riding a motorcycle involves multple simultaneous activities (up to 49 by some analyses), and riding a motorcycle well requires multiple simultaneous judgements in many of those simultaneous activities.
So a discussion of a minimum following distance is just that. A discussion of just one of the judgements we are making all the time.
IMO, it is well demonstrated that 2 seconds is a safe rule of thumb for a minimum following distances. The discussion of things that might affect that by requiring a longer following distance is beneficial and informative, but it is a useful discussion, not an argument against the accuracy of that basic rule of thumb.

Let's not lose sight of that...
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gymnast
Moderator
4263 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 05/27/2009 :  7:37 PM
Themeromorph. "Multiple simultaneous activities" are the norm in traffic. Excellent point. Like multiple SIPDE "loops" overlaying one another, some urgent and others emerging while still others become irrelevant as a result in a change in speed direction or relative position.
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rkfire
Advanced Member
1690 Posts


Stratford, CT
USA

Suzuki

Bandit

Peer Review: Blocked

Posted - 05/27/2009 :  7:43 PM   Join poster on Facebook as Friend  
quote:
Originally posted by aidanspa
Scott & Roger - Thanks. I understand what you're saying about traffic filling a four second void. But where is the hazard in having a new vehicle now two seconds in front of you? That sounds like a comfortable following distance, and by slowing gradually or perhaps changing lanes the distance between you and a hazard could be increased if necessary.



I'm not sure I convey my thoughts on that adequately, but I'll try. I like to control the space about me on a bike as much as possible. I don't trust the other motorists. If I can discourage changing lanes in front of me, I'd just as well they change lanes between 2 cars instead.

In the scenario you describe, and the car signalled the intent to change lanes, and he was in the middle of that 4 second space, then I have no problem with it. On the other hand, many others will do it without the turn signal, and not necessarily in the center portion of the 4 second space.

I have no problem slowing down, or speeding up for that matter, to make space for someone signalling to merge.
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rioguy
Ex-Member

Posted - 05/27/2009 :  8:12 PM
Watching the thread, I think most seem to agree that under IDEAL conditions 2 seconds is enough. Except for group riding, under IDEAL conditions, there is no need to be 2 seconds behind another car. There are times when a car will pass through a larger space, but they seldom stay there.

I did have a situation where a car appeared in front of me at a complete stop. I was in the passing lane on I-25 about 4 seconds behind a cluster bomb of tailgating cars patiently waiting for them to pass before I moved up. For some reason (I suspect a left front tire blowout) the lead car spun out. My first indication was a cloud of dust and I slowed at that indication. The first I saw the car it was pointed in my direction stopped against the guardrail. I perceived it as a car crossing the median but was still able to stop well before the car as I moved to the shoulder.

My personal preference is to work very hard to get as much space as possible.

One thing I've noticed is that if I'm maintaining a 4 or more second interval, traffic behind me seems to perceive I'm moving slower than the vehicle ahead. They move over to pass sooner to avoid getting boxed in behind me.

People overestimate how much time they gain by being in the left lane. Recently, I took a 1,020 mile ride on I 25 where the speed limit is 75 mph except through cities. My average speed over the whole distance was 70 mph while moving. I took another trip from Cincinnati, OH to Ogallah, Ne. The speed limit in Ohio was 70 mph, but through Illinois and Iowa, it was 65 mph. In Nebraska, it was 75 mph. Again a larger than 2 second following distance saved me in Nebraska. A car ahead of me slammed on his brakes and came to a complete stop in front of me for no apparent reason. It turns out he missed an exit and he backed up to it. Over a distance of 1,050 miles, my average speed while moving was 65 mph. Very close to the speed limits without speeding and while taking a relaxed attitude towards getting ahead.

There is a tip about being an elastic band in traffic. When traffic slows down rather quickly, one can slow more moderately and catch the traffic ahead. This gives the vehicle behind a better chance to stop without slamming on their brakes. This is more easily done from 4 seconds or more back than 2 seconds back.

Consider this a contrary opinion if you like. But I've never considered 2 seconds enough, even in a cage. If it occurs, I consider it transitory and do what I can to increase it. There are ways to do it and enhance traffic flow.

The only exception is when passing a car on a 2 lane road. Then I will move to 2 to 3 seconds, accelerate in my lane and pull out when I can see for sure it is clear. Even in this situation, I'll hang back more until I'm approaching a passing zone.

