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In addition to increasing the gap, you have to drive steadily, with no braking. This makes you become the most predictable car on the road, people behind you can follow steadily instead of constantly accelerating & braking. This leads to reduced congestion.

This CGP video covers some of this https://www.youtube.com/watch?v=iHzzSao6ypE

⬐ lotsofpulp

There is no steady in high congestion areas with lots of on and off ramps. The rules are nice when there is no congestion and plenty of room to spread out, but the problems are inevitable at rush times or at chokepoints.

⬐ fouc

Not all congestion are created by those chokepoints. It's created because someone at some point hit the brakes, and then cars behind get into a pattern of accelerating & braking constantly until the congestion resolves. Steady driving with lots of gaps helps resolve this faster and prevent congestion in general.

https://www.youtube.com/watch?v=iHzzSao6ypE

CGP Grey: The Simple Solution to Traffic.

https://youtu.be/iHzzSao6ypE

⬐ false-mirror

The ACTUAL Solution to Traffic - A Response to CGP Grey

https://youtu.be/oafm733nI6U

⬐ jacquesm

Trains are fine for inter-city traffic > 20 km or so, below that, if you can, take a bicycle. It is a much better solution than a train for door-to-door.

The video that the above animation is from [1] is about how bad (or alternatively, "selfish") driving behaviors where individuals inch up as close to the car in front of them as quickly as possible (only to have to slam on their brakes) actually lead to worse and slower traffic than if everyone just left a buffer of space in front of them and drove at a moderate pace.

So it's actually a lot more analogous than you'd think.

[1] https://www.youtube.com/watch?v=iHzzSao6ypE

⬐ dataflow

While I do love that video, it has some massive oversights:

- Safety margins requires distance to increase with velocity. i.e. if the light turns green and everyone accelerates together, then you end up with a bunch of cars going at high speeds bumper-to-bumper. This would be clearly undesirable even if everyone could press the gas pedal at the same time. Meaning you'd still want to insert a delay between cars regardless of people's ability to press the gas pedal at the same time. Heck, even with self-driving cars, you'd still want comparable safety margins in case something goes wrong; it's not like self-driving cars result in a perfectly predictable world.

- "Stay the same distance apart from the car behind you and in front of you" ignores the fact that the car behind you might be quite far behind you (if there at all). In reality you probably want to maintain a minimum distance both in front of and behind you, not an identical distance.

- It also fails to show that decongesting a traffic jam by deliberately slowing down (which is what you'd have to do to increase your distance from the car in front of you) will actually result in you getting to your destination more quickly. It's certainly not intuitive for that to be the case.

While I'm not claiming the conclusions would be necessarily wrong if you take these into account, for a viewer that hasn't already done research in this area, it sure doesn't convince them that the conclusions are correct once these are accounted for either.

CGP Gray's simple solution to traffic and good visuals.

https://www.youtube.com/watch?v=iHzzSao6ypE

The real simple solution to traffic is no more monkeys driving cars. Also, implicitly, fully isolate cars from human powered forms of transportation.

⬐ mc32

There is a slight flaw there. It fails to account for vehicle malfunctions (blown tires, running out of power, component failure, roadway debris, etc.) so even with computerized coördination you need to keep a speed determined safe distance from vehicles in front of them. (with reference to the accordion effect of stop and go.)

⬐ mjevans

Accidents will require cleanup services.

Meanwhile self-driving cars can learn of them from the scheduling coordination services and distribute the load among working routes without rubbernecking.

Also https://youtu.be/iHzzSao6ypE

⬐ C14L

Really looking forward to one day being able to sit im a self-driving car that goes at 150+ km/h towards a crowded intersection with other cars crossing left and right at equal speeds, and then just pass the intersection through a tiny gap in the wall of crossing cars. Because all those cars talk to each other and can precisely co-ordinate to create the nessesary gaps at just the right moment.

CGP Grey did a really nice, concise video on the topic of traffic and he addresses your point in the first 30 seconds. Coordination, not cars, is the problem.

https://www.youtube.com/watch?v=iHzzSao6ypE

This isn't what they studied, but a simple thought experiment shows a limited use case where traffic absolutely can be helped by speeding things up.

