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Math Says You're Driving Wrong and It's Slowing Us All Down (wired.com)
A new study in IEEE Transactions on Intelligent Transportation Systems mathematically suggests that if you and everyone else on the road kept an equal distance between the cars ahead and behind, traffic would move twice as quickly. From a report: Now sure, you're probably not going to convince everyone on the road to do that. Still, the finding could be a simple yet powerful way to optimize semi-autonomous cars long before the fully self-driving car of tomorrow arrives. Traffic is perhaps the world's most infuriating example of what's known as an emergent property. Meaning, lots of individual things forming together to create something more complex. Emergent properties are usually quite astounding. You've probably seen video of starlings forming a murmuration, a great shifting blob of thousands upon thousands of birds. Bats flying en masse out of a cave is another example, swarming sometimes by the millions through a small exit. And scientists are just beginning to understand how they do so.
I was trying to get from the Domestic to the International terminal, about 5km, in a cab (along with wife and luggage). The lightrail system was under construction, which added to the mess. Traffic was gridlocked until about midnight, when it started moving. Turns out there was one traffic light that caused the gridlock. Once that went to flashing yellow, the drivers negotiated their way through the intersection.
than getting stuck behind a driver that keeps racing up to the car in front of them and then hitting the brakes, falling back and doing it all over again. Keep it steady man.
if you and everyone else on the road kept an equal distance between the cars ahead and behind, traffic would move twice as quickly.
Yes, because no one would be merging into traffic anymore.
If everyone kept an equal distance and followed a standard merging pattern of every other car, then it would likely solve the merging problem as well. Long ago we were shuffling decks of cards in a much less practical and inefficient way until certain physical moves were found to increase that efficiency ten-fold.
It's also well-known that impatience creates stop-and-go traffic patterns, which is but one of the many human factors that autonomous solutions will be looking to solve.
Common sense says we don't need math to show what is slowing down traffic. Maintaining distance really means matching speed, acceleration, and deceleration. If those happen distance itself becomes less of a key factor. Added distance is just an aid for drivers who aren't good at staying with traffic flow.
If you want traffic improvement,
1) get left lane laggards to drive properly and not slow down faster traffic
2) get everyone to be expeditious when intersection lights turn green
3) teach people not to contribute to traffic compression waves by over decelerating and then under accelerating
Oh, my, some student has handed in his "study" and it made the papers. The next study that debunks it, probably won't so everyone will keep believing this one. Like that old "study" that said 80 km/h was the ideal speed for max throughput (it's not).
They probably did a simulation where all cars were following the same algorithm. Which only works if, you guessed it, all cars are using the same algorithm. Otherwise, only a huge mess results.
I can see so many things wrong with this. For starters, if I understood correctly, when somebody tailgates me, I should tailgate the car in front of me as well so we keep an equal distance? Great way to cause pile-ups when one car starts to brake. (Been in one of those myself, I could stop just in time, so could the car behind me, but the three cars further back slammed us all together, fortunately there was a dashcam).
So we're back to a minimum safe distance between me and the car in front, which is what I normally do. Now, if the car behind me is further back, according to the "study", I should slow down to increase my distance in front and reduce my distance behind. But then of course the car behind me is going to slow again to get back to its old distance, so I keep slowing until I have as much distance in front of me as the car behind me. Now the car in front of me is going to slow down to as well, because he wants as much distance in front of him as behind him. I don't exactly see throughput improving here...
Max throughput is achieved if cars simply keep the shortest safe distance, allowing for small fluctuations in distance to keep speed as constant as possible. And yes, indeed, very few drivers actually do that.
That's not surprising. Spread cars out too much and you reduce the roadway's capacity. Put them too close together and you have to slow down to accommodate the driver's minimal reaction time. Having every driver choose his own distance means you can have both effects simultaneously: wasted space and insufficient response time.
Put all these constraints on and it seems obvious that you want to space cars uniformly with the minimal distance consistent with whatever statistical level of safety you demand. Naturally robotic systems will be more efficient since they require less response time -- in fact they can react to events that will cause the car in front to slow.
What would be interesting is to see the exact results they came up with: how far for how fast and under what conditions? What are the significant input parameters of the model? For example I'm sure varying the acceptable probability of a crash has a powerful effect on the optimal distance.
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Hey! You're fit to work for governement with that mentality.
Sunny day, empty 6 lane highway... 45 mph. Sure. "Safety first" right ?
"Not to mention all the idiots who use words like boxen."
Anonymous Coward on Monday August 04, @06:49PM
If everyone is accelerating when the car behind them gets closer all it takes is one tailgating asshole to produce a multiple car collision hasard of cars driving too close together.
