3 ms·

> it's always able to track the car in front of me perfectly I've always wondered how this would really work. What happens when the car ahead changes lanes or

by jobu 11y ago

> it's always able to track the car in front of me perfectly I've always wondered how this would really work. What happens when the car ahead changes lanes or exits the freeway? Have you run into any issues with weather (rain, snow) interfering with the sensor?

mikeash 11y ago
Typically the car is not following the car in front, merely regulating speed to avoid ramming it. In my car, at least, if the car in front changes lanes or exits, then the cruise control system speeds back up to whatever speed I set it to. This can make for some exciting speed differentials if, for example, everybody is moving 20MPH and they open up a big gap by changing lanes, and my set speed is 70MPH. But it doesn't accelerate aggressively, and this is a rare occasion anyhow.
rconti 11y ago
I'm not sure if I've used it in the rain yet, but my understanding is that, yes, the sensor needs to be kept clean. It follows the SPEED of the car in front of me; I still steer. I assume it uses steering wheel sensors to detect that it should be following the car slightly to the left of me when, say, I'm going around a left-hand curve. The lane keeping system uses a camera to detect lane markings. I'm not sure how it decides whether or not to follow exits, but I know from the Tesla autopilot descriptions that it's not perfect.
wibr 11y ago
That depends on the sensors which are used. Most current ACC systems use radar, which should not be affected by weather but has other problems like high cost, narrow field of view and you only get speed and distance as data points which are not always easy to interpret correctly. Ideally it's combined with a camera to get more information about the environment like land markings, so that you know if the car in front of you is actually in your lane or just going around the corner in the lane next to you. The camera is obviously prone to glare, raindrops, etc.. When the car ahead changes lanes or exits the freeway, the system will try to find another car as a target vehicle and adapt the speed accordingly to keep a certain timegap, if it can't find a target it will behave like normal cruise control.
- vonmoltke 11y ago
  A more sophisticated (but expensive) radar sensor could do the job without the camera. A sensor capable of Doppler processing, sweeping, and tied to some sort of platform telemetry (GPS, INS, etc.) could maintain a large and fairly comprehensive situational picture. Add moving target indication to the signal processing and it could form tracks on all other vehicles on the road, which would provide the motion vectors for them without the need for another sensor. You could even use track behavior to detect anomalies in the road, assuming you have multiple tracks. I could go on all day about this (having actually worked on MTI radar for several years), but I have actual work to do. :P

by jobu 11y ago

mikeash 11y ago

Typically the car is not following the car in front, merely regulating speed to avoid ramming it. In my car, at least, if the car in front changes lanes or exits, then the cruise control system speeds back up to whatever speed I set it to. This can make for some exciting speed differentials if, for example, everybody is moving 20MPH and they open up a big gap by changing lanes, and my set speed is 70MPH. But it doesn't accelerate aggressively, and this is a rare occasion anyhow.

rconti 11y ago

I'm not sure if I've used it in the rain yet, but my understanding is that, yes, the sensor needs to be kept clean. It follows the SPEED of the car in front of me; I still steer. I assume it uses steering wheel sensors to detect that it should be following the car slightly to the left of me when, say, I'm going around a left-hand curve. The lane keeping system uses a camera to detect lane markings. I'm not sure how it decides whether or not to follow exits, but I know from the Tesla autopilot descriptions that it's not perfect.

wibr 11y ago

That depends on the sensors which are used. Most current ACC systems use radar, which should not be affected by weather but has other problems like high cost, narrow field of view and you only get speed and distance as data points which are not always easy to interpret correctly. Ideally it's combined with a camera to get more information about the environment like land markings, so that you know if the car in front of you is actually in your lane or just going around the corner in the lane next to you. The camera is obviously prone to glare, raindrops, etc.. When the car ahead changes lanes or exits the freeway, the system will try to find another car as a target vehicle and adapt the speed accordingly to keep a certain timegap, if it can't find a target it will behave like normal cruise control.

vonmoltke 11y ago
A more sophisticated (but expensive) radar sensor could do the job without the camera. A sensor capable of Doppler processing, sweeping, and tied to some sort of platform telemetry (GPS, INS, etc.) could maintain a large and fairly comprehensive situational picture. Add moving target indication to the signal processing and it could form tracks on all other vehicles on the road, which would provide the motion vectors for them without the need for another sensor. You could even use track behavior to detect anomalies in the road, assuming you have multiple tracks. I could go on all day about this (having actually worked on MTI radar for several years), but I have actual work to do. :P