Let's imagine a world where self driving cars are required for freeway driving; this allows them to respond in a predictable and timely manor with respect to directives to avoid lanes (and not jump the line) as well as to go at an exact speed.

An event (accident, whatever) obstructs One of Five possible lanes for use (including the HOV lane) on a section normally rated at 60 MPH.

This reduces the capacity of the road by 1/5th, or alternately, one lane of flow should be re-distributed across 4 lanes (1/4th per lane).

Idealized solution: A temporary bypass zone is communicated to the self-driving cars. There is a lead up zone where the speed is expected to ramp up to the new target, followed by a merge zone where the lanes reduce and the flow is re-shaped to balance traffic evenly. The cars would then pass the incident zone in this higher speed lane-compressed flow, before expanding out and then slowing back down to normal speed.

Due to the unexpected nature of the incident there has also been a buildup of volume before the incident, so to alleviate that slightly higher flow will be allowed to drain the high pressure area.

In the above hypothetical case, for 4 out of 5 lanes nornally at 60MPH, I would prefer to imagine: (1 + 1/4) * 60MPH => 75, but round up another 5 MPH for the bypass flow for a total of 80MPH in the corrected flow area.

Many sections of freeway could likely support that safely ; they're often engineered very well but have conservative speed limits set for political and driver quality reasons. However some sections would 'cap out' at a lower actually safe speed; in those sections the above procedure could help minimize the traffic flow impact.

However... CGP Grey really nailed the real problem: https://www.youtube.com/watch?v=iHzzSao6ypE

⬐ robocat

Also introduce effective information to commuters to reduce flow: many drivers can vary their timing (come into work 2 hours later), or path (delivery schedule; go to a different office), or just cancel (go shopping tomorrow instead).

⬐ None

None

⬐ dev_dull

> Idealized solution: A temporary bypass zone is communicated to the self-driving cars.

There’s so many great opportunities like this once the cars are self driving and connected. For example, a ten lane highway without dividers! 8v2 split depending on the time of day and traffic patterns. How many times have you been stuck in a lane with the other lanes in the other direction completely open?

⬐ fuzz4lyfe

You could open up lanes a quarter mile at a time even depending on traffic demands.

Eg. Between exit 1 and exit 2, 8 northbound lanes are open. Between 2 and 3 we have 6 northbound lanes.

It's would be pretty disconcerting to travel in your self driving car and head full speed into oncoming traffic only to shift lanes a few moments before collision though.

⬐ dsfyu404ed

They had this in Montreal back in the day (i.e. the 1960s, when the risk of a head on crash was one you just accepted by driving).

There would be a bunch of lanes undivided from each other and over the lanes would be lights telling you which lanes were open for your direction of travel.

Movable barriers work too but are far more expensive.

⬐ dev_dull

Seattle has this with a physically separated highway. It’s closed in one direction and switches directions around noon.

Fun to wait at the entrance with a motorcycle. As soon as it’s open you have 5 miles where it’s physically impossible for another car to merge on.

⬐ kiliantics

Yes, nothing sounds more utopian to me than a world covered in 10-lane highways...

⬐ dev_dull

Hate to break it to you but the world is already covered in 10 lane highways.

⬐ hanniabu

I'm sure we'll start seeing autonomous driving only lanes in a few years.

⬐ nostrademons

Also, drafting. With human drivers it's not feasible to have cars travel 6 inches behind each other, because human reaction time is shitty enough that everybody would crash. With computer control you could easily have cars match speeds, then slowly get closer until they latch together and form a train. This'd both dramatically increase the carrying capacity of roads (with the default 1-car-length-per-10mph-of-speed rule, 7/8 of a highway is empty space), and it would improve fuel economy by reducing cross-sectional area and wind resistance.

⬐ sushisource

This is still a terrible idea. What happens when the car in front of you has an axel failure?

Oops, my car's instant reaction time is worth nothing because the brakes cannot physically prevent my imminent death.

⬐ Dylan16807

High quality brakes on all four wheels should be able to stop a car faster than an axle failure.

⬐ nostrademons

It seems like this is the exact same problem that was solved (to our satisfaction, at least) by trains over a century ago. If you're riding on the light rail and the train car ahead of you has an axle failure, what happens? We don't think very much about this case, because in practice it basically never happens.

