Traffic Jams

From your post I take it you have little driving experience in real traffic or more than likely do not even have a drivers licence?

Try driving 40 feet or less apart in traffic going over 20 MPH and then try and get on the brakes before you rear end the idiot in front of you that got on his. Thats what the proportional two second following rule is for.

A good enough point, but how much "real traffic" is there around Minot? In LA, Boston, or Seattle, to name a few, the OP's strategy is completely freakin' impossible.

I have been through the bigger cities many times. The worst is driving my pickup while pulling a loaded trailer though that crap. Every time I end up with some moron who thinks he needs to follow two car lengths off my pickup bumper despite there being 25 feet of flatbed trailer already in that space.

Yea around Minot the closest thing we get to a traffic jam is when a few wild turkeys get on the road and decide to stand their ground against some city girl in a small car and more than three of us end up stuck behind her.

The 2 second rule is impossible in LA or anywhere but nearly deserted freeways

If you try to leave 2 seconds you might as well park it, as you will quickly feel as if you are going backwards. When speeds drop below 40mph you are lucky if you can leave 2 car lengths....

I mis-typed... Two-seconds at speed and two car lengths when moving slowly. Allowing vehicles to easily merge without braking.

Will not work and here is why:

So, you leave two seconds between you and the car in front of you... so another car can merge...

When another car merges in the space you had in front of you, both you and the merged car in front of you are now in violation of the 2-second rule....

So, what do you do??? Both hit the brakes so that both of you are in compliance.

Have you heard of the accordion syndrome?

It is easy to observe when traffic is heavy. Vehicle A, for some reason, hits his brakes lightly, perhaps due to a motorist or accident on the side of the road, to slow down just a little. Or, it could be the example I just gave where a motorist merges.

Vehicle B behind A must also slow, but due to physics he must slow down a little more than A did. Vehicle C follows suit, as does D, E, F, G, and so on. Each car is forced to slow more than the car in front.

Soon, cars are coming to a near stop. Now we have a traffic jam.

I think one of the earlier posters was right - you just haven't had enough real world driving experience to understand what is wrong with your proposal. That's okay. Everyone was a beginner at one point. Just keep analyzing the problems you see and think of solutions. Most may be wrong (still good practice), but who knows what you might solve that no one else has. :-)

It seems the accordion effect is more extreme when the cars are packed more closely together than if there is plenty of room to absorb speed changes. If a car merges in front when there is plenty of room, then micro speed adjustment to compensate for space is simple. If a car merges when there is little space then one is forced to brake, causing the accordion effect. Every traffic jam I have been is is caused by a bottle-neck of lanes, three lanes into two, etc... if the lanes allowed the merge lane free flow into the other lane there should be no (or minimal) braking and an easy flow of traffic. In some places there is an effort to do this with one car traffic lights for cars coming onto the highways.

I think you mean 2 second rule

I just saw your correction. And I believe that may have been updated to a 3 second rule. But if you have ever driven on california highways. They have a very short 3 secondsmore closer to the 2 car lengths rule.

Yair, and my idea is all cars link up with tow bars to trucks and act like trains with cool engage and disengage couplings enhancing drafting safety like when you get closer and closer because it is cold.

My other idea is a flat world, or the electric road, and I like the pocket airport, and I used to ride a bicycle.

Cars don't drive, people do.

The fold up paper parking space is handy too, you can keep it in you pocket and just take it out and unfold it when you get to your detsination, great in congested cities
Del

The fastest flow of traffic on a motorway is when all are driving at the same speed.

My driving policy is to be at a reasonable safe distance from the traffic ahead and set my cruise control to the general speed at the time. Never in a hurry, never use the fast lane, and avoid lane changes to the minimum.

Sometimes one could travel for miles at this speed.

As soon as there is a change the traffic congestion one then have to change the selected speed.

The problem in traffic is the ones that want to make up time on motorway and move into the space in front causing me (and the train behind me) to fall back - sometimes almost back up to the starting point. -

Dosing all the hurried with Prozac (or similar) may help.