Here are a couple of videos I took while riding on the interstate. The first one is where it is 2 lanes, the second is through Denver. As you can see, it is generally possible to get more than 2 seconds. I don't have a video, but there are ways to get it even in rush hour traffic.

http://www.youtube.com/watch?v=q8AT...channel_page
http://www.youtube.com/watch?v=cWlx...channel_page
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James R. Davis
Male Administrator
17284 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 05/27/2009 :  8:34 PM Follow poster on Twitter  Join poster on Facebook as Friend  
quote:
Again a larger than 2 second following distance saved me in Nebraska. A car ahead of me slammed on his brakes and came to a complete stop in front of me for no apparent reason.

I think it's time that you explained such a declaration rather than have us take that on faith.

What is it that you could do with a larger than 2 second gap that you couldn't do with a 2 second gap? Surely you don't mean for us to believe that that car could stop more quickly than you could? So, unless your reaction time is longer than 2 seconds, how did having a larger gap 'save you'?

Nobody, as far as I can tell, has said that a 2 second following distance is safer or even as safe as a 3 second gap. We have said that it is a MINIMUM space that provides reasonable safety. If you think that a 3 second gap is as safe as you want it to be, then use a 3 second gap and explain to the next guy who challenges you by declaring that a 4 second gap is safer than a 3 second gap that you only meant that it was a minimum you accept as safe enough for you, and so on.

Now if someone were to advocate a 1/2 second gap, then a lot of us would climb all over him for that recommendation because it is NOT 'reasonably safe' in that despite a rider being perfectly aware of what was happening in front of him and having extremely quick reflexes and a perfectly equipped bike, the following rider could EASILY be confronted with a collision that he could not avoid.
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rioguy
Ex-Member

Posted - 05/27/2009 :  8:38 PM
James,

Consider this a somewhat contrary opinion. In the end, after more discussion I may agree.

You made the statement that motorcyclists are faster than other drivers on the average. As I recall, this statistic comes from a motorcycle show in Canada where volunteers took a reaction test. Perhaps your statistics come from another place, but I really doubt there has ever been a study where riders on the road were randomly stopped and their reactions were tested. I suspect any test was from some form of self-selected group. Buy its very nature, a test improves reaction time so we can never know the reaction time of the average rider on the road not taking a test.

Riders are also prone to using their brakes incorrectly. Many riders have "laid it down to avoid a crash" when in reality they misused their brakes. There are still a lot of riders around who don't use the front brake and some who don't use the rear brake.

In very dense traffic, I can see where one might be forced to use a 2 second following distance. Perhaps avoiding these situations is appropriate. I understand your environment is different than mine and perhaps you have adjusted to 2 seconds. With your skill level I have no problem with that. But for the person who generally doesn't ride in those conditions, I feel striving for only 2 seconds isn't enough. Personally, I'll keep fighting for more.

I found this articles from Reuters which is a reprint from a company called "Drivecam." The studied 17 million events.

"Although recommended following distances can vary by weight
and size of vehicle, most nationally recognized driver training
programs advocate a minimum following distance of three or four
seconds. "

Drivecam is run by American Family Insurance and promotes behavior based improvements in safety. I find this page quite interesting:

"http://www.teensafedriver.com/overview.htm"

They put a cam on the mirror and then send the videos to an analysis center.

"The Teen Safe Driver Program uses a small device placed behind the rearview mirror of your teens vehicle. It captures the view out the front, and into the interior, of the vehicle but never saves any data UNLESS activated by an erratic vehicle movement extreme braking, cornering, and acceleration or if there is a collision. When the device is activated, it saves an EVENT comprised of the previous ten seconds and the following ten seconds showing not only WHAT happened but WHY it happened.

The event is transferred wirelessly to DriveCams Event Analysis Center where the video is reviewed, scored and coaching tips are added. Parents and teens log in to a secure Web site to view the video and tips for safer driving. Teens are coached for improvement in problem areas, and also praised for good driving events."

I'd love to have a device like this on my bike.

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James R. Davis
Male Administrator
17284 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 05/27/2009 :  8:42 PM Follow poster on Twitter  Join poster on Facebook as Friend  
quote:
Again a larger than 2 second following distance saved me in Nebraska. A car ahead of me slammed on his brakes and came to a complete stop in front of me for no apparent reason.

