I've been down too many highways where all two or three lanes were occupied by people doing the speed limit or slower. Nobody could pass them since they were all near each other with no room to get around.
The result? Traffic gets backed up needlessly and transit time increases.
This is often one of the reasons why we have minimum speed limits. You are simply an impediment to traffic if you go slow.
I'm a transportation planner, and the great grandparent is incorrect. Slower speed has little to do with congestion, other than being a side effect. Up to a certain point, slower speeds actually allow more people onto the road. Congestion just has to do with the number of vehicles being too great for the amount of road, for the most part. Speed and capacity are related, but only in that speeds drop as congestion increases.
You're just talking about the situation where someone is blocking you from driving as fast as you want to. That's just life.;)
I don't know if that is an official term (probably not) but it's what I call it. Say you are stopped at a redlight, you and a line of cars. Light turns green. You can see the light change, but you can't go yet, you have to WAIT for the person in front of you to get going, and on up the line. it's nutz! People are looking at the back of the car in front of them, waiting for that car to move. You can see it happen, lead car gets going, then the next, then the next, etc., ie, the centipede effect. The result i
The result is a huge waste of time at a limited green interval just getting back up to speed, whereas if everyone looked at the light and just went, it would allow faster and more coordinated acceleration and smoother traffic flow.
And everyone would be tailgating the guy in front of them. A fender bender at any point in the line would propagate back through more cars causing more property damage. But, that would be one less red light for someone to wait I guess.
Ah yes, the "if only everyone would step on it when the light turns green" falacy. I'd normally use harsh language at this point, but for the fact that I was the same [expletive deleted] as you, not too long ago. Here's the deal:
When you're driving at speed, you maintain distance X from the car ahead. And, when you end up at the end of a line of cars at a stoplight, I'll bet dollars to doughnuts that you close to within X/20 of the car ahead. Once the light turns green, the safety margin you and everyone el
When a situation evolves when someone needs to make a quick brake/accelerate/maneuver decision, the quickest reaction is to step on it, which won't respond
While I do not know the system deployed here, the other system I have seen (a Swedish, I believe) worked so that if you stepped on it, the system would automatically deactivate and allow the driver to accelerate.
I'm a transportation planner, and the great grandparent is incorrect.
Just saying "I'm a transportation planner" means absolutely nothing to us unless you can tell us which city you work for, and which roadways you've planned.
If you've planned some of the roads near where I live, I'd take whatever you say with a large grain of salt.
> Go a few miles slower and the traffic will be more "smooth" > and global highway capacity will increase: the net effect will > be that more cars wil go over a milestone on a time frame, and > contrary to common sense everybody will arrive faster to their > destinies.
The slower the cars are travelling, the less distance required between each car, therefore the higher number of cars that can be on the road at the same time, therefore the increased capacity of the road..
The problem (of course) is that it assumes that all the cars are travelling the same speed.
Most traffic collisions result from cars travelling different speeds. One car goes much faster (or slower) than the rest causes an accident.
Or (following the line of reasoning present in the preceeding two posts) we could make the speed limit on every road 5KPH, which would maximize the road capacity!
Hopefully, once this system is installed in all cars, it can also be used to ensure people don't 'slow' (the opposite of speed?).
I have seen so many instances of these pathetic people doing under the speed limit for no reason other than they *think* they are being safer. However, the congestion and frustration they cause behind them lead to many incidents.
Obviously it will be a lot harder to implement a device that makes you travel faster due to the requirement to determine obstacles. But it needs to be
Obviously, speed and carrying capacity are correlated...
I mean, it's not like drivers going 80MPH are going to be directly on eachother's asses--although I have to admit some are. If drivers follow the 1 car length/10 MPH rule--or the 3 second rule, then cars will be spaced much farther apart at higher speeds. Finding the highest throughput at the highest speed assuming certian condidions should be a easy enough to find.
That said, I've known several factors to increase the liklihood of congestion--I'm
You're right to some degree, about predicting traffic flow being damn hard (I run traffic models for a living). There's a whole variety of software for predicting traffic at different levels of detail, from fairly coarse models of a region down to simulations that model individual vehicles (including driver behaviour etc). Unfortunately the very detailed models require huge amounts of data (intersection geometry etc..) and are impractical for modelling whole cities.
Basically there's no way of modelling en
I read an article a few years back where ADDING routes for traffic to take actually added to congestion in some cases.
This one city had two basic routs between points a lot of traffic went through and to ease congestion they ran a third road. Congestion went up. After doing some math they realized the problem and made the new road not through and congestion went back down.
Wish I could rember why that worked that way (and no it wasn't grandma/bubba/blondie getting confused over which way to go and p
Vehicle speed is like ping times. Road capacity (vehicles per hour) is like network capacity (mbps). When a site gets slashdotted, ping times go way up. During rush hour, it takes forever to drive anywhere. Same idea, basically.