⬐ sushisource

It works because they're physically connected already, which would be really really difficult with cars (standardizing the connectors, etc etc). Agreeing on a standard protocol for communication is a hard enough problem to start with.

⬐ nostrademons

Nobody who's looked at the economics of self-driving cars realistically thinks private ownership is an option: if you're putting that much capital investment in a vehicle that could operate 12-16 hours/day, your amortized costs go up by a factor of 6-8 if it's only operating for 2 hours/day. If we get self-driving cars it'll be in the form of ridesharing or rental services.

Agreeing on a standard protocol for both connectors and communications is a relatively easy problem if you have an industry with a dozen or so operators rather than 300 million private owners. It also solves the other major reason trains don't regularly crash, which is regular maintenance.

⬐ bluGill

Then nobody intelligent has looked at the idea. There isn't much gain from car sharing: more then half of the cars in the fleet will be used for one trip in the morning and one in the afternoon - rush hour is much busier than any other time of the day. Even if a car could be used for a second trip, it needs to get to the next rider, which means travel back out to the suburbs empty - adding wear and tear to the car and burning fuel (CO2)

Some people will car share, but most will decide that the convince of having their gold clubs in the trunk is worth having their own for the little cost difference it will be.

⬐ thereisnospork

Nonsense, if self driving is a $30k option on a camry, that makes it a 60k car to amortize. How many $60k+ BMWs sold last year?

⬐ mrpopo

Probably a small fraction of the total sales, given that the average new car price was about 3 times less (and many people buy second-hand cars). Therefore, private self-driving cars will only be available to a very small fraction of the population, and the rest of the population will have to use car-sharing.

⬐ xyzzyz

Nobody who's looked at the economics of self-driving cars realistically thinks private ownership is an option: if you're putting that much capital investment in a vehicle that could operate 12-16 hours/day, your amortized costs go up by a factor of 6-8 if it's only operating for 2 hours/day. If we get self-driving cars it'll be in the form of ridesharing or rental services.

This same reasoning applies to non-self driving cars, but somehow we do have a few privately owned cars around. The only way self-driving would make it any different would be if self-driving cars were so much more expensive that only very few would be able to afford it. If you however try to estimate the shape of the demand curve, you'll note that even today that are plenty of cars sold at $100k mark, so unless self-driving cars are many hundreds of thousands of dollars each, you'll still see privately owned self-driving cars.

More importantly, once the technology is out in the wild, many manufacturers will copy it, and it will push down the markup for self-driving capability rather low. You can sell a self-driving Toyota Corolla for $100k if you're the only manufacturer of self-driving cars. Once Nissan and Ford have their own equivalent technology, you can no longer do that.

⬐ Gibbon1

When I think of the economics of self driving cars I pull out of my keister a sub $10k price for that option and then estimate the monthly amortization cost at 'under $200/mo'

At that point I start worrying that self driving cars externalize the cost of congestion off the driver to the public at large. Everyone has to deal with congestion except the people inside their self driving cars yapping on their phones.

⬐ tremon

...which can be mitigated with a different high-tech solution: accurate sensors. If some critical component is near imminent failure, the car shouldn't allow itself to be included in a high-velocity train.

But I fear we have a trust problem there: we wouldn't trust the industry to be accurate in their sensor assessments, since the prevailing assumption (I'm looking at you, HP) is that these sensors are used to maximize revenue instead reliability.

⬐ danbolt

We have a similar thing going on here in Vancouver. The computer controlling the cars centrally manages their location and velocity, as to ensure that there's a breadth of passenger coverage around the metropolitan area. It's also elevated to help streamline trip times too.

People always talk about driving with gaps[1], but I've yet to see a simulator show how detrimental/beneficial these strategies are to individual drivers.

It feels like a hawks and doves style ESS (evolutionary stable strategy) problem. It appears to me that the strategy that eliminates the overall negative affect for the group (avoid creating phantom stop signs, by gapping or "always in the middle" strategies) is necessarily unstable.