I think it's time that you explained such a declaration rather than have us take that on faith.

What is it that you could do with a larger than 2 second gap that you couldn't do with a 2 second gap? How did having a greater than 2 second gap 'save you'?
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rioguy
Ex-Member

Posted - 05/27/2009 :  8:58 PM
"I think it's time that you explained such a declaration rather than have us take that on faith. What is it that you could do with a larger than 2 second gap that you couldn't do with a 2 second gap?"

Casual braking rather than something approaching threshold braking. Let me explain.

If a car is proceeding down the interstate at a normal speed and there is no traffic in front of him, there is no reason to suspect he will suddenly use something approaching threshold braking. At 2 seconds, when the brake lights come on I might suspect just normal slowing down. It would take time to realize my overtake was too much and then transition to threshold braking. At that point, I would have the equivalent of less than 2 seconds spacing. According to www.drivecam.com 47% of rear end collisions occur with less than 2 second spacing. 36% occur when a vehicle comes to a complete stop. I'd have NEEDLESSLY been in a situation where 83% of the rear end collisions occur. (36% depending on how it's calculated.) Why would one put themselves in that situation when not in dense traffic? There was plenty of opportunity to have a ton of spacing and using it perhaps prevented a scary situation.

Let's say I was at 2 seconds and I started braking 1 second after. Yes, I would probably have been able to stop in time. But what about the guy behind me? Because I was casually braking, I had time to scan for traffic behind me and choose an option to go either left to the left lane or right to the shoulder. Right was my second choice as I didn't know if the guy would pull to the right. As it turned out, there was no traffic behind me and I went around the left very slowly.

I do try to avoid declaratory statements. I should have said something like "I feel..." To avoid confusion I won't go back and change it now unless you'd like me too and I'll annotate the change.
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rkfire
Advanced Member
1690 Posts


Stratford, CT
USA

Suzuki

Bandit

Peer Review: Blocked

Posted - 05/27/2009 :  9:13 PM   Join poster on Facebook as Friend  
quote:
Originally posted by rioguy

The only exception is when passing a car on a 2 lane road. Then I will move to 2 to 3 seconds, accelerate in my lane and pull out when I can see for sure it is clear. Even in this situation, I'll hang back more until I'm approaching a passing zone.





I don't pass like that either. I think getting a flying start to a pass puts you in a situation where the go/no go point is further back and at higher speed. But again, different geography has a lot to do with it. You've got some wide open spaces where you can see ahead for miles. I've got shorter straights, with shorter passing zones.

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Axiom2000
Male Moderator
1761 Posts
[Mentor]


Georgetown, Delaware
USA

BMW

F 800 GT

Posted - 05/27/2009 :  9:31 PM
Maybe not exactly on point, but today I had to make a 80 mile round trip on my motorcycle. It was mostly 4 lane divided highway. While riding I got to thinking about this thread. I soon realised that I selected my following distance on what felt safe and comfortable. I noticed that I would speed up or slow down to maintain that perceived safe distance. Funny thing is, I checked it at numerous times during the trip and it was almost always 2 seconds.
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rioguy
Ex-Member

Posted - 05/27/2009 :  9:33 PM
quote:
Originally posted by rkfire

quote:
Originally posted by rioguy

The only exception is when passing a car on a 2 lane road. Then I will move to 2 to 3 seconds, accelerate in my lane and pull out when I can see for sure it is clear. Even in this situation, I'll hang back more until I'm approaching a passing zone.





I don't pass like that either. I think getting a flying start to a pass puts you in a situation where the go/no go point is further back and at higher speed. But again, different geography has a lot to do with it. You've got some wide open spaces where you can see ahead for miles. I've got shorter straights, with shorter passing zones.




This is interesting. Two contrary threads going at once. I've never seen you pass, so I can't comment.

I developed this method of passing as I've always driven small cars with small engines. I've found it is very efficient. On a wide open road, passing is similar to an interstate pass, just a little faster. Consider this an area with restricted visibility.

If I hang back 2 or 3 seconds, I start to accelerate as I come out of a curve and suspect there will be an opportunity to pass. If it's not clear, I just slow and reestablish my spacing. If it is clear, I've already done most of the acceleration in my own lane and I can go right around.