Cruise control in traffic is a bad idea. Traffic speeds tend to vary, so you are always adjusting yours to compensate and cruise control tends to cost you some time in the event you must suddenly stop:

1. your foot is not optimally placed to get on the brakes. You build muscle memory when you drive with foot on accelerator and transition to brake pedal.

2. You loose deceleration time. Normally, when you transition from accelerator to brake your car gains advantage from the deceleration when your foot comes off the brake.

The last bad thing about cruise control is that it is a killer in the rain. My girlfriend worked as a medic and it is not uncommon to have a car loose control due to cruise control in the rain.

When a car hydroplanes with the cruise control on, the car's cruse control gets spoofed by incorrect vehicle speeds when it hydroplanes. This can cause the engine to speed up or down trying to maintain set speed and compound the problem and contribute to a crash.

This is a little known issue with cruise control, but real.

You're absolutely right about cruise control in the rain. (Don't do it!)

I think maybe what hendrik was talking about, is what I do. If traveling on the highway, I'll adjust my speed until I can safely have a clear pocket all to myself, several hundred yards between me and the car in front of me. On a good day, I can maintain this clear zone for 100 miles or more. Other than that scenario, I don't use cruise control.

Yair, I don't use cruise control either. I also do work at maintaining one car length per 10 miles per hour, and change lanes to maintain that.

I am aware that many drivers do not account at all for weather, and when on fast moving interstates have been known to get off and take another route when rain starts to come down predicting crashes reported on the radio as we continued to our destination by the alternate route.

One pet peeve of mine is that many drivers do not even understand that trucks want to go faster downhill so they can get up the next and stubbornly block the truck and wonder why its on their ass.

"t peeve of mine is that many drivers do not even understand that trucks want to go faster downhill so they can get up the next and stubbornly block the truck and wonder why its on their ass."

Never happens in Florida! Then again, we don't have hills. ;-)

Yeah, there aren't hardly hills or mountains in Florida, but it does have some unique hazards such as older drivers who ought to have given it up and do some odd things.

Even locally I am aware of an older lady who is on heavy drugs like morphine, and drives at 45 miles an hour regardless of whether she is on a country gravel road or the highway.

So as said, "Cars don't drive, people do."

As an aside, it was interesting to hear from a friend of mine about traffic in the Rochester New York metropolitan area. He said that the highway system around there had been built for an anticipated 5 million whereas due to economic forces et al, the population was much lower at something like 1.5 million so getting around was right easy.

Florida is unique on another score as I am pretty sure there have been headons between airplanes there.

I went on a round trip yesterday and at some stage discovered that I am not using speed control , but did so when the traffic was less dense and on a rural road with a speed limit. And did turn it off when light rain started

When using speed control I am forced to be more aware of the traffic and is constantly calculating and adjusting.

The 3 litre Camry deactivate cruise control on the touch of the brake pedal.

Do you drive?

Make sure to text or twitter that idea to everyone on their Blackberries and Ipods otherwise they may not get the memo. Don't worry, they can read and drive at the same time.

Definitely,this photo for Cairo downtown.

Sameh-Cairo

Yes, it is. I've never been there, just pulled up a random traffic jam picture.

Have you ever driven on a highway in New Jersey or, God forbid, New York? If you leave enough space for a piece of paper between you and the car in front of you someone will cut in. If you attempted to use your rule here in NJ you would NEVER get out of your driveway. In case you haven't noticed... courtesy is dead on most of the roadways in the larger cities of the world.( I won't even start on India )

No insult intended but this is the truth. Your idea wouldn't even work in an ideal world. Imagine if people were kind enough to follow that directive, go up a couple of posts and read about the accordion effect.

In NJ and NY we have a law stating that if a pedestrian steps off of the curb drivers MUST stop and allow them to cross the street. I dare you to give that a try in NYC or almost anywhere in NJ.

