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One of the next obvious steps for self-driving vehicles is “flocking” or drafting; this is an almost trivial problem once two or more vehicles are autonomously

One of the next obvious steps for self-driving vehicles is “flocking” or drafting; this is an almost trivial problem once two or more vehicles are autonomously locked within a few inches of each other.

jstanley 6y ago
If you have a car only a few inches behind you and you spot a problem and need to emergency brake, you can't actually start braking until the car behind has started braking, otherwise the car behind will crash into the back of you. If you have 3 cars in a row, and the first car spots a problem, it can't start braking until after the 2nd car has started, but the 2nd car can't start braking until after the 3rd car has started. It gets linearly more dangerous as more cars are added. Not saying it can't be done, but the problem is more subtle than just working out how to stop the cars from crashing into each other at speed: they also need to be able to brake in emergencies without crashing into each other. Possibly the way to do it would be to mechanically couple the cars like a train, so that it is safe for the one in front to start braking earlier than the one behind, albeit with reduced performance.
- cheerlessbog 6y ago
  The idea is predicated on autonomous control and presumably the vehicles communicate in real time...they all brake together at the delta V of the least capable member.
  - jstanley 6y ago
    The "real time" control loop between the sensor on one car and the brakes on the same car is much tighter than that between the sensor on this car and the brakes on another car and then feedback from the other car that braking has started. I don't actually know how long it takes between the computer deciding to brake and the car actually starting to slow down, but I expect you can't just throw out a message saying "I'm braking immediately" and start braking without any kind of confirmation that the message was received, and expect it to be OK. But maybe you can afford to wait for a confirmation? The speed of light is pretty fast, and you're not transmitting that many bytes. Especially if you consider that a human could easily take 200 milliseconds to react to something even if it's really paying attention. You could request a braking confirmation from the other side of the Atlantic and still come out ahead!
    - adav 6y ago
      There could be some leeway to initiative braking on following cars quicker with control loop similar to existing emergency brake assist systems [1]. These currently apply the brakes quicker and more powerfully than a driver’s foot when the car thinks it’s in an emergency situation. The same signal could be sent to following cars by the time the driver sufficiently engages the pedal. [1] https://en.wikipedia.org/wiki/Emergency_brake_assist https://en.wikipedia.org/wiki/Emergency_brake_assist
  - nradov 6y ago
    Braking delta V depends on many variables such as mechanical condition, component temperature, road surface friction, etc and is thus difficult to predict to that level of precision. Even with real-time communications, if the vehicle in front slows less than expected due to hitting a pothole or something then the vehicles behind are going to have to react damn fast to avoid a collision. It might be achievable on certain roads but it will be a tremendous engineering challenge. Don't expect to see this in passenger vehicles any time soon.
    - NickM 6y ago
      Yeah all good points, and just to add, there's also the challenge of maintaining perfectly reliable and low-latency communications over any sort of wireless medium in a variety of unpredictable outdoor conditions.
deleted 6y ago
[deleted]
infecto 6y ago
Once we solve autonomous driving. Decades out.
kevin_thibedeau 6y ago
> two or more vehicles are autonomously locked within a few inches of each other. Never going to happen so long as potholes and poorly patched roads exist.
ashtonkem 6y ago
Just build high speed rail. It’s available today, rather than in some hypothetical future once autonomous cars work.
Tade0 6y ago
Too close for comfort I think. Brakes are still hydraulic and they react when they react - with a different delay for each vehicle.
grecy 6y ago
Tesla have talked extensively about "Convoy Mode" for the upcoming Semi Truck where they will do exactly that. Maybe the gap will be more than inches, but the idea is they draft together. I think the plan for early autonomous driving is the first one in the line will have a human driver, and the others will follow autonomously in convoy.
scottlocklin 6y ago
Or you could just ride on a much less complicated, safer and more efficient railroad.

jstanley 6y ago

If you have a car only a few inches behind you and you spot a problem and need to emergency brake, you can't actually start braking until the car behind has started braking, otherwise the car behind will crash into the back of you. If you have 3 cars in a row, and the first car spots a problem, it can't start braking until after the 2nd car has started, but the 2nd car can't start braking until after the 3rd car has started. It gets linearly more dangerous as more cars are added. Not saying it can't be done, but the problem is more subtle than just working out how to stop the cars from crashing into each other at speed: they also need to be able to brake in emergencies without crashing into each other. Possibly the way to do it would be to mechanically couple the cars like a train, so that it is safe for the one in front to start braking earlier than the one behind, albeit with reduced performance.

cheerlessbog 6y ago
The idea is predicated on autonomous control and presumably the vehicles communicate in real time...they all brake together at the delta V of the least capable member.
- jstanley 6y ago
  The "real time" control loop between the sensor on one car and the brakes on the same car is much tighter than that between the sensor on this car and the brakes on another car and then feedback from the other car that braking has started. I don't actually know how long it takes between the computer deciding to brake and the car actually starting to slow down, but I expect you can't just throw out a message saying "I'm braking immediately" and start braking without any kind of confirmation that the message was received, and expect it to be OK. But maybe you can afford to wait for a confirmation? The speed of light is pretty fast, and you're not transmitting that many bytes. Especially if you consider that a human could easily take 200 milliseconds to react to something even if it's really paying attention. You could request a braking confirmation from the other side of the Atlantic and still come out ahead!
  - adav 6y ago
    There could be some leeway to initiative braking on following cars quicker with control loop similar to existing emergency brake assist systems [1]. These currently apply the brakes quicker and more powerfully than a driver’s foot when the car thinks it’s in an emergency situation. The same signal could be sent to following cars by the time the driver sufficiently engages the pedal. [1] https://en.wikipedia.org/wiki/Emergency_brake_assist https://en.wikipedia.org/wiki/Emergency_brake_assist
- nradov 6y ago
  Braking delta V depends on many variables such as mechanical condition, component temperature, road surface friction, etc and is thus difficult to predict to that level of precision. Even with real-time communications, if the vehicle in front slows less than expected due to hitting a pothole or something then the vehicles behind are going to have to react damn fast to avoid a collision. It might be achievable on certain roads but it will be a tremendous engineering challenge. Don't expect to see this in passenger vehicles any time soon.
  - NickM 6y ago
    Yeah all good points, and just to add, there's also the challenge of maintaining perfectly reliable and low-latency communications over any sort of wireless medium in a variety of unpredictable outdoor conditions.

deleted 6y ago

[deleted]

infecto 6y ago

Once we solve autonomous driving. Decades out.

kevin_thibedeau 6y ago

> two or more vehicles are autonomously locked within a few inches of each other. Never going to happen so long as potholes and poorly patched roads exist.

ashtonkem 6y ago

Just build high speed rail. It’s available today, rather than in some hypothetical future once autonomous cars work.

Tade0 6y ago

Too close for comfort I think. Brakes are still hydraulic and they react when they react - with a different delay for each vehicle.

grecy 6y ago

Tesla have talked extensively about "Convoy Mode" for the upcoming Semi Truck where they will do exactly that. Maybe the gap will be more than inches, but the idea is they draft together. I think the plan for early autonomous driving is the first one in the line will have a human driver, and the others will follow autonomously in convoy.

scottlocklin 6y ago

Or you could just ride on a much less complicated, safer and more efficient railroad.