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View Poll Results: Do you think Pittsburgh drivers are extra timid in the rain?
No, people drive just as timid in the rain in my previous location. 18 50.00%
YES! What is wrong with people? Keep good tires on your auto, leave sufficient space, and just keep driving!* It's not hard! 18 50.00%
Voters: 36. You may not vote on this poll

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Old 11-15-2011, 10:17 AM
 
Location: somewhere near Pittsburgh, PA
1,313 posts, read 2,055,546 times
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Quote:
Originally Posted by Caladium View Post
Yup, this is one of those amusing things you realize when you hop around the other forums in city-data. Just about every forum has people who complain about the same things--and they all claim their city has the worst drivers of all.
Yes, there are bad drivers everywhere. And everytime a thread like this comes up it inevitably ends up with people saying "it's not just Pittsburgh!" while completely ignoring the specific complaints that were brought up that are unique to this area. Please name a place ANYWHERE ELSE where you have seen people come to a complete stop in a travel lane to allow someone to make a left turn in front of them. And I'm not talking about the Pittsburgh left. And the stopping while merging issue isn't a problem you see in many other cities.

While these threads are often like beating a dead horse, they are good for newcomers to read so they will know the UNIQUE hazards they may face on Pittsburgh roads. Whether you choose to acknowledge it or not, there are odd local driver behaviors here that people from other areas might have never seen before and arent prepared for.
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Old 11-15-2011, 10:25 AM
 
20,274 posts, read 18,712,700 times
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Quote:
Originally Posted by ditchdigger View Post
I say that if you're in the left lane, pass one vehicle, and are going to pass another vehicle that's any closer than that to the one you've just passed, you're creating more of a hazard by changing back into the right hand lane.
I agree, assuming you will be doing that at a reasonable relative pace. If it is going to take you three hours to get to the next car in line, I would suggest a different answer.

Generally, there are many accidents caused by people initially impacting the car travelling right next to them. Off hand I don't know how many relative to tailgating accidents and such, but it is enough to try to avoid riding right next to people for extended periods. Of course you don't want to whip by people either, but you should try to maintain a nice moderate passing pace.

Quote:
And for the same reason, it's not always practical for somebody in the right lane to move left and allow somebody else room to merge. If there's a 100 foot long opening in the left lane, do you really expect me to move left and reduce that spacing to 40 feet, bumper to bumper to bumper, between me and the other two guys in the left lane?
No, but you should be willing to temporarily compromise somewhat on ordinary spacing to allow in merging traffic.
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Old 11-15-2011, 10:32 AM
 
9,856 posts, read 7,820,848 times
Reputation: 5319
Quote:
Originally Posted by ML North View Post
Within the given assumptions, absolutely. Now whether those assumptions (namely a space cushion of 3 seconds at 55mph or 243 feet) are appropriate in all situations is a different discussion. But regardless of what those assumptions are the results will show that slowing down in the rain makes sense, which is painfully obvious, but nonetheless a point that you argued against earlier in this thread.

You should at least recognize the fact that sample calculation is based on reasonable assumptions, and it illustrates the point that your original argument (copied below) is demonstrably wrong.
And you should realize in physics that there is a difference between static and kinetic friction...
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Old 11-15-2011, 10:49 AM
 
5,453 posts, read 3,978,919 times
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Hahahahaa...you should see what they do in Florida!! a few drops, and every road is a parking lot! I don't get it. YES, It says in the driving manual that IF the road conditions are not optimal, the speed limit should be lowered, but it doesn't say to lower it to 10 miles an hour!

The day doesn't get longer when it rains, so we have to go where we have to go in the same amount of time regardless!
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Old 11-15-2011, 10:49 AM
 
20,274 posts, read 18,712,700 times
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Quote:
Originally Posted by hnsq View Post
Thank you both for ignoring the point I was trying to make and overly complicating an issue (like usual). I never said "NEVER SLOW DOWN IN THE RAIN".
I don't want to go back and rehash everything, so I will boil it down to a relative simple point: even if it isn't raining hard (or at all) at the moment, if the road surface is wet you should realized your braking distances has roughly doubled, and take appropriate precautions.

