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2019 Pedestrian anti-collision systems in cars 7

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GregLocock

GregLocock

Automotive
Apr 10, 2001
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Rather a tale of woe.
One could argue that reducing pedestrian deaths by ~10% is good, but at the same time, if the systems were working properly that'd be 100% fewer. The graph on p25 says it all, about the simplest case at the lower speed. Two of the systems at least tried to do what you'd hope they would set out to do, the other two might as well have been switched off.



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Greg Locock


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Another source here says 2.3 seconds was an average. A major issue is that braking behind a car you are following is very different than braking for a pedestrian, since the latter is an unexpected occurrence, while one has some modicum of expectation of the car in front of us doing something that requires us to break. A random pop-up pedestrian has the added reaction time from the fact that your gaze might not even be anywhere near the pop-up pedestrian, which adds to your nominal reaction time.

