Interesting article in New Scientist this week. They have finally managed to demonstrate the shockwave propagation of a traffic jam.
Apparently this was a theory developed years ago to explain why jams form on roads that are free flowing but at their capacity.
tinyurl.com/2weqk9
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demonstrate the shockwave propagation of a traffic jam.
Interesting that it took someone so long to come up with a "laboratory" demo of the real life situation.
As the comments on that article say, it is down to the ordinary humans inability to fine control their throttle/speed response. (Extra-ordinary humans such racing drivers and racing cyclists are examples of people who can maintain steady speeds in jams that look like they are all a joined up long train).
I have experience of being a passenger when a particularly "bad" driver is in charge. He just cannot apply fine control and maintain a steady speed. So even in a free flowing traffic, he tends to catch up with the car in front, gets very close, then he brakes to build up a safe distance, then he speeds up again, and this cycle repeats all the time.
One day I asked him why he did this, and he said he just could not control his foot to set the pedal at a steady level in order to maintain a steady speed. He demonstrated this to me while stationary in a car park - he could not press the pedal slightly to achieve a constant 2000 rpm speed. It would keep rising beyond that, he would then lift off, revs would ease, he would then reapply pressure on the pedal.
On the other hand I have been a passenger with a driver who is so good at observing the conditions, and his driving is so smooth, that he rarely has to use the brakes in free flowing traffic.
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" On the other hand I have been a passenger with a driver who is so good at observing the conditions, and his driving is so smooth, that he rarely has to use the brakes in free flowing traffic."
I never saw you in the back of my car jbif. ( 52000 miles so far and original brake pads all round.)
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On an entirely personal note & prime reason why I'd never make a good Buddhist - I cannot abide or have the slightest compassion with drivers who constantly accelerate & brake for no good reason other than lack of skill and/or disinterest in acquiring it. I'd even say I prefer 'skillful' tailgaters or aggressive white-van-persons to the steering wheel clenchers who are so inept they constantly yo-yo in your rear-view mirror. Rant over - thanks for listening!
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"I cannot abide or have the slightest compassion with drivers who constantly accelerate & brake for no good reason other than lack of skill and/or disinterest in acquiring it."
Aren't they just particularly delightful when you're using cruise control. Nothing ruins a long distance journey more than having one of these idiots buzzing around you - overtaking you, slowing down, getting under your feet. Makes me mad thinking about them.
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Whilst this may be a 'first' using real cars, a mathematical model has been used for some time and has been discussed here several times.
Has all ther marks of a student project, altho the research into the underlying psychology may reveal something new.
Alternative investigations to include could be;
get the volunteers to drive for 48 hrs without a rest, to see how the frequency of misjudgments increase.
introduce rubber necking diversions - to trigger the effect.
It would also be interesting to see if in the closed loop enviroment it is possible for the wave to disappear. I would guess that you would need to increase the size of the circle and fit the drivers with blinkers and neckbraces so thay could only see straight ahead.
Look at
www.traffic-simulation.de
and play some games without ending in an expensive pile of scrap metal.
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It's an interesting observation that there are people who are simply physically unable to maintain a constant engine speed.
But there seem to be other triggers that cause drivers to abandon constant flow and switch to stop-start mode. I encountered a good example coming in to work today. I was on a reasonably spaced ordinary A road, all the traffic maintaining a reasonably constant 50 - 60 mph as we negotiated slight bends, hills, etc. I could see in my mirror in the distance a car that was likewise following at the same speed, keeping a distance of about 1/4 mile.
Then it was as if he suddenly woke up and realised there was a car ahead (me), and quite rapidly closed the gap. After alternately tailgating, then dropping back, he finally managed to overtake me and the next car, but had to pull in sharply and was flashed by an oncoming lorry. The result was a ripple of braking and gap-closing down the line, until it all settled down again. there were no more overtaking opportunities, and the car once more settled down to the same speed as the rest of us.
At journey's end he was 3 cars ahead, having achieved nothing except create a momentary moving jam, at the cost of one somewhat dangerous overtaking manoeuvre.
So whereas he probably arrived at work fuming about the slow state of the road, I arrived thinking that was a good run, shame about the brief jam. But we had each had covered the same distance in the same time.
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shockwave propagation
Interesting. I've always called this "caterpillaring", which I think is more descriptive.
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