From sing365.com, and James Taylor:

Damn this traffic jam
How I hate to be late
It hurts my motor to go so slow
Damn this traffic jam
Time I get home my supper'll be cold
Damn this traffic jam

Well I left my job about 5 o'clock
It took fifteen minutes go three blocks
Just in time to stand in line
With a freeway looking like a parking lot

- Chorus -

Now I almost had a heart attack
Looking in my rear view mirror
I saw myself the next car back
Looking in the rear view mirror
'Bout to have a heart attack
I said

- Chorus -

Now when I die I don't want no coffin
I thought about it all too often
Just strap me in behind the wheel
And bury me with my automobile

- Chorus -

Damn...

Now I used to think that I was cool
Running around on fossil fuel
Until I saw what I was doing

How's this: Butt chip transmits to bumper sign age of driver?

this is driving 101..

you shouldn't have any more questions

What's needed is little buggies, all controlled via central computer.

Absolute nonsense. (op)
Two car lengths, say 40ft tops, gives less than 1 sec. to stop at 30mph. (44ft/sec.)
(and I have had my share of morons into the back of me doing this - including being
in a light truck doing 60mph in torrential rain, less than 20ft from the one in front!)

Which is why we have (daily) motor pile ups. These people "play the odds" and
probably cannot do straight arithmetic! If "relatively" safe drivers leave a 2 second
gap, which should be more than 100ft plus, (at 30mph - think tennis court length)
what happens? A new moron enters the "vacant" space, Halving all safety margins.

Joining them together would not be that difficult. (then drive them over a cliff)
No seriously; I previously thought an electro-magnetic coupling front and rear,
would allow vehicles to couple-up while in motion, and de-couple at the flick of
the switch, when choosing to go a different way.

Any vehicle using this (my system) could magnetically connect (itself) to any
other in front, and then release itself as their junction or turn-off approached.
In fact the only downside I can see to this is one may be "towing" the twenty
cars behind! Achieving a personal best of about 5 mpg!

This could be a very valid alternative, if a limit to the connections (train) was
legally established. e.g. 5 cars linked max. - and it would all be self motivated!
Such that everyone would be looking to join-up with any vehicle in front.
I estimate a 50% national saving in fuel overnight. eerr... yes, you can go first.

jt.

Merry Christmas to you all - and let's have a Happy New Year!

why is it when listening people talk about traffic it's interesting that the story is always everyone else is a moron when they are driving.

your not sarcastic. I was told do not pass a car around a curve with a yellow line. I have seen this often.

My recent research has found a glaring translation error in the Bible.

It's not that The meek shall inherit the Earth. It is The Stupid shall inherit the Earth.

I wish I could say I am free of guilt but I can't .....on the bright side....i have a large inheridence coming.... ; )

Agreed. California written test is 20 questions, T/F, requiring a 80%. Germany is 400 questions, multiple choice, requiring 90%. Plus a one-month intensive driving course.

You missed my correction. I meant 2 car lengths minimum (very slow speeds) and 2 seconds (more is better) at higher speeds. I think the slow speed room is key, giving a place for lanes to merge rather than bottle-necking, which seems to be the main cause of traffic jams on highways. It would require a certain awareness and courtesy, so probably a pipe dream...

I see the point phoenix but think anyone who (IMO) needlessly risk the lives
of potentially many people, and thoughtlessly encourages the likely suffering by
mutilation, with the inevitable follow-on of months in hospital and life time pain,
to "save" a few minutes by driving to close, is entitled to be called moronic.

You need only to converse with a few ambulance drivers and traffic police
to have this opinion emphatically confirmed. My son, one of many, has suffered
seriously by careless driving, and I believe anyone who has been personally
affected will have no hesitation in substantiating it. Simply... Why?

jt.

I wish no one offence, only to call a spade a spade.

I have been saying this to friends, family and associates for over 10 years - if others would adopt our way of thinking we'd have something!!!!