Don't drive closer to the car in front of you than security dictates, even if there is a tailgater behind you.
Democracy is a sheep and two wolves deciding what to have for lunch. Freedom is a well armed sheep contesting the issue
Don't drive closer to the car in front of you than security dictates, even if there is a tailgater behind you.
You should do exactly the opposite. If someone tailgates you, leave more distance in front of you so you can afford to brake slowly, giving the person behind you more warning time.
Isn't that what NASCAR is anyway? Between the wrecks and such,...
Just set your Tesla (or other modern) adaptive cruise control to, say, five car lengths, and just steer. It is far far easier than having to brake/accelerate and the hardware watches even when the driver has zoned out. No worries about hitting the idiot in front. No worries if someone merges into your lane: the car adapts.
And a slight speed adjustment allows the distance to return to normal after the merge
The problem is that a road runs at maximum capacity when speed is high and distance is minimal. A slight speed adjustment, like you suggested, has the effect of decreasing maximum road capacity.
That means that the road after the merge point not only has to deal with more cars, but also with a lower capacity to carry those cars. This lower capacity will propagate backwards to the road before the merge point. And that's how you end up with a traffic jam.
That will help solve the traffic problem too.
Which also takes us into arguments of age and experience. The youngest drivers usually have the best reaction time but may not necessarily make the best choices prior to needing to use that reaction time. The oldest drivers have the most experience with what traffic conditions are to be like but may have very poor reaction times. The sweet-spot is kind of hard to calculate but probably biases toward a youngish driver that has figured out traffic conditions but still has fast reaction times.
When I read the article summary it sounds like they want our cars to operate like trains, which all maintain the same distance (on account of mechanical coupling) and all go the exact same speed (again, mechanical coupling). Trouble is, with cars everyone has different destinations and therefore won't maintain the same speed. Cars slow to turn-off. Cars must enter the right-of-way. Not all drivers are driving for the same reason either, some enjoy driving performance vehicles, using that quick acceleration to get up to speed whenever they can, while others drive much more gently.
The argument for us all driving an exactly particular way rings of the spherical cows in a vacuum solution to a farming problem. Isn't going to work in real-world applications.
Do not look into laser with remaining eye.
That's why we have metered on-ramps. They limit the number of cars that have to weave into the traffic. And if traffic on the freeway starts to slow down, so should the metering rate until the bottleneck relieves itself.
But if metering were actually implemented this way, people waiting would go insane. And it doesn't account for the carpool bypass, which ends up jamming traffic at the merge point anyway. In reality, ramp metering has become a penalty* for solo drivers, nothing more.
*Unless you are fortunate enough to live in a wealthy neighborhood and can call your state representative to keep metering off your own little local on-ramp. Why the hell do rich people get their own on-ramps anyway?
Have gnu, will travel.
Slow traffic is caused by trying to put more cars on a stretch of road than it can handle.
True in many but not all cases. If you increase throughput by managing congestion, you reduce the number of cars on the road at a given time.
Master of the obvious. Armies have known this for millennia. That's why soldiers maintain fixed distance and all start out together with a "forward...march" command and stop with a "company...halt". Try that at the next traffic light when you are 5 cars back. Man, if everyone just all went at the same time when the light turned green it would be awesome, but without an automated system it's just a 4 car pile-up.
With human drivers you inevitably get the "slinky" effect due to reaction time and differences in preferred speed and follow distance.
Exactly. Overall traffic flow seems most efficient if traffic on main routes is bunched into "packets" of vehicles with gaps between packets large (long) enough to allow traffic from smaller routes to enter or merge onto the main route. My home town did this with updated lights and sensors about thirty years ago (!). Once on the main road you never had to be stuck at a light until all reaching the next town.
I believe this will eventually become the force driving the adoption of self-driving technology. When we get to the point autonomous cars do it right and are mixed in with human-driven cars that are screwing up and slowing down the traffic pattern for everyone else. I can see the current driving model being totally turned on its head with commuters eventually demanding that we ban human drivers.
There will also be economic pressure. Human drivers need signs, lights, and a weighty infrastructure investment. Autonomous cars need none of that expensive support.
That's our life, the big wheel of shit. - The Fat Man, Blue Tango Salvage
How am I supposed to do all that shit when I've committed 96% of my attention to my iPhone?
Beware of the Leopard.
*Unless you are fortunate enough to live in a wealthy neighborhood and can call your state representative to keep metering off your own little local on-ramp. Why the hell do rich people get their own on-ramps anyway?
I believe this is because it routes their traffic, the type that doesn't care about others off of the same roads of the less fortunate and people that have to actually pay attention so their vehicle doesn't get totaled by the person having a conference call in their luxury SUV with 40% visibility not paying attention to the road.