The benefit to any single driver who does not follow that rule becomes increasingly high as more and more others do follow the rule. Even to the point of ignoring a beeping car I should think. I certainly feel the negative effect driving behind someone who creates a gap as more and more cars merge in front of them. In the pathological case the driver who insists on a safe interval between cars will make no progress at all.

1: (CGP Grey) https://youtu.be/iHzzSao6ypE

⬐ Noumenon72

You say you've observed it, but it doesn't make any sense. If you go 5mph slower than the speed of traffic, you will continuously open up a gap. You never need to slow down farther than that. The cars merging into the gap wouldn't be merging if your lane wasn't faster than their lane, so there's no reason you would have to slow down even farther. What you perceive as repeated slowing down will only happen if you sped back up to match the speed of the car in front of you after opening the gap.

⬐ hedora

Because you insist on the gap, your lane is 5mph slower than the other lane (because people pull in front of you after passing). Assume the other lane is doing 50 (65 mph speed limit, but there is congestion).

That lowers the throughput (number of cars that complete a trip in your lane) by ~ 10%. Also, the faster lane is now probably moving closer to your speed behind you than the 50mph you observe (because you are causing cars going 45mph to cut off cars going 50mph that lane).

The arrival rate of cars won’t change because you chose to go slow. So, if the road can handle 10,000 cars per unit time with normal congestion, it can now handle ~ 9000. That means per unit time, there are 1000 new cars sitting in the stop and go backlog that you single handedly created by creating the gap.

This has been shown time and time by traffic simulations. It only takes a small handful of slow drivers to create massive backups.

Also, the number of traffic fatalities is proportional to the difference in speed between the fastest and slowest car, so, statistically speaking, by being the slowest car, you are murdering people.

⬐ Noumenon72

The reason I am going 5mph slower in this thought experiment is because a continuous stream of cars is merging in front of me from the other lanes. (What the OP called the 'pathological case'.) They are the reason the lane is slower, and because they are not in the other lanes, those lanes will be 10% faster.

With the pathological case being so benign, the real life experience is even better. You might get a car moving in front of you once a minute, and usually a few seconds of slower accelerating or coasting is all you need.

To me the thing that really slows down traffic is people not moving left to let onramps merge. I think that's because they are afraid of missing their exit because no one is leaving gaps.

⬐ joshuak

I don't think you've considered what you are saying. You're not describing a gapping strategy, you're just describing a slower driver (i.e. slower traffic). There is no question that a car consistently driving slower than ambient traffic speed is a net drag on overall throughput. In any single lain of traffic all cars are bound by the slowest car. If you drive 5 mph slower than the car in front of you then the car behind you must drive 5 mph slower still to continually produce gaps behind you. As the video illustrates introducing a slower driver is one of the things that creates phantom stop signs.

Of course you must maintain speed. The point of a gap is to allow for adjustments without the hard breaking that would create a phantom stop sign. That is the overall intent of the system. Move the most people as expediently as is safe from point a to point b. The best way to do this is to avoid speed differentials, being slower then ambient traffic speed creates a speed differential.

⬐ Noumenon72

That's not true about the second driver behind me, because people are not pulling into his gap, because his lane is going 5 mph slower than the other lanes. So he establishes it once and is fine.

This is more of a thought experiment to show that you never have to keep slowing down to zero even if for some reason people continually enter your gap. I barely observe people entering my gap at all in practice, because all lanes are generally going the same speed so there's no benefit to it.

This reminds me of this great video: https://www.youtube.com/watch?v=iHzzSao6ypE

[CGP Grey did a video on this](https://www.youtube.com/watch?v=iHzzSao6ypE). Your goal, as a driver, should be to try to maintain equivalent distance between your car and cars in front of you and behind you.

⬐ Sohcahtoa82

reddit link syntax doesn't work on HN, btw.

⬐ yreg

Nevermind, raw markdown is good enough for this forum.

Stop/go is bad. Gliding is better for the collective and for your fuel efficiency.

