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# Know Physics; No Congestion

High Speed vs. Traffic Bottlenecks
 (+3, -6) [vote for, against]

:) Before I get to the main topic, I might as well confess that the title is a pun (old medical terminology).

Anyway, most anyone who has played with a garden hose knows that after the flow of water is turned one, the placing of a finger or thumb over the end of the hose makes the water flow out faster. This is simple Physics, in which the volume of material that passes through a given opening depends on the size of the opening and on the speed of the material. Using a finger to reduce the opening at the end of a hose causes pressure to build up, and increased pressure is a Force that causes Mass to Accelerate. If one liter per minute of water flows slowly before applying a finger, just about one liter per minute is STILL going to flow, faster, after applying a finger.

Now, with respect to cars and traffic jams, they are quite equivalent to water in a hose, with pressure building up in the drivers...who are NOT allowed, by law, to go faster!

Well, laws can be changed! Take a cue from Physics! If you want to squeeze four lanes of traffic down to two, then the speed limit on that two-lane section of road NEEDS to be twice that of the speed limit on the four-lane road! If an accident occurs, and people want to rubberneck, gawk, and otherwise slow down traffic, just place some portable tempory High Speed Limit signs around the vicinity, with big enough numbers that even the nosiest gossipper would rather go fast, legally (if only for a short distance). If your local landscape includes a tunnel that causes drivers with claustrophobia to slow to a crawl, just raise the speed limit so high, in the tunnel, that the desire to go fast will overwhelm the claustrophobia (not to mention making the time spent in the tunnel, BY claustrophobes, much shorter!).

Yes, I know that high speeds carry their own dangers. For example, the ones who try to both gawk AND go fast will probably remove themselves from the gene pool. So? When has Physics ever favored fools?

 — Vernon, May 08 2003

The real reason people stop on freeways. http://www.straight...assics/a1_028b.html
[disbomber, Apr 09 2005]

Many nice simulators [csea, Apr 11 2005]

MGP Speed Limit MPG_20Speed_20Limit
Older Idea mentioned in an annotation here. [Vernon, Apr 12 2005]

Don't forget to add a minimum speed limit in such places.
 — Worldgineer, May 08 2003

Perhaps those places should all be marked "Begin NO SPEED LIMIT ZONE" and, at the end of the zone, "RETURN TO SPEED LIMIT of ..."
 — Vernon, May 08 2003

 As you pointed out, there is still the same amount of volume (one liter / minute in your example) no matter the velocity. If a portion of the volume is flowing faster, a larger portion must be flowing slower.

 If successful, your concept will create a larger amount of slower traffic to compensate for the small amount of faster moving traffic, resulting in a fishbone for you.

Just buy a motorcycle and let traffic happen to other people.
 — ato_de, May 08 2003

 [ato] //larger amounts of slower traffic// Well that's unavoidable due to the bottleneck. This isn't compensating for the faster traffic, but is being caused by the bottleneck. The faster traffic is an attempt to compensate for the slower traffic, keeping the total time for your journey as close as possible to what it would be if there was no bottleneck.

[dag] Bernoulli's isn't completely applicable. Though you're right about compressibility, Bernoulli hadn't thought to consider self-accelerating particles.
 — Worldgineer, May 08 2003

 ato_de, Wordgineer has the right of it; you are mistaken. Remember that when the faucet is on, a garden hose is completely FULL of water; this is not true of roads -- unless a jam is happening. See below.

 dag, traffic IS compressible, because of the spacing between cars. That spacing is what mostly disappears when a jam happens, and allowing high speed is a way to put space back, between the cars. That is, IF we could post SPEED LIMIT RESCINDED signs at a bottleneck (say a wreck in one traffic lane) as soon as the bottleneck occurs (something a rewritten law would have the first cop on the scene do), then the speed-up of cars in the "open" lanes makes room for the cars in the "closed" lane to move over. The net result is that the cars get to go by the wreck with little overall effect on the flow of traffic.

Currently, of course, cars just accumulate behind the wreck, and the compression of traffic remains for quite some time even after the wreck is cleared.
 — Vernon, May 08 2003

 Thanks [Worldgineer] I missed that it was a compensation/reaction. I still don't think it would work. People do not behave like liquids unless you subject them to extreme temperatures, and even then, there are problems.

[Vernon] if I ever meet another person who knows how to merge, I might go to a neutral position on this concept.
 — ato_de, May 08 2003

I love it. I've always suspected there are properties of traffic flow waiting to be discovered. Probably a combination of compressible fluid dynamics and sociology.
 — Worldgineer, May 08 2003

//People do not behave like liquids unless you subject them to extreme temperatures//. oh toady, you do make me laugh.
 — po, May 08 2003

 ato_de, yes, I can see how this idea might lead to more accidents. But only for the short term. In the long term, those who can't cope will be weeded out of the traffic system. Still, I think most people can learn it. ESPECIALLY that's what Traffic School should have them practice!

dag, when there is no traffic you should probably obey the speed limit signs. They do generally exist for one or more valid reasons.
 — Vernon, May 08 2003

While we're discussing physics and bernoulli, let's throw this into the mix: If we're going to treat traffic as a compressible fluid, we need to talk about pressure effects. If we treat the spacing of the cars as analagous to pressure (more spacing=less pressure), then we need to take into account that as speed increases, pressure tends to decrease. This is often seen in traffic, as sensible drivers tend to increase their spacing as they increase speed. In terms of squeezing traffic from two lanes down to one lane, you'd need to double your speed just to maintain equal pressure. Since pressure must decrease as speed increases, you need to quadruple your speed in order to successfully transport the same traffic. To extend to other numbers of lanes and constrictions, the required speed changes as a function of the inverse square of the constriction percentage. I for one have no intention of trying to push my car to 240 mph in heavy traffic just to get somewhere a few minutes earlier. fishbone.
 — Freefall, May 08 2003

//in heavy traffic // Not if you're giving yourself the described spacing.
 — Worldgineer, May 08 2003

What is needed are snipers.
 — thumbwax, May 08 2003

Ok ok, I can see that it's in all probability not feasible, but I'm having fun just imagining...
 — kmlabs, May 09 2003

What I love is the combination of Fluid Dynamics and Biology - ie: Bernoulli and Darwin: fluid dynamics for vehicles, with Darwinian evolution for the poorer drivers. I say: increase the speed limit on the whole road (equivalent to altering the coefficient of surface friction in the garden hose), to compensate for the random slowing at one point. This will also have the added benefit of reducing the time required for the Darwinian phase of the system to operate.
 — Crashinoz, Dec 29 2003

 What causes congestion isn't slow speeds, it's drivers' fear of getting in an accident. The more people are on the road, the more they all become afraid of hitting each other, and the more they slow down, until eventually everyone stops and does a gradual crawl every few minutes. (This is otherwise known as The Southern California Experience.) Raising speeds wouldn't do jack shit, except have people *start out* faster--meaning more people get in accidents and then people get more afraid, which makes the problem worse.

A+ for effort, but no croissant.
 — disbomber, Apr 09 2005

 // those who can't cope will be weeded out //

Hmmm. When does the hunting season start on the freeway, again?
 — moomintroll, Apr 09 2005

[moomintroll], no hunting needed; they weed themselves out.
 — Vernon, Apr 10 2005

...quietly in their own homes, or in a long series of spectacular pileups over the course of many years?
 — moomintroll, Apr 10 2005

More the latter. Consider an ordinary accident, blocking one lane. The cops post faster-speed-limit signs to keep the overall traffic flow going. Some rubbernecker fails to pay close enough attention and crashes, blocking another lane. Now the cops raise the speed limit even more. More idiots crash. The whole road would be blocked except by now the wrecking trucks have managed to clear one of the original lanes. There is an element of comedy here, but the net effect is that by the end of the day, a reasonable number of fools have departed, leaving the roads safer for the rest of us.
 — Vernon, Apr 11 2005

 I think that the best way to make the roads safe would be to ensure you never get anywhere near implementing this idea. If it was safe for the majority of people to drive at 150mph when all lanes were open, the speed limit wouldn't be 70mph (UK).

 /dag, when there is no traffic you should probably obey the speed limit signs. They do generally exist for one or more valid reasons./

You fail to mention what they are, or why they are no longer valid reasons if somebody crashes.
 — david_scothern, Apr 11 2005

This is a great idea. I spent some of Sunday evening in the usual tailback on the A3 as three lanes of traffic limited to 50mph merge into a single lane limited to 40mph. Instead we could all accelerate to 150mph before shuffling for a space in the one remaining lane and negotiating the Wandsworth one-way system. I'll need a faster car though.
 — wagster, Apr 11 2005

[Vernon] I'm just wondering. Do you actually think this would be a good idea or are you just trying to find a practical application for this kind of physics?
 — hidden truths, Apr 11 2005

 [david_scothern], the main good reason for speed limits is that it saves gas. Air resistance is such that to double the speed, rather more than double the power (eight times, I read somewhere) is needed. On the other hand, idling your way through a traffic jam because of an accident doesn't save fuel either. So, TEMPORARILY AND LOCALLY increasing the speed limit allows the drivers to be less frustrated, which is a different valuable savings, altogether.

Please note that I see the Darwinian weeding as a beneficial side-effect to this idea, and not the main reason for it.
 — Vernon, Apr 11 2005

 Similarly, the reason for 30mph speed limits in residential zones is to keep up the purity of the air? Speed limits are about safety as well as fuel use.

Air resistance rises with the square of the speed, by the way.
 — david_scothern, Apr 11 2005

residential speed limits are there to protect pedestrians and children.
 — Vernon, Apr 11 2005

Perhaps if the cars were molten?
 — bristolz, Apr 11 2005

I've posted a [link] to a page of interesting articles and simulators. Kind of interesting to "play God" with traffic.
 — csea, Apr 11 2005

 — daseva, Apr 11 2005

 [Vernon], if national speed limits were solely about fuel savings: - more efficient cars would be allowed to go faster or - less efficient cars would be legislated against.

 I think that there may also be a safety issue here, which would be exacerbated by accelerating the traffic to speeds drivers were unaccustomed to, and doing this solely in danger zones.

Also, your "darwinian weeding" of all the fools, leaving only us demonstrably safe, sane people, would inevitably lead to heavy casualties among us normal, superior drivers who just happened to be in the way when the good-for-nothing 150mph rubbernecker crashed into us.
 — david_scothern, Apr 12 2005

 Regarding efficint cars and speed limits, see my "MPG Speed Limit" idea in the "Cars: Speed Limit" area (linked). As for legislating against low-mileage vehicles, they HAVE done that after a fashion, by mandating an average fuel-economy level across all models sold. Yes, it could be done better, but what they've actually done is better than nothing.

 Yes, of course there are safety issues. The cops, ambulance crew, and wreckers getting out of their vehicles to do their jobs at an accident scene will all be endangered by faster traffic. I actually regard this as more important than the safety of otherwise-safe drivers who might get hit by the reckless (speed difference during such collision is lots less, and the safe driver is SUPPOSED to be "driving defensively" and looking out for the idiots).

With respect to all drivers learning to work with this speed-up-and-merge system, the place to start is on roads where the normal speed limit is 40mph (65kph) or less. Then the sped-up traffic will still be moving at speeds not far from what is normal in other places. Note they could deliberately shut down a lane here and there, with nobody endangered in the shut-down zone, just to provide places that speed-up-and-merge can be practiced.
 — Vernon, Apr 12 2005

 You're quite right. I'm supposed to be keeping a safe distance from the car in front and the one behind, while driving at high speed and allowing traffic to merge smoothly (not unreasonable). Should somebody sideswipe me or push me into the reservation, that's my fault for not avoiding.

 And then, when my car flips, rolls and lands upside down on its roof in the path of the following traffic, it is up to them to avoid me, even though there are no available lanes for them to do so in. Should a few of them die, well, they were obviously not safe enough drivers in the first place.

 And saying that people deserve to die if they're stupid enough to rubberneck at an accident site? Driving fast without watching the road is stupid, perhaps criminally so, but the death penalty? That's simply immoral.

 I honestly don't understand how you can advocate driving at high speed through danger zones. Still less can I understand you admitting that this will lead to more deaths, yet still proposing it as a sensible suggestion. More accidents = less lanes free = higher speed = more accidents. Road closed. Why is this a good idea?

Further to that lot, there is the simple point that accidents will quite often result in total road closures until one or more lanes can be reopened. The neat, mathematical analysis that says "a fool crashes and a lane is closed, then another one does and another lane closes" is incorrect. What happens when a semi hits something and jack-knifes? Or when debris is flung across the carrigeway from an accident? Anything that raises the chance of accidents will reduce the throughput of the road.
 — david_scothern, Apr 12 2005

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