Living in Las Vegas. I have noticed that the majority of the accidents around the valley are high end or fresh off the lot vehicles. While me in my old pickup truck, has never even been in an accident because I don't tailgate, I don't speed unless the freeway is almost empty. And I actually look around me when im going to move my vehicle out of its traveling lane! It's a hell of a concept.
The sweet spot is well known - it's around 50-60. That's why insurance companies offer people in that age bracket the lowest rates - they have the fewest accidents.
Brake lights cause traffic jams. If you're on a motorway (freeway), never use your brake pedal except in an emergency. That's what engine braking (or regenerative braking on modern cars) is for. Keeping a steady speed, and only accelerating and decelerating slowly helps other drivers to match speed when merging, it also does wonders for fuel economy.
Meh, I don't think it'll get much better than today. Commute driving is a solid mix of people who are either:
a) Late, stressed and glued to the rear bumper in front of them
b) Bored, zoned out and mentally passing the time with something else
It's human nature that you'll have a huge variation in reaction time and aggressiveness to close the gaps. I have a good view of that near work, due to a slope, bridge and intersection on the other side you can see probably 30-40 cars at once at rush hour. You see the green light and can count like 1-2-3-4-5 cars getting in motion, the first 20 or so will be on the bridge and mostly just see the car in front of them. In a drill you could have great performance, same way you can evacuate a jumbo jet in less than 90 seconds. In practice you can see the gaps and the snake buckling.
Once we have all have (semi-)autonomous cars I expect this will look more like a train with invisible couplings rolling out of the station, the car just has to keep a minimum safe distance but this is exactly the kind of micromanagement computers excel at. I don't think you even have to do anything in particular to make it happen, all you need is extreme consistency and it comes pretty much free. Maybe you can optimize it further but I think 95% of the gains come from simply moving the instant it's safe to do so.
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Actually the biggest impediment I've found to merging recently is that most people no longer let you in when you signal. When I learned to drive back in the 1980s, you would signal, the person in the next lane behind you would usually slow down (or at least not speed up), and you would merge into their lane.
Nowadays, I signal and I'd estimate about 80% of the drivers use my signaling as an opportunity to speed up to prevent me from merging in front of them. A slight slowdown to allow someone to merge in front of you is vastly preferable to the person having to slow down almost to a stop before he merges because his merge lane is ending and nobody is letting him merge. When he eventually merges at slow speed, he'll cause a massive backlog behind him compared to if someone had just let him merge at high speed.
This guy figured all that out in detail years ago ...
This is why I always pull into your lane when you try to pass me. You are screwing up the algorithm and I'm fixing it.
Some drink at the fountain of knowledge. Others just gargle.
https://www.youtube.com/watch?...
While that sounds logical, it isn't. In general, road capacity does increase as the speed increases up to about 70 km/h. Above 70km/h, the increased distance to maintain a safe stopping distance becomes a bigger factor and the capacity decreases. Therefore, this plan can work. In fact it does; it is standard practice where I live (the Netherlands) and it really does work (to some extent; road capacity still has its limits...). However, it must be said that that's after a very intensive campaign educating the general public on how to merge.
0x or or snor perron?!
I work in a manufacturing environment, and changing even a handful of people's behavior is so incredibly difficult and costly ("always pick up one orange nut at a time, then the blue nut, don't grab two at once.") that asking everyone to change the way they drive is just ridiculous. You have to change things so that the desired behavior is the easier behavior. For instance, advanced cruise control that adjusts your distance automatically might be a solution. In our plant, if the process says they should do X before Y, then the only way to ensure it actually happens all the time is to prevent Y from happening until there's proof X happened. People just aren't reliable.
"I have never let my schooling interfere with my education." - Mark Twain
So - fewer people on the road, which also reduces congestion. Win-win!
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
So - fewer people on the road, which also reduces congestion. Win-win!
I ride a motorcycle - I'm going to die.
Then again, everyone else is going to die too.
"“Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming "Wow! What a Ride!” - Hunter Thompson
Having experienced family being involved the 21st century version of death, rotting away, demented in a nursing home, as they extract the money from their estate, then you are released from your life of catheters and adult diapers and Airecept that coincidentally ends a little after the bank account is empty - I think I'll keep riding that bike.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
Keeping constant spacing and running at a reasonable speed within a lane may be good. But holding the same speed in adjacent same-direction lanes is very bad.
In driving classes, back in the mid-20th century, we were warned against it. You NEVER were to hold the same speed as a car in an adjacent lane. (About a 5 MPH drift, with leftward lanes faster, was close to ideal.) Judging by the behavior of current drivers on California freeways that lore has apparently been lost.