There is no magic formula that works for all cars. Trucks are heavier and take longer to stop than a Smart car (saw a nasty picture of one crushed between two trucks). I drive a limousine now and then...loaded with 10 people I'd never follow less than 6 or 7 car lengths at speed. The "general rule" that I grew up with was 1 car length for every 10MPH you are traveling. I find that easier to teach to people than rules based on seconds...everyone has a different idea of how long a second is...you can SEE how long a car is.

While in places where the density of traffic is low enough these kinds of guidelines are fine & in no way new concepts, you will find it in all drivers training materials.

Maintain a speed allowing the other traffic to continually pass you limits the degree of traffic jam one may experience.

Most jams occur due bad driving habits.

All the ones I have been in are due to volume.

It may seem so on the face of it but most occur as the mild to very aggressive drivers attempt to be first cutout the possibility of or delay another gaining access to a lane or roadway. This occurs routinely but when more volume is introduced the spectrum broadens rapidly until a jam is the result.

In 99% of cases our roadways can handle the volume but driving habits don't include enough tolerance to allow flow. Visualize two pitchers of water, one with ice cubes one without. Attempting to pour the iced one causes the cubes to congest at the spout and limiting the free flow of water without spilling.

Typically during high traffic volumes traffic bunches up, where as if proper following distances where maintained the flow doesn't become reduced to the point of stagnation and flow can be allowed.

Please clarify your point. Is your contention that the root causes of traffic jams are due to aggressive driver behavior?

If so, I would say that the root cause of traffic jams is the volume of traffic demand is greater than the available capacity of the road.

I agree that operators do not drive in the most efficient manner, but even casual observation will tell you that volume is the major player.

Case in point, on a multilane highway with a traffic density of X will produce a flow of Y. When you introduce more traffic (such as an on ramp) the flow rate decreases.

Imagine a steady state condition where each vehicle is following at a safe distance and the cars are moving at near the same relative speeds (critical density). Cars are free flowing. When you introduce additional vehicles either the current traffic must compress their following distances to accommodate the new vehicles or approaching vehicles must slow down to maintain distances, which ripples backward in a congestion shockwave (or more likely both happen).

This is the accordion effect and the net result is traffic congestion (jam density). While maintaining a proper following distance may help, once the highway reaches a critical mass (> critical density) any new traffic will cause a decrease in traffic flow rate and you enter the jam density.

Another observation that tells us that the above is correct is the introduction of traffic lights at the end of on-ramps. The idea is to limit or meter the number of vehicles onto the highway to minimize the negative effect of too much traffic at one time. In other words, keep the traffic density just below the critical density.

Another big player as to why we have traffic jams has to do with money. If you study traffic loading patterns you will see in many cases the congestion is limited to relatively short periods. Building a road that easily manages the worst case scenario is the dream, but that dream costs money and in most cases a luxury that few cities can afford, so congestion is planned for and managed to a level that is felt to be tolerable. However, you can still expect a statistical number of days of traffic jams no matter what.

Traffic flow is a highly technical science and is a not linear one at that. There are many reasons for the effects we see and those effects interact to create even more complex effects.

Driving habits have a role in what happens, but the reality is that engineers must account for human nature. It is far more feasible to add additional lanes to a road than to change human nature. It's not going to happen. Transportation engineers have known that for better than 50 years and that is the reason things are the way they are. We can sit on a barstool and opine about how much better life would be if only everyone did this or that, but at 8:00AM you still have to get up and deal with reality, be it driving to work or working to make other's drives better.

I've greater than casual observation and I believe you are taking much for granted and overlooking the obvious. The obvious being if proper driving attitudes and following distances are maintained volume will reach a peak but not exceed the level which the thoroughfare is designed to carry. Our roadways are designed for those following the rules and when rules are broken the design model suffers but is not at fault. What folly to think proper following distances when observed may allow vehicular control to the point of a controlled stop w/o contacting the vehicle in front at all.

Help me with this statement you wrote, "The obvious being if proper driving attitudes and following distances are maintained volume will reach a peak but not exceed the level which the thoroughfare is designed to carry."

