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Old 11-02-2009, 02:29 AM   #51 (permalink)
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Quote:
Originally Posted by doviatt View Post
I completely agree with you first paragraph and would add- remember it is a maximum speed limit legally but safety judgment is in your own hands.

But your second I cant quite agree with. Water is an incompressible medium all of the molecules have to, by natures law, go the same speed. Traffic is more like air. Air wants naturally to be a certain distance from the next molecule. Pressure will reduce this distance. Traffic behaves the same way as air. When stopped at a jam- Bumper to bumper- high pressure. The distance between does increase with speed. On and off ramps, and curves cause turbulence and pressure differentials.
If you increase the number of molecules without increasing the speed through the hose you will get a pressure increase, if you put a restriction in the hose it will slow the flow and the pressure will increase and as you alluded to with cars this will cause them to do things like slow down, bounce off each other, and otherwise disrupt the cars coming from upstream. By reducing the restrictions to the flow of molecules you get a reduction in pressure the result is higher velocity through the hose.

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Old 11-02-2009, 04:25 AM   #52 (permalink)
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Cars don't act like air or water. They act like cars. With drivers. All the cars are different. All the drives are different. Unless there is an accident, none of the cars touches each other, unlike water or air molecules. Molecules don't do stupid things like change lanes at random or get drunk and drive upstream with the headlights off, either. (Or do they?!?!)

What you're dealing with is the perception of the drivers. Some drivers sense that others are "way too close" or going "way too fast". Other drivers might be in a car with a larger performance envelope and have better driving skills. (Think: 'The Stig' in a new Porsche on sticky tires.)
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Old 11-02-2009, 05:19 AM   #53 (permalink)
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I think that the capacity of a road stays the same regardless of the speed limit. Yes, it take a car less time to do a certain stretch of road, but the distances between cars are greater. By how much? Let's assume everyone drives using the 3 second (or 2 second, or whatever) rule regardless of speed. That means that for each lane one vehicle passes a certain point every 3 seconds. This doesn't depend on the speed of the vehicles (above a certain speed, of course).

Aspera: Your example of the two drivers, one driving for 5 hours and the other 8h, reminds me of a local politician who wanted to win the votes of both drivers and ecologists by proposing to get rid of all speed limits. He argued that the faster you drive the less fuel you need, because you have less time to use fuel, etc.
Of course, driver fatigue is very important, but I don't believe that driving at 80mph for 5h is safer than @50mph for 8h.

In most European countries (with some local exeptions) the speed limits are:
  • 50 km/h urban,
  • 90 km/h rural,
  • 110 km/h expressways,
  • 130 km/h highways.
During last year's oil price hike some countries lowered the last two to 100km/h and 120km/h, resp. Since then more countries are thinking about doing this (I believe that CO2 emissions has something to do with it). Unfortunately, at the same time Poland's ministry of transportation proposed raising those speed limits to 120km/h and 140km/h. Why? Nobody knows...
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[Old] Piwoslaw's Peugeot 307sw modding thread
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Old 11-02-2009, 09:30 AM   #54 (permalink)
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Originally Posted by Piwoslaw View Post
Aspera: Your example of the two drivers, one driving for 5 hours and the other 8h, reminds me of a local politician who wanted to win the votes of both drivers and ecologists by proposing to get rid of all speed limits. He argued that the faster you drive the less fuel you need, because you have less time to use fuel, etc.
Of course, driver fatigue is very important, but I don't believe that driving at 80mph for 5h is safer than @50mph for 8h.
So you admit that the slow driver will suffer three additional hours of driver fatigue...but still contend that driving at 50mph is safer than driving at 80mph? Operator fatigue can be nearly as dangerous as driving drunk. Naturally, I don't suggest a 16 year old with a fresh driver's license drive 80mph down a hilly gravel road at night in a full sized van. I'm talking about an Interstate like I-70 from Kansas City to (almost) Denver under good conditions with good equipment in good order with a good driver. If there is ZERO other traffic, then both drivers have just about equal risk. If there is NORMAL traffic, the speedy driver is much safer than the slowpoke with the 20mph+ traffic speed difference.

Apples to apples, the faster driver would use more fuel, spend more money, and cause more pollution. But that's why we shouldn't be driving apples.
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Old 11-02-2009, 09:30 AM   #55 (permalink)
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People bring up safety when they are losing the argument
...or counting "tombstones" along side the highways.
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Old 11-02-2009, 09:32 AM   #56 (permalink)
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as a result of driving too fast?
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Old 11-02-2009, 09:33 AM   #57 (permalink)
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as a result of driving too fast?
How fast is too fast?
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Old 11-02-2009, 09:34 AM   #58 (permalink)
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As the article points out, the average driver actually slowed down when the speed limit was raised in Utah. It just points to the fact that speed limits on the highway are essentially irrelevant. They are only there as a revenue source for local PD.
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Old 11-02-2009, 09:41 AM   #59 (permalink)
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tjts1, I agree.

Have you been to radardetector.net? They've got some good data over there. Another forum that I think you guys would love is landracing.com. If 'speed kills' all of the people on these two forums would already be dead. (So would anyone that's been in an airplane...500mph!!!)
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Old 11-02-2009, 09:47 AM   #60 (permalink)
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Quote:
Originally Posted by aspera View Post
How fast is too fast?
for an ecomodder forum? that depends on how many aeromods and other regearing/retuning mods you have done

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