By hanging back farther, it gives me a better opportunity to examine the road ahead for things like cross traffic and deer because I'm not quite as vulnerable if the person ahead of me slows. I'm still in a much better position than those who try to pass from a tailgating position and accelerate after they pull into the opposite lane.

The time you are at a disadvantage is if there is a vehicle behind. Then you have to be careful they don't decide to pass you while you pull out.

Yes, this method does take practice and careful attention. But it minimizes the time one spends in the opposite lane. (For those with high powered bikes, I can see doing it differently.)
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James R. Davis
Male Administrator
17284 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 05/27/2009 :  9:34 PM Follow poster on Twitter  Join poster on Facebook as Friend  
Rioguy,

Once again the thread has wandered into a tangent. The 2 second rule is not in place to account for your misjudgements of a threat or for failing to stop as quickly as someone else, it is ENTIRELY a reaction time buffer.

While stopping, if you notice that the car ahead of you is slowing faster than you thought it was, you squeeze harder. That PDR time is in tenths of a second, not anywhere near the 'extra' second already built into the 2 second rule.
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gymnast
Moderator
4263 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 05/27/2009 :  10:03 PM
An aside. I think that some of the confusion attendant to "the 2 second rule comes from why and when it was developed. Up until the 1960s drivers handbooks and driver education materials stressed the "One Car length following distance for each 10 MPG of vehicle length". Because of the difficulty estimating "car Lengths", variously described as being from 16 to 20 feet, it was determined that the "2 second following distance was much easier to comprehend, teach and implement. I must be remembered that at the start of the 1960s vehicles did not have anti lock brakes and it was difficult for the average driver to obtain .9 or higher g levels during braking without locking the wheels and the pumping of brakes to prevent wheel lockup was stressed. Today, with high performance tires and antilock brakes virtually any driver can obtain dry road g levels of .9 or better simply by forcefully pressing the pedal. The avarage motorcyclist can not, in my opinion obtain braking g level above .7 unless they are practiced.

About 15 years ago some of the driver education materials began to suggest a 3 second following distance to reflect the greater g levels that could be obtained with the newer vehicles with antilock brakes and high performance tires. Some cars have much better braking capability than others and most drivers can stop their cars in a far shorter distance than a large percentage of motorcycle riders.

The practical problem for all careful drivers is that in urban traffic densities on multi lane roads, other drivers will quickly move into the gap. One additional point is that drivers using a two second following distance are likely using other perceptual skills and all to the good when it comes to minimizing risk. The problem is drivers that use a less than 2 second following distance, while dialing a cell phone and using the hood of the car a as a central visual reference point. Motorcyclists running less than two second following distances are primarily a hazard to themselves rather than being a "general public health hazard".

Edited by - gymnast on 05/27/2009 10:11 PM
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(Deleted or Lost)

Posted - 05/27/2009 :  10:28 PM
*&@%$#@, Gymnast!

I wanted to keep this bike for ever!

You've just convinced me I need to get an ABS equipped bike!

I love my current bike! May your ears rot and drop off!
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James R. Davis
Male Administrator
17284 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 05/27/2009 :  10:34 PM Follow poster on Twitter  Join poster on Facebook as Friend  
quote:
About 15 years ago some of the driver education materials began to suggest a 3 second following distance to reflect the greater g levels that could be obtained with the newer vehicles with antilock brakes and high performance tires. Some cars have much better braking capability than others and most drivers can stop their cars in a far shorter distance than a large percentage of motorcycle riders.


That is the strongest argument I've heard so far for using a 3 second following distance instead of a 2 second distance.

Your assertion that most motorcyclists can't get over a 0.7g deceleration rate is plausible, though my belief is that almost any experienced motorcyclist can actually get closer to 0.8g's. (You will recall that a rank amateur who had ZERO riding experience before taking the BRC is tested to see that they can attain at least a 0.6g deceleration rate.) But in any event, let's look at the extremes. At 70 mph, a vehicle that attains a deceleration rate of 0.9g's takes almost exactly 1 second less time to stop than one that attains a deceleration rate of 0.7g's (3.5 seconds instead of 4.5 seconds). Any slower speed, or better performance by a motorcyclist cuts away at that 1 second difference. So, if a motorcyclist's PDR is about 1 second, then in THE WORST CASE scenario described above, with a 2 second following distance the two vehicles could impact when they were both traveling at about ZERO mph while in the vast majority of cases the motorcyclist would still stop before the car does.

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