If that means, it is obvious that simply maintaining correct vehicle following distances will prevent a traffic jam, then it would be a fallacy.

It is certainly possible to continue to add more and more vehicles to a road so as to exceed the critical density for that roadway. No amount of driving behavior can prevent that from happening.

You also wrote, "Our roadways are designed for those following the rules and when rules are broken the design model suffers but is not at fault."

My understanding is that human behavior is one of the factors that is used in the design of roads. It would be silly to do otherwise.

I am sure you can sit down and mathematically derive an optimum driving behavior and use that as a driving model to design a road, but it would result in an inefficient road.

Human behavior is a critical factor in the design of any system and highly critical where failure of these systems could result in a catastrophic loss. I have expertise in aircraft human factors and I can tell you that the attention to detail is mind numbing and for good reasons.

I guess you could argue that the degree of abuse of the rules is what you meant, but everything is designed with a certain safety factor to it and roadways are no different. However, roadways are designed with some degree of understanding that the rules will be broken. Even those yellow suggested speed signs on curves and ramps have a built in safety margin of about 2X.

Help me with this statement you wrote, "The obvious being if proper driving attitudes and following distances are maintained volume will reach a peak but not exceed the level which the thoroughfare is designed to carry." Help: If the proper distances were maintained there wouldn't be room to add more vehicles after reaching the design peak. Try it, try putting more than three lbs coffee in that three lb bag. You're saying drivers will crowd on anyway causing a jam, hence my description of poor driving habits.

It's simply unreasonable to expect that:

1. Drivers can and will maintain perfect synchronous motion and therefore always maintain perfect position. In the real world, people change lanes, exit roadways, slow down for curves, etc. This is driving, not the Blue Angles formation flying.

2. People will approach an on-ramp, see that everyone is already following at the minimum following distance, and just sit there and wait for rush hour to trail off. No, they will wait for the what they feel is the weakest link where they can muscle in and hit the gas. Consequently, most people will feel that their space is about to be threatened and close the distance with the car ahead of them to prevent the interloper from cutting in front of them.

You wrote, "You're saying drivers will crowd on anyway causing a jam, hence my description of poor driving habits."

It's actually called human nature and in the end you (and engineers designing roadways) must account for it. In fact, engineers use Nash equilibria (John Nash's game theory) to optimize roadway traffic. The solution set used is not necessarily the best for a group that is cooperating fully. However, the use of Nash equilibria improves the net traffic flow in real-worl conditions.

There are a number of psychological papers written on the subject of how people react in groups and how they choose what is advantages for the group versus what is advantageous for the individual by unilateral action.

Both choices have advantages, but not universally in all situations. In other words, it does not benefit the group for individuals to only act in the group's best interest all of the time. Conversely, it is not always best to act unilaterally all of the time.

All life forms are genetically programmed to work in this fashion to one degree or another. So, while people have varying abilities to cognitively override this genetic programming you still have to account for it as a general rule and remember it is based on a survival instinct.

Simply labeling it as poor driving habits will not produce the best results. You are over simplifying the effect. The whole thing is much more convoluted than that and unless you account for behavior your roadway solutions will always be sub-optimal.

Okay and having utilized these roadways 1+ million miles I did notice a distinct in traffic when the cell phone was introduced. Without the necessary attention or focus upon this driving task much roadway design criteria not withstanding all is moot without specific control devices to fill the gap. This human nature trait as you've described also is fitting in greed scenario's we've witnessed on the street but call it what it is, negligence/reckless or simply cause and effect.

