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Old October 19th, 2008, 07:53 AM   #1
Scion
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Reseach on cause of traffic congestion

This shows a "shockwave traffic jam" where the congestion just happens for no apparent reason.

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Old October 19th, 2008, 10:05 AM   #2
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It's an interesting video. However, with this investigation the results were no surprise for me. I mean, I see jams enough to know this
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Old October 19th, 2008, 10:19 AM   #3
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Interesting video. Did they ever find a solution? It's interesting to know it takes one car to **** up the flow of a freeway. I remember once I had to stop because a car in front of me suddenly blew a tire and stopped in the middle of the freeway blocking two out of the three lanes, I only stopped for about 15 seconds but noticed how the entire freeway backed up behind me.
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Old October 19th, 2008, 11:01 AM   #4
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Well, if it's busy it can go very fast. I once saw an accident happening in Denmark (I think it was Odense-Copenhagen) on the other lane and I was amazed how quickly everything stopped on the other side.
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Old October 19th, 2008, 12:26 PM   #5
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That's because you can't possibly drive at the exact same speed. If you let the car drive without hitting the gas, some cars slow down faster than others.

However, this is only one side of the traffic jam (too much traffic on a lane). Other traffic jams start because of merging traffic at an already filled-to-capacity freeway. The solution in those situation could be ramp meters. Minneapolis has over 400 of them.
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Old October 19th, 2008, 03:28 PM   #6
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In 2000, MN/DOT, which is the state of Minnesota's department of transportation, conducted an experiment in the Minneapolis area where they actually shut off the ramp meters for I'm not sure if it was two weeks or a month and found that commute times increased by as much as 20% and I believe accidents were up as well. The reason for the study was that one of the state senators wanted "proof" that they worked. Apparently, people were complaining about some of the wait times at the meters, which in some cases was as much as 15 to 20 minutes. MN/DOT was keeping so many cars backed up at meters because most of the freeways in the area are only 4 or 6 lanes and many are also outdated in design. For instance, one interchange with I 35w and I 494 near the Mall of America in Bloomington is a simple cloverleaf without C/D ramps that handles 250,000 cars a day and has the most accidents in Minneapolis. They are reconstructing that one starting I believe 2012, but there are a lot of other problem spots. Well, stats don't lie and it was proven in the study that indeed ramp meters do work to decrease commute times and increase traffic flow in most situations. The state did remove some meters that were not needed per the study and decreased the wait times at the ramp meters to a maximum of 5 minutes.
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Old October 20th, 2008, 12:47 AM   #7
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This is already common knowledge. Sometimes called 'phantom jams' in the UK, they start when one person brakes a bit too hard, causing the block up.

In the Uk and no doubt everywhere else when this happens the speed limit behind the jam is lowered with the use of the overhead electronic signs turning on. The idea is that the cars approaching the phantom jam go a bit slower hopefully, allowing the jam to dissapear. Unfortunately in most of the UK the overhead signs only display an advisory speed limit (without the red circle around them). Some areas now have enforcable limits now which can more effectively remove these traffic jams.

They can often be frustrating for drivers who see the speed limit signs of 50 or so and saying 'queue ahead', but then never encounter a queue, but what they dont realise is that the limit is on to eradicate the queue, or at least thats the idea.
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Old October 20th, 2008, 09:26 AM   #8
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Those overheads in the Netherlands with electronic speed limits, are a bit different than in the UK then... We explicity don't want an enforcable speed limit because the electronic signs are meant to be a warning and to ease the flow so people can brake easy.

For instance if traffic starts to jam, the overheads go to 70 and then to 50, depending on flow. 50 is the lowest possible. As soon as traffic starts to flow faster than 50, they go back to 70 again. Therefore, it's needed that the electronic signs are not an explicit speed limit, but an advisory speed limit.
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Old October 21st, 2008, 12:58 AM   #9
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Yeh 90% of them are advisory. But some of the newer ones are for areas with complete congestion to work more effectively.
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