Some of the issues:
- Adjacent cars form a multi-lane "rolling roadblock". Drivers behind them who wish to travel faster are impeded, collect behind them, and end up "compressed", setting up the conditions for a chain, reaction multicar pileup.
- With an inter-lane drift a driver wishing to pass a slower car soon has an opening to switch lanes and proceed.
- With the slowest lane to the right and increasing speed to the left, merges and exits require less speed change and have better timing margins, long-distance traffic proceeds rapidly with little disturbance, and lane changes are easy. Drivers have the opportunity to rapidly distribute themselves among the lanes and drive at a speed where they're comfortable.
- When driving at the same speed as an adjacent vehicle you increase your risk of collision:
- If you're in a blind spot you STAY in the blind spot for a long time. The window of opportunity for the adjacent driver to happen to make a lane change into you - or into the space immediately in front of you, becomes much larger than if you had a relative drift.
- If you hold relative position the other driver's peripheral-vision motion detector doesn't keep him aware of your presence. After a minute or so you're likely to fall out of his attention. Then, if a sudden traffic situation makes him need to change lanes suddenly (or he just wants to change lanes and forgets to do a recheck), he may swerve into you.
(By the way: The two-way two-lane equivalent of the rolling road-block chain-reaction-collision precursor is the "rat pack", a term of art in traffic engineering. It occurs when the first driver goes slightly over the limit and the second driver won't pass because he doesn't want to risk the necessary speed, but follows too closely for following cars to pass in two single-car hops. Fault is primarily on the second driver.)
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I was in Bangkok a few weeks back, and it occurred to me that people riding motorcycles and scooters in that city probably get places twice as fast as cars, because at every red light, people on two-wheeled vehicles split lanes and move to the front - this appears to be perfectly legal there. Every time a light turns green, there's a flock of motorcycles and scooters at the front of the line, riding until they catch up to the next red light, where they then filter to the front again.
More time on the go, less time standing still. One hell of a recipe for getting somewhere quicker.
Slashdot still doesnâ(TM)t support Unicode after it was added to the HTML standard in 1997.
>This isn't even a new thing to study.
It isn't. When I was at college, a long, long time ago, some friends did a model and simulation of flow breakdown on a highway and showed that it followed exactly the same equations as for coax ethernet (which was the norm at the time).
Knowing these, we can understand that cars behave much like packets in a network when it comes to flow efficiency and the math has all be done. In networks however, we can increase the speed limit and number of lanes until we are at the easy point in the curve. With switched ethernet, everyone gets their own road and the congestion is at the junction.
Maybe that's why Elon Musk took Ted Steven's technically illiterate "Series of Tubes" comments literally and decided to start boring tubes.
I should use this sig to advertise my book ISBN-13 : 978-1501515132.
Elsewhere, when my wife got irked with misbehaving motorcyclists somewhat like this, I told her to just think of them as organ donors.
Yes, because all studies involving the average human should just use your experience and extrapolate that out to the rest of the 7.4 billion people on the planet.
Filtering and splitting is legal all throughout Europe, too - and quite handy. In fact, it's really just banned in the 49 other US States (being legal in California) and Canada. Pretty much everywhere else on the face of the Earth, filtering and lane splitting are the norm.
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
How does having a tailgating car force you closer to the car in front of you? The dumbest thing to do when tailgated is to speed up. In fact, I usually slow down so that if there is an accident (more likely with a tailgater) it will be at a lower speed.
In the UK the sequence is mirror, signal, maneuver. In other words, look to make sure it is clear and safe to move, then signal your intent, then move.
People who signal as a way of "asking" to be let in cause confusion. Are they asking, or are they about to move and cause an accident? If I'm unsure I use my horn, it's the only safe thing to do since the person behind is usually tailgating.
Is it different where you are? Either option would be okay if everyone just agreed on the correct use.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
100 mph is not nearly as dangerous as you make it out to be, especially with modern cars.
I used to race motorcycles and even drag raced both cars and motorcycles, so 100+ mph is no stranger to me. But most people do not have the reflexes to go much over 70. It is pretty simple math distance traveled versus reaction time. At 100 mph, you are travelling around 147 feet per second. That's almost 75 feet in 500 milliseconds.
And there is quite a difference when everyone is going near the same speed and when you are trying to go 100 + on a road where most people are driving at 70. A real pucker string moment when that person you are going 30 MPH faster than pulls out in front of you say 20 feet in front of you.You have less than a half second to react, brake and slow enough to not run into them.
Even way back then, I reserved my faster driving for the proper place. And of someone thinks that driving like that on a roadway where most are diving a lot slower - yeah - they are still idiots.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.