Good driving habits include increasing the nominal distance when conditions require but less is considered dangerous. Perspectives are skewed when we try to get ours first. My intentions in traffic are to keep moving but I'll attempt to allow others to continue moving past me; then I never get jammed. Ya know if you spend anytime pouring liquid from gallon jugs you know letting it chug takes longer than a steady pour allowing air to flow too. An elderly Chinese woman had two large pots, each hung on the ends of a pole which she carried across her neck. One of the pots had a crack in it while the other pot was perfect and always delivered a full portion of water. At the end of the long walks from the stream to the house the cracked pot arrived only half full. For a full two years this went on daily, with the woman bringing home only one and one half pots of water. Of course the perfect pot was proud of its accomplishments. But the poor cracked pot was ashamed of its own imperfection, and miserable that it could only do half of what it was made to do. After two years of what it perceived to be bitter failure, it spoke to the woman one day by the stream. 'I am ashamed of myself because this crack in my side causes water to leak out all the way back to your house.' The old woman smiled, 'Did you notice that there are flowers on your side of the path, but not on the other pot's side?' Thats because I have always known about your flaw, so your side of the path, and everyday while we walk back you water them.' 'For two years I've been able to pick these beautiful flowers and decorate the table.' 'Without you being just the way you are, there would not be this beauty to grace the house.' Each of us has our own unique flaw. But it's the cracks and flaws we each have that make our lives together so interesting and rewarding. You've just got to take each person for what they are and look for the good in them. So, to all my cracked pot friends, have a great day and remember to smell the flowers on your side of the path!

Nice parable. I liked it. :-)

Agreed bwire. I think a lot of the serious jams can be alleviated simply by people backing off, and giving everyone around plenty of room to merge and change lanes. I don't think it would end traffic slow downs, but it should keep traffic from coming to a dead stop. As for the accordion effect, it seems this is compounded by vehicles packed too closely together. If there was plenty of space between vehicles the accordion would be more elastic.

Agreed bwire. I think a lot of the serious jams can be alleviated simply by people backing off, and giving everyone around plenty of room to merge and change lanes.

Occam's razor.

I like to think so, but I doubt it, I agree with what AH mentioned the traffic flow is complex, and where the problem shows itself is not at the origin.

Not sure how Occam's razor applies here. I think that in this case as a large system dynamic, the individual components can effect the whole system through individual behavior modifications. Versus the idea of macro adjusting the whole system to compensate for the behavior of all the components.

It seems that traffic flow is very interesting study in the coupling between system dynamics and human behavior.

It's definitely worse when a 'critical number' in the mix, have no manners and a 'me first' attitude. You see this in some cities more than others - not just American ones.

It seems to work best when ego's and arrogance are 'suspended' and 'play fair' is engaged, whilst driving.

that's not nice talking about the french that way.

Not sure how Occam's razor applies here.

from this

I think a lot of the serious jams can be alleviated simply by people backing off,

and it can't, because people misunderstand Occam's razor "The principle is often incorrectly summarized as "the simplest explanation is more likely the correct one". This summary is misleading, however, since the principle is actually focused on shifting the burden of proof in discussions"

And frankly, I don't believe there is nothing simple about it.

Although your last statement is in line with that.

It seems that traffic flow is very interesting study in the coupling between system dynamics and human behavior.

I didn't know there was a proof with which to contend, only speculation and assumption. My assumptions are limited to serious traffic jams and not traffic in general. Short of launching a public service campaign to get every driver to back off and give each other space I have no way to prove anything. It is simply what I see within the system dynamic. I will contend that a public service campaign is cheaper than building more and more, wider and wider roads.

Do you drive?

Because--just because--and please simply think about it (in conjunction with several of the posts herein).

I'm not sure that people's driving habits is determined by human nature. That aside I do drive and the 2 second rule was part of the California Driver's Handbook. I feel it it is too short a distance and I give 2 or 3 times (or more) that distance when driving. The 2 (or more) car length supposition is about allowing lanes to merge when traffic is moving very slowly... it is a minimum baseline. Typically when vehicles are stopped (or approaching stopping speed) in traffic they leave no space (very little) between bumpers which further congests traffic if one lane needs to merge into another.

This is a waste of time. Bye.

