[saosebastiao]

I've never understood why people think traffic will move faster with self driving cars. The status quo is drivers driving well beyond the physical capabilities to stop given the conditions at hand. Sure, they might be able to cut down on reaction time, but they still can't do anything about physics.

Given that these vehicles will shift the risk model from driver to manufacturer, and subsequently programmed to obey the laws (which include right of way), we might actually see pedestrians and cyclists using their right of way instead of being bullied away from it.

The idea that cars can communicate with each other so they could drive closer together and faster is complete bullshit...Sure, it's possible, but what profit-driven company would ever take that risk knowing the real-world reliability of wireless communication?

The idea that they won't drive around looking for parking? Welcome to your traffic jam of the future: https://twitter.com/yann_rouen/status/807781862022246401

Pretty much all the evidence points to very slow traffic in the future of self driving cars. As someone who mostly walks everywhere, I'm pretty excited.

[kabes]

A lot of traffic jams are so called shockwave/phantom traffic jams and a lot of other ones are where lanes have to merge in each other. Those could be avoided with self driving cars. Maybe in the beginning they will be too cautious for that, but after some time and experience, I'm sure these optimizations will be implemented.

It may not make the traffic in downtown SF faster, but it sure will make the traffic on the 101 from SF to San Jose faster. And good luck walking that.

[dragonwriter]

> A lot of traffic jams are so called shockwave/phantom traffic jams and a lot of other ones are where lanes have to merge in each other.

And, to build on this point, a lot of urban ones are produced or exacerbated by improper behavior at stoplights.

[erispoe]

It is true but as pointed the benefits are mainly on highways.

[saosebastiao]

Those won't go away. They might be mitigated, but once again, you can only mitigate the portion that is due to driver error, and the major problem in those scenarios is physics.

The shock wave phenomenon is one caused by physics (it literally is modeled by fluid dynamics simulation), exacerbated by limited visibility, and exacerbated once again by human reaction times. You can only get rid of the human reaction times, and maybe a little bit of visibility due to communication (although I'm extremely skeptical that there is any incentive for cars to rely on wireless communication to make decisions).

Lanes merging is a physical bottleneck. Sure, humans might make the merge worse, but speed is still limited by the capacity bottleneck, not the friction of the merge. The zipper merge has never proven to be faster, merely safer and more space efficient. You'll get to the bottleneck faster, and cars that try to exit before the bottleneck will get out of your way faster, but that's about it.

[jedberg]

Those traffic waves are in large part psychology though. If every car traveled at the average speed you wouldn't have them. If even just 10% are self driving and have data on average speed for that section of road, they can not only avoid the wave but break them up, making traffic better for everyone.

I've even done this myself. I see a standing wave in front of me and slow to what I know is about average for that time of time. People cut in front of me as the gap gets bigger, but by the time I get to the choke point the wave dissolves as I pass through, and everyone behind me who was pissed about my slow speed is suddenly happy.

[saosebastiao]

I'm not convinced, and I don't think there is very much evidence either way. Are the traffic waves caused by erratic driving due to driver error at misjudging average speed? Or is it more caused by small fluctuations due to actual and unavoidable conditions? Would a self driving car see a plastic bag blowing in the wind and slam on its brakes, or drive right through it? What about a kitten? What about a bowling ball, or an unsecured 2x4 falling off a truck? Any one of those situations can cause a shock wave.

We know, due to fluid dynamics simulation, that reduced reaction times will make traffic more resilient to small fluctuations in speed (they can "recover" from the shock wave with lower space requirements), but when the freeway is at capacity there is no recovery room and the shock wave will happen regardless of reaction time.

[bashinator]

I try to leave 10-20 car lengths between myself and the next vehicle in this kind of stop-and-go heavy traffic. No waves for me! The anti-traffic essays indicate that doing what I'm doing will actually speed up the breakup of a traffic jam.

[galdosdi]

That's true, but depending on the local driving culture, this may just lead to many vehicles cutting in front of you and making the gap vanish. In metro NY/NJ, at stop-and-go speeds on freeways, 1 to 2 car lengths seems to be about as much as you can safely leave without it quickly being snatched away. Too bad.

[crucini]

This is an interesting insight. What if we replace 20 sequential cars with a huge "road train" ala Australia - a tractor with multiple trailers?

The road train has no cushion (ignore the few inches in pintle hooks) so it brakes as a unit. And accelerates as a unit. Does that make it's recovery from shocks 20x as good as 20 cars?

[jedberg]

The idea of traffic reduction is twofold. First is the fact that there can be a lot more carpools because you don't need the owner of the car to be inconvenienced to make the carpool work, so there will be an overall reduction of cars on the road.

Second, and more importantly, when you have only autonomous vehicles on the road, you can make assumptions that all drivers are perfectly rational, and then your safety margins can be smaller, allowing closer travel at higher speeds.

I suspect in the future, much like how when we transitioned from horse drawn carriage to motor vehicle, at first they will share roads, but then there will be autonomous only roads where the speeds will be higher.

[crucini]

> Second, and more importantly, when you have only autonomous vehicles on the road, you can make assumptions that all drivers are perfectly rational, and then your safety margins can be smaller, allowing closer travel at higher speeds.

