4 ms·

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

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.

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.