As for effect of speed or speed limits on road capacity: if you want to download your mp3s faster, you don't look for an isp with better ping times. You get a higher capacity connection. Similarly, if you want to get more cars into the city per hour, you don't raise the speed
I'm guessing that the speed reductions on the M25 that frequently occur at peak time with no obvious reason are just to reduce traffic speed to reduce congestion? Could be wrong though...
You're correct - the loops under the road ahead detect a body of congested traffic and attempt to 'smooth' the flow by reducing the speed of the traffic approaching it from behind. I think the hope is that the effect of the back-propagating wave that's produced when people start braking more and more sharply (until they come to a standstill, if it's really bad) having encountered a body of slower moving traffic (lorries overtaking each other at 0.1mph, for example) can be reduced.
"Who alone has reason to *lie himself out* of actuality? He who *suffers*
from it."
-- Friedrich Nietzsche
Doesn't slower speed increase congestion? (Score:2, Funny)
Re:Doesn't slower speed increase congestion? (Score:0)
This is one of those cases. If traffic was a liquid flowing smoothly through a pipe, then it would be. But traffic does not behave like a liquid.
Re:Doesn't slower speed increase congestion? (Score:0)
I've been down too many highways where all two or three lanes were occupied by people doing the speed limit or slower. Nobody could pass them since they were all near each other with no room to get around.
The result? Traffic gets backed up needlessly and transit time increases.
This is often one of the reasons why we have minimum speed limits. You are simply an impediment to traffic if you go slow.
Re:Doesn't slower speed increase congestion? (Score:4, Informative)
centipede effect (Score:2, Insightful)
Re:centipede effect (Score:2)
And everyone would be tailgating the guy in front of them. A fender bender at any point in the line would propagate back through more cars causing more property damage. But, that would be one less red light for someone to wait I guess.
Traffic gets compressed at a red light. It
Centipede effects: Spending Your Safety Margin (Score:3, Interesting)
When you're driving at speed, you maintain distance X from the car ahead. And, when you end up at the end of a line of cars at a stoplight, I'll bet dollars to doughnuts that you close to within X/20 of the car ahead. Once the light turns green, the safety margin you and everyone el
Re:Centipede effects: Spending Your Safety Margin (Score:2)
While I do not know the system deployed here, the other system I have seen (a Swedish, I believe) worked so that if you stepped on it, the system would automatically deactivate and allow the driver to accelerate.
Re:Doesn't slower speed increase congestion? (Score:3, Funny)
Just saying "I'm a transportation planner" means absolutely nothing to us unless you can tell us which city you work for, and which roadways you've planned.
If you've planned some of the roads near where I live, I'd take whatever you say with a large grain of salt.
Re:Doesn't slower speed increase congestion? (Score:1)
> and global highway capacity will increase: the net effect will
> be that more cars wil go over a milestone on a time frame, and
> contrary to common sense everybody will arrive faster to their
> destinies.
The slower the cars are travelling, the less distance required between each car, therefore the higher number of cars that can be on the road at the same time, therefore the increased capacity of the road..
THAT seems common sense t
Re:Doesn't slower speed increase congestion? (Score:2)
Most traffic collisions result from cars travelling different speeds. One car goes much faster (or slower) than the rest causes an accident.
Or (following the line of reasoning present in the preceeding two posts) we could make the speed limit on every road 5KPH, which would maximize the road capacity!
Re:Doesn't slower speed increase congestion? (Score:1)
I have seen so many instances of these pathetic people doing under the speed limit for no reason other than they *think* they are being safer. However, the congestion and frustration they cause behind them lead to many incidents.
Obviously it will be a lot harder to implement a device that makes you travel faster due to the requirement to determine obstacles. But it needs to be
Re:Doesn't slower speed increase congestion? (Score:1)
I mean, it's not like drivers going 80MPH are going to be directly on eachother's asses--although I have to admit some are. If drivers follow the 1 car length/10 MPH rule--or the 3 second rule, then cars will be spaced much farther apart at higher speeds. Finding the highest throughput at the highest speed assuming certian condidions should be a easy enough to find.
That said, I've known several factors to increase the liklihood of congestion--I'm
Re:Doesn't slower speed increase congestion? (Score:1)
Re:Doesn't slower speed increase congestion? (Score:2)
This one city had two basic routs between points a lot of traffic went through and to ease congestion they ran a third road. Congestion went up. After doing some math they realized the problem and made the new road not through and congestion went back down.
Wish I could rember why that worked that way (and no it wasn't grandma/bubba/blondie getting confused over which way to go and p
Translation for computer people: (Score:2)
As for effect of speed or speed limits on road capacity: if you want to download your mp3s faster, you don't look for an isp with better ping times. You get a higher capacity connection. Similarly, if you want to get more cars into the city per hour, you don't raise the speed
Re:Doesn't slower speed increase congestion? (Score:2)
Re:Doesn't slower speed increase congestion? (Score:1)