CGP Grey has a great video on traffic flow: https://www.youtube.com/watch?v=iHzzSao6ypE

I am on the same page with everyone here about the problems with car-centered infrastructure, but I think perhaps we haven’t fully internalized the extent to which driverless, electric, shared vehicles will change this equation. It’s an entirely new paradigm - and even more so if cheap tunneling can be achieved. While Musk’s initial ideas about how to reduce the cost may be wrong, at least he’s trying to! His initial ideas about electric cars and rockets weren’t completely right either, because he was not an expert in those areas. He hired the most talented people in those fields and learned and changed over a period of years until he found what worked. It’s a good algorithm, and it helps to be wealthy so that you can survive the failures and dead-ends without running out of money.

There are two arguments in the article: that Musk is going about solving the problem in the wrong way, and that he is solving the wrong problem altogether by trying to put cars in tunnels. The author may well be right about the first, but I think he/she is wrong about the second.

Let’s think about everything that changes in a fully driverless, electric, shared, and tunnel-augmented vehicle ecosystem.

No more greenhouse gas emissions directly from vehicles (and none at all once the grid is fully renewable).

No more need to dedicate huge amounts of valuable land in our cities and suburbs to parking (cars can drive themselves to outlying areas to park or, better yet, can be shared).

Dramatically higher throughput because the human mistakes that cause congestion can be avoided (I recommend CGP Grey’s video on the causes of traffic: https://youtu.be/iHzzSao6ypE ). Driverless cars could drive faster and closer together, especially if they can communicate with one another.

Even more dramatic reduction in deaths and injuries as human error is removed from the equation.

Far fewer cars are needed in a shared-vehicle ecosystem. Most privately-owned cars are idle nearly all of the time, but they still take up space. Sharing vehicles allows us to reduce the amount of infrastructure needed for cars.

The average size of vehicles in the fleet can also be reduced. Right now people drive unnecessarily large vehicles because they might need the space a few times per year (annual family skiing trip, etc). These vehicles use up more energy and take up more space. In a shared-vehicle ecosystem, most of the vehicles can be something like a Smart ForTwo, with a smaller number of large vehicles that can be used by whoever actually needs them at any moment.

A shared-vehicle ecosystem could also include something like a cross between a scaled-up UberPOOL and a scaled-down bus: a Sprinter van (or equivalent) could pick up and drop off a dozen or so commuters who live in area A and work in area B. This improves the density of the system.

With affordable tunneling, freeways can go underground instead of destroying communities on the surface. This is one of the greatest evils of our car-centric infrastructure today, but with affordable tunneling we can abolish it.

Train-based mass transit will always be desirable for high-traffic corridors because it can be made far more dense. And despite this article’s attempts to paint him otherwise, Musk agrees with this - he is in talks to build a Hyperloop between Washington and Baltimore, as well as a lower-speed mass transit “loop” in Chicago.

However, trains will never be all that we need for transit, because they just can’t go everywhere. You will almost always need last-mile transportation at the endpoints, and there will always be routes that are not efficiently served by the train network. That’s where cars (or whatever we call the things they evolve into) come in.

A driverless, electric, shared, and tunnel-augmented vehicle ecosystem is probably the perfect mass transit system.

⬐ eesmith

"the extent to which driverless, electric, shared vehicles will change this equation"

Yes, I think it's agreed that such a system could/will change things dramatically. Let's assume that it is possible. The questions then are 1) when will the transition take place, and 2) how do we improve the current system until it happens?

If it takes 50 years, then it's rather pointless to wait before making big changes, or even to plan for such a transition. (By comparison, the US interstate system is only 60 some-odd years old.)

It's quite clearly not next year.

Nor would it be easy for cities like Miami and Amsterdam to go underground, if tunnels are what's needed to make such a transportation system work.

"A driverless, electric, shared, and tunnel-augmented vehicle ecosystem is probably the perfect mass transit system."

You may be missing a qualifier - perhaps "personal"? - in your description. The word "vehicle" includes buses, trams, and trains, so this summary includes many current subway and tram systems, except without a driver.

P.S. It's hard to predict if something really will cause a big change. I remember in the 1990s when Dean Kamen talked about the Segway as being the next transportation paradigm, "John Doerr speculated that it would be more important than the Internet" and "Steve Jobs was quoted as saying that it was "as big a deal as the PC"" (quotes from Wikipedia). When it came out, it turned out not to be a big change. I think e-bikes - an update of 1800s technology - have had a bigger impact than Segway.