If you are no longer disputing that point, then fine.

Quote:
The effects of friction on a road when there is no standing water (regardless of being wet or not) is much less than your calculations have shown.
But of course you are disputing that simple point, and what you are claiming isn't true. The one link I provided explained what is going on, and the upshot is all you need is "a lubricating film of water between the tire and the road" to reduce the coefficient of friction to the stated values:

Physics 101 Tire Friction

Now it is true that standing water makes things even worse. But that is because you now face the risk of hydroplaning. In hydroplaning, your tires lose contact with the road surface entirely, and that is much worse than simply having a lower coefficient of friction.

But I am glad you admit you are in fact giving advice based on your understanding of the physics. It just turns out your understanding of the physics is wrong, which is why it is worth addressing so that people can understand why your advice is mistaken.

Quote:
ML North - I am supposed to take you seriously when the top speed in your calculations on a dry road are 68mph?
Sure, given the assumed safe spacing. To put it the other way around, people have calculated that safe spacing distance based on the assumption you will be travelling around that fast.

Quote:
Think for a second before posting!
Indeed!

Quote:
And Brian - if you actually read about the decreasing coefficient of friction (the .4 you refer to), you would know that the coefficient only decreases significantly if your tires lock. If your tires do not lock, the negative effect is negligible.
That's just wrong. Again, read the link above--that is all about the loss of friction when the tires are still rolling.

Once again, though, you are inadvertently raising a good issue. If your tires do lock, you are suddenly in MUCH worse shape in wet conditions. In dry conditions, locked tires are only slightly less effective at braking as unlocked tires. Wet tires, on the other hand, will experience a further dramatic decrease in friction. Here is someone who goes into that issue (estimating locked tires on a wet road could drop as low as 0.1 from the already lower 0.4 for rolling tires on wet roads):

Friction and Automobile Tires

Quote:
If you want to get into physics, then fine. Lets do so . . .
I actually don't want to ARGUE physics with you, and here is why. I am citing actual physics professors discussing these issues. I'm afraid that if we instead try to argue about this in a usual Internet forum way, people might get the impression there is some doubt about the subject.

In fact, there is not, and this is one of the few cases where I am going to suggest people accept an argument from authority: please listen to the physicists, and not a random Internet poster. Because this issue is too important on a direct, personal level for people to be left in doubt about what is right.
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Old 11-15-2011, 10:58 AM
 
20,274 posts, read 18,712,700 times
Reputation: 2827
Quote:
Originally Posted by Mugatu View Post
While these threads are often like beating a dead horse, they are good for newcomers to read so they will know the UNIQUE hazards they may face on Pittsburgh roads. Whether you choose to acknowledge it or not, there are odd local driver behaviors here that people from other areas might have never seen before and arent prepared for.
This seems like an excellent point to me (being a pragmatist). The endless debates about the alleged character failings of natives is pointless, but accurately describing local driving norms serves a valuable purpose. I for one will try to keep that distinction in mind.
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Old 11-15-2011, 10:59 AM
 
Location: Wilkinsburg
1,661 posts, read 1,311,663 times
Reputation: 962
Quote:
Originally Posted by hnsq View Post
And you should realize in physics that there is a difference between static and kinetic friction...
Yes, I do know the difference, so much so that I know you're using them incorrectly.

A coefficient a static friction is used to calculate the amount of force necessary to put an body in motion starting from rest. A coefficient of kinetic friction is used to calculate the reactive frictional force when a body is in motion. The numbers used in my calculations are coefficients of kinetic friction.

Perhaps you're thinking of rolling resistance (coefficient of rolling friction)? That also is irrelevant.

Anti-lock brakes work by rapidly cycling the brake calipers such that a driver can maintain steering and avoid a continuous skid, which allows the car to come to a more controlled stop in a shorter distance. When a caliper is engaged on the rotor, the wheel will either be locked for a very short period of time, or incredibly close to being locked, such that the angular velocity of the tire is negligible and linear velocity between the bottom of the tire and road is large.

Therefore, a coefficient of kinetic sliding friction is the appropriate value for this calculation, rolling resistance is negligible, and the coefficient of static friction is irrelevant.
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Old 11-15-2011, 11:35 AM
 
9,856 posts, read 7,820,848 times
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Quote:
Originally Posted by ML North View Post
Yes, I do know the difference, so much so that I know you're using them incorrectly.

A coefficient a static friction is used to calculate the amount of force necessary to put an body in motion starting from rest. A coefficient of kinetic friction is used to calculate the reactive frictional force when a body is in motion. The numbers used in my calculations are coefficients of kinetic friction.

Perhaps you're thinking of rolling resistance (coefficient of rolling friction)? That also is irrelevant.

Anti-lock brakes work by rapidly cycling the brake calipers such that a driver can maintain steering and avoid a continuous skid, which allows the car to come to a more controlled stop in a shorter distance. When a caliper is engaged on the rotor, the wheel will either be locked for a very short period of time, or incredibly close to being locked, such that the angular velocity of the tire is negligible and linear velocity between the bottom of the tire and road is large.

Therefore, a coefficient of kinetic sliding friction is the appropriate value for this calculation, rolling resistance is negligible, and the coefficient of static friction is irrelevant.
The issue is point at which you lose breaking force when your tires lock and slide. In the case of an emergency, where does the act of breaking suffer? The answer to this question is such that as a person increases force on a brake pedal, there is a point at which static friction exceeds kinetic, thus causing a car to lose control. That point is lower assuming a tire is locked, and there is no standing water.

Now do you really want to discuss physics, or can we talk about how stupid it is to drive 55 on the parkway when there is a light drizzle, like Pittsburgh drivers do every time it rains?


Quote:
Originally Posted by BrianTH View Post
I don't want to go back and rehash everything, so I will boil it down to a relative simple point: even if it isn't raining hard (or at all) at the moment, if the road surface is wet you should realized your braking distances has roughly doubled, and take appropriate precautions.

If you are no longer disputing that point, then fine.
I never once said you should maintain the same following distance. Don't put words in my mouth. I said there is no need to slow down.

Quote:
But of course you are disputing that simple point, and what you are claiming isn't true. The one link I provided explained what is going on, and the upshot is all you need is "a lubricating film of water between the tire and the road" to reduce the coefficient of friction to the stated values:

Physics 101 Tire Friction

Now it is true that standing water makes things even worse. But that is because you now face the risk of hydroplaning. In hydroplaning, your tires lose contact with the road surface entirely, and that is much worse than simply having a lower coefficient of friction.

But I am glad you admit you are in fact giving advice based on your understanding of the physics. It just turns out your understanding of the physics is wrong, which is why it is worth addressing so that people can understand why your advice is mistaken.
But you are (yet again) completely missing the point. You are (yet again) focusing so much on one tiny detail that you miss the point altogether. Obviously there is less friction on wet roads. How many times do I have to say that? In my scenario (70mph in a light drizzle), you are in no more danger of losing control than you are on a dry road. I refuse to do something as absurd as perform mathematical calculations when we are flat-out speculating regarding any real-world scenarios in the mathematical models. Can you actually address the point I was making instead of focusing on a minuscule part of a post?


Quote:
Sure, given the assumed safe spacing. To put it the other way around, people have calculated that safe spacing distance based on the assumption you will be travelling around that fast.
And yet again, I never once said anything about spacing. You are yet again putting words in my mouth. This is why having a simple conversation with you is difficult.

Quote:
That's just wrong. Again, read the link above--that is all about the loss of friction when the tires are still rolling.
And yet again, in my scenario (that you are blatantly ignoring) this effect is negligible.

Quote:
Once again, though, you are inadvertently raising a good issue. If your tires do lock, you are suddenly in MUCH worse shape in wet conditions. In dry conditions, locked tires are only slightly less effective at braking as unlocked tires. Wet tires, on the other hand, will experience a further dramatic decrease in friction. Here is someone who goes into that issue (estimating locked tires on a wet road could drop as low as 0.1 from the already lower 0.4 for rolling tires on wet roads):

Friction and Automobile Tires
Obviously...this isn't 'inadvertently raising a good issue'. This is a non-issue. Everyone knows if wheels lock you are in a much worse position....


Quote:
I actually don't want to ARGUE physics with you, and here is why. I am citing actual physics professors discussing these issues. I'm afraid that if we instead try to argue about this in a usual Internet forum way, people might get the impression there is some doubt about the subject.

In fact, there is not, and this is one of the few cases where I am going to suggest people accept an argument from authority: please listen to the physicists, and not a random Internet poster. Because this issue is too important on a direct, personal level for people to be left in doubt about what is right.
And yet again, you are taking a general form to argue the specific case that I cited. You are focusing so much on the numbers and data that you flat-out missed my point.

Last edited by hnsq; 11-15-2011 at 11:46 AM..
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Old 11-15-2011, 11:50 AM
 
Location: Wilkinsburg
1,661 posts, read 1,311,663 times
Reputation: 962
Quote:
Originally Posted by hnsq View Post
The issue is point at which you lose breaking force when your tires lock and slide.
I'm not trying to be a jerk, but I really don't know what you're trying to say.

Quote:
Originally Posted by hnsq View Post
In the case of an emergency, where does the act of breaking suffer? The answer to this question is such that as a person increases force on a brake pedal,
Again, whatever it is you're trying to say is not clear. It is noteworthy though that ABS braking systems have pumps which make the relationship between pedal force and caliper force a little tricky.

Quote:
Originally Posted by hnsq View Post
here is a point at which static friction exceeds kinetic, thus causing a car to lose control. That point is lower assuming a tire is locked, and there is no standing water.
Static friction has nothing to do with what we're talking about. The car is moving, the tire is moving relative to the road surface, and when the car is braking the tire is either sliding or almost sliding relative to the road surface.

A coefficient of static friction would perhaps be useful in calculating whether a car would slide in the radial direction around a curve (and lose control), but that's not what we're debating. That is because technically, when a body is traveling around a curve, the radial velocity is zero (the entire velocity is in the tangential direction). That gets complicated though, and a very good solution to that problem would be a little beyond the scope simple classical physics.

Quote:
Originally Posted by hnsq View Post
Now do you really want to discuss physics, or can we talk about how stupid it is to drive 55 on the parkway when there is a light drizzle, like Pittsburgh drivers do every time it rains?
It doesn't make sense to separate those issues. The change in driver behavior is necessitated by the change in the physics of driving over a wet and dry surface, and the logical desire to not incur an increased risk of having an accident. The fact that you think that's stupid, despite the laws of nature which suggest otherwise, is simply illogical.

Last edited by ML North; 11-15-2011 at 11:59 AM..
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Old 11-15-2011, 12:11 PM
 
Location: Wilkinsburg
1,661 posts, read 1,311,663 times
Reputation: 962
Quote:
Originally Posted by hnsq View Post
But you are (yet again) completely missing the point. You are (yet again) focusing so much on one tiny detail that you miss the point altogether. Obviously there is less friction on wet roads. How many times do I have to say that? In my scenario (70mph in a light drizzle), you are in no more danger of losing control than you are on a dry road. Can you actually address the point I was making instead of focusing on a minuscule part of a post?
This is wrong. Perhaps on a straight road, and ignoring the effect of decreased visibility, and assuming there are no other cars on the road, you could make this argument, but those are clearly not reasonable assumptions.

Quote:
Originally Posted by ML North View Post
A coefficient of static friction would perhaps be useful in calculating whether a car would slide in the radial direction around a curve (and lose control), but that's not what we're debating.
Ok, now we'll debate the issue of losing control, whereas before we were clearly talking about stopping distance.

Whether you're negotiating a bend in the road or changing lanes, there are lateral forces acting on your tires that are perpendicular to the direction of travel. The reactive force that keeps your car from sliding in the radial direction is equal to a coefficient of static friction (because ideally your radial velocity is zero) times the normal force (which is equal and opposite to the weight of the car on a flat surface). Because that coefficient of friction decreases due to a wet road surface, the speed at which your vehicle will slide in the radial direction (and lose control) is decreased. If you maintain the same speed, you are closer to the point of losing control and have less of a safety margin, and therefore definitely have a higher risk of being in an accident.
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