Are you saying that a rational driver will never apply maximum braking?

[jmcdiesel]

There are non-rational things like animals, kids, and adults with their face in their phones to watch for, so it will never be fully rational...

However, the fact that the computer in the following car can detect instantly that the front car is slowing, it can react instantaneously and (theoretically, with similar braking distances) the following car would stop exactly the same distance (give or take a few inches) from the leading vehicle as when they were driving at speed...

[crucini]

OK, so we agree that the lead auto-car may still apply maximum braking unexpectedly. Therefore the follower needs to leave enough space to compensate for reaction latency, difference in braking power, etc.

So how does data communication (or lack thereof) affect this?

The follower can instantly detect that the leader is slowing via sonar/lidar/radar, right?

[jmcdiesel]

Seems like it would be near instantaneous, right? As soon as the leader brakes, the brake lights would be on (speed of light essentially) ... the following car would recognize that, along with radar/lidar type technology. I would imagine the reaction time would be nearly instant...

Then the distance between the cars that they should hold should be calculable by enforcing braking performance on the automated cars...

Assuming its enough, a simple 2 carlength rule would 1) give enough distance to stop and 2) allow for merging easily (second car would slot into place, following cars would slow slightly to make the gap again) ...

[jedberg]

Maximum breaking is still a possibility but you can do things like assume you won't get cut off and you can safely ride someone's blind spot and assume they will see you. Things like that.

[Florin_Andrei]

> I've never understood why people think traffic will move faster with self driving cars.

Because there's a huge difference between individual agents trying to maximize their own benefit to the detriment of everyone else (while also operating based on limited, local sensor data, and with limited processing power and slow reaction times), and a fully integrated traffic flow where fast, powerful agents communicate with each other, share sensor data and telemetry, and are able to make global optimizations.

Scenario #1 often produces pathologic outcomes that are way below global optimum. Scenario #2 can optimize traffic to the extent that human drivers would be unable to keep up with it (think rush hour traffic moving at legal speed limit nearly bumper to bumper with no accidents).

[trvlngwlbry]

The video you linked to was interesting - thanks for sharing - but I didn't follow how that's related at all to self-driving cars driving around looking for parking. The video seems like more an example of what happens when individual households all own cars and don't carpool when taking their kids to school.

If the kids being dropped off at that school started using self-driving Uber Pools, then that video would be better described as "Welcome to your traffic jam of the past."

[saosebastiao]

The relation is that instead of driving around looking for parking, they queue up at their new bottleneck: loading and unloading. Nobody in the video needed to park, and yet traffic within that area was still moving slower than 3-4mph. Place this phenomenon on city streets where they won't have space for conveniently designed queuing areas, and cars will stop in the road, blocking anybody who is trying to move by. Downtown traffic during rush hour will be moving at a snails pace.

I'm open to the idea that carpooling might increase, but where will it come from? If it is coming from public transit, that would be a net increase in congestion. If it is coming from cars, it would be a net win...but self-driving cars should make ubers cheaper, not more expensive, and the relationship with supply/demand at lower cost would suggest that people would move away from uber pools and towards uberx. I would imagine that the more flexible ride-matching of uber pool (compared to traditional carpooling) would make it easier to use uberpool than it currently is to carpool, and with the right incentives (congestion charges that are waived for carpooling?), we could probably make it work pretty well. I don't know though, the complexity of the dynamics here makes it pretty hard for me to predict with any confidence.

[galdosdi]

This! Self-driving cars makes car use much cheaper, and I can't imagine any other outcome but substantially more car use as a result, leading to more traffic. At some point we have to deal with this in some way, such as tolling, especially in denser urban areas, where land values are expensive, and the hassle/time cost of driving/parking are the only things metering motorists' use of this valuable resource.

[crucini]

> Sure, it's possible, but what profit-driven company would ever take that risk knowing the real-world reliability of wireless communication?

I think it can be done; the following car may have to brake hard if communication is lost with the leading car.

Let z1 be the safe following distance behind a non-smart car, and z2 be the safe following distance behind a smart car. z2 < z1.

Follower approaches leader and settles at z1. Follower attempts to contact leader. If contact is successfull, follower measures link quality and computes z3=f(z1, z2, quality). If link quality is perfect, z3 can be z1 - in which case the slightest link disturbance causes hard braking.

If link quality is 50%, z3 might be avg(z1, z2), and the follower has more time budget to avoid braking during tiny dropouts.

[casylum]

I think traffic will get worse with self driving cars. If you don't need to be in the car, it can run errands for you during the day. Remember how computers were supposed to lead to a paperless office?

[anigbrowl]

I don't really agree, though as someone who also walks everywhere I'd be glad if you were right. My guess is that as self-driving cars take off to the point of being generally accepted rather than a curiosity, there'll be less and less incentive to operate a car of your own - much as you can still in theory get around by horse but it's so much hassle to own one that hardly anyone bothers to do so.

[serge2k]

> The status quo is drivers driving well beyond the physical capabilities to stop given the conditions at hand.

because that's not the most efficient way to move traffic. Yes, a road at it's limit is going to be worse off. Perfect merging and other better habits will help in a lot of places. Just think of all the times you see some idiot merge in at 50 way before the end of the lane.