⬐ jcranmer

> No more need to dedicate huge amounts of valuable land in our cities and suburbs to parking (cars can drive themselves to outlying areas to park or, better yet, can be shared).

Let's solve our congestion problems by doubling the amount of traffic on the roads! Sharing vehicles is a red herring; the peak traffic is caused by what's effectively a unidirectional, time-compressed mode of transit--once the car drops someone off at work, there's not enough trips nearby that it can do.

> Driverless cars could drive faster and closer together, especially if they can communicate with one another.

Yeah, except for all those unpredictable pedestrians walking on the street in busy cities. You could drive faster and closer together only if a) every car were so wired, and no one drove manually and b) it's a limited-access highway with little conflicting movement. It might help I-70 in Kansas; it's not helping any street in NYC.

> A driverless, electric, shared, and tunnel-augmented vehicle ecosystem is probably the perfect mass transit system.

No, it ain't. The way you get mass transit is you start packing people into tighter spaces. A single-occupant car, no matter how many times it's reused, no matter how tightly you pack them, is just way too much extra space. The twin Hudson river NEC tubes carry more capacity than the GWB, Lincon Tunnel, Holland Tunnel, Brooklyn-Battery Tunnel, and Brooklyn Bridge combined.

CGP Grey did an animation of it here: https://youtu.be/iHzzSao6ypE?t=3m46s

⬐ skrause

That video is just full of false assumptions. For example at 0:25 he attributes the delays between cars starting at traffic lights to bad reaction times of humans.

No, you start with a short delay because otherwise there is no way to reestablish the safety distance to the car in front of you. Which you still want to have with automated driving because self-driving cars won't solve sudden mechanical failures.

⬐ the8472

How do you think that safety distance is derived?

EV cars do not solve congestion

Autopilot cars can do a lot for congestion. If every driver implemented the "stay halfway between" algorithm mentioned in CGP Grey's "The Simple Solution to Traffic" video, there would be far less congestion.

https://www.youtube.com/watch?v=iHzzSao6ypE

EVs would also enable simpler tunnel construction and better tunnel economics. This is a part of Elon Musk's new proposals.

what is the validation strategy to show where driverless cars can quantifiably improve?

One big way in which automated drivers could improve traffic: By not being a jackass. I remember at one point driving down Westheimer, which is four lanes wide and one of the major thoroughfares of Houston, when I had to slow down for someone making a right turn to merge into traffic into a middle lane while their head was buried deep into the passenger side footwell looking through their stuff.

Then, there are the people who feel like they have to tailgate you within 6 feet during rush hour traffic on the highway. Also, the people who won't let you in for some personal justice you can't possibly understand.

It would only take a smallish fraction of cars implementing the "stay between" algorithm that CGP Grey mentions in his video to significantly improve traffic.

https://www.youtube.com/watch?v=iHzzSao6ypE

I've implemented this algorithm manually. (Much easier to do since I have the instant accelerator response of an electric car.) It does seem to improve traffic flow. Also, jackass tailgaters are sometimes confused by this, and decide to pass.

The more human drivers that are replaced by software, the less congestion there will be on the roads. It's delays in human reaction times which cause cars to back up on roads and take forever to get through intersections.

https://www.youtube.com/watch?v=iHzzSao6ypE

⬐ pmyjavec

I still don't see how the cars are going to entirely solve the problem of everyone needing to be in the same place at the same time, they still have to cope with each others presence, unless they can fly.

In my opinion a good public transport system does. I've spent time in Tokyo, the rail network is second to none, it's congested sure, but it works.

The problem is that people still need to get in and out of the cars for example, which means there is still wait time. Breakdowns will happen. All humans drivers will have to be banned etc.

It sounds to me like the auto-industry is still pushing a selfish agenda and the valley is buying it, because it's an opportunity to take more money.

For me, I'm happy because I'll still ride my bike and it will be a much safer place for me to exist because self-driving cars won't try and kill me, hopefully :)

⬐ mastermojo

I'm curious as to how a chain of cars would react to a gap appearing. The ideal balance would be to space the cars out evenly, but would that work on the individual car level when each driver looks at the cars in front and behind?