There is a fascinating effect that happens here in Arkansas that I haven't seen elsewhere. (I've lived in Colorado, New York, and Florida)

Here's the short... 2 lanes (each direction) widening to 3 (no on ramps, only full speed off ramps; I've never seen them back up). I can be cruising along the 2 lane just fine 65 mph, hit the 3 lane and have to slow to stop and go traffic. No rubber neckers, no accidents, nothing at all to note. Then eventually it all picks back up. Everything I have learned about traffic in school says there should be an increase in the level of service and yet it drops.

Talking with the locals about it, no one has a reason beyond "its a curse from the farmer who's land is now divided by the highway."

what type of off ramps. Cloverleaf interfers off ramp with the people trying to get to the on ramp and merge

I don't remember the term for them, but unlike cloverleafs they are the "full speed" designs. The highway has one exit (i.e. no merging, in fact the split expands the road further to 4 lanes, 3 continuing on and 1 exit only). That's why the whole thing boggles me... the road is losing traffic volume, speed limit is unchanged, design capacity is increased, yet the level of service goes down.

Is there a 'fear factor' - like reduced visibility or incoming traffic is seen as 'too close'?

Off the cuff, I'm thinking no, but I hadn't considered that. I'll have to pay a bit more attention to that on the way to the office tomorrow.

You are all missing the point. The less space I leave between me and the car in front of me the safer I am. If for example I leave 2 seconds, and he slams on his brakes what difference in velocity will there be after I close that 2 second gap. Where as if I leave only 1 second the difference in velocity will only be half as much so I will only suffer half the damage and injury .....right? I mean hell if I left a good 7 or 8 seconds the guy will be at a dead stop by the time I hit him and then I'm really in for it.

All of the above of course asumes I am reading or replying to an interesting CR4 post while driving and that I don't intend to hit my brakes at all.

So, the safest place to be is actually in contact with the guy in front of you, right. Then, there'd be no impact at all, just a gentle deceleration, until you tapped your brakes and decoupled.

The purists will whine, but how can anyone argue with your logic? GA!

And if the I and the fool in front of me slide into the level train crossing and get whacked? I'm gonna sue him for having such lousey brakes that he almost got me killed!

and the guy behind you is in contact with you....then everyone can do the locomotion. : )

I can see that very few of you, if any, have driven in convoy, if you had, you would know that set distances are impossible if you want to go anywhere.

Consider a number of vehicles in military convoy, as you approach a turn, the lead vehicle slows, the next vehicle slows on seeing brake lights; this ripples back till the last vehicle has slowed, but well back from the turn. The first vehicle, as it straightens up, accelerates to convoy speed, opening a gap to the second vehicle, running at convoy speed while the second vehicle accelerates to greater than convoy speed to catch up, opening an even longer gap to the third vehicle, and so on until the last one is breaking the law so as to catch up. It would be nice if the convoy leader adjusted the accelerations to help the trailing vehicles, but that would slow the progress of the convoy, resulting in a verbal shellacking of the leader by the brass. I have been a convoy leader.

Now, instead of the convoy, think of private vehicles, each with slightly different comfort speeds and you will see that, unless and until, roads are straight and free of obstacles and drivers all drive at the same speed, there will be bunching.

military convoys......you watching movies. These convoys are spread out, but moving.... I.e. Floored. But that isn't saying much

That's much too cryptic for me, perhaps I'm dense.

I used the convoy as a device, it is a group of vehicles trying to maintain the same average speed, but it can only do so by exceeding it as long as there is any impediment in the road. I then wanted to draw attention to the added difficulty when the vehicles are not trying to maintain one speed.

The convoys I led were a long time ago, while on headquarters and signals exercises, on night time runs on the back roads of Germany, vehicles blacked out as in war. The process is exacerbated in those conditions, but it does not go away in daylight.

Maintaining a safe following distance is an idea and if an attempt is made to accomplish it flow is enabled but when the ideal is discarded a jam surely follow. You can see this occur even when traffic is very light but several vehicles get to close together when exiting an a minor jam will occur.

See also the kids' game "Crack the Whip" for an example of nonlinear behavior.

Probably not permitted now. Add it to Kramarat's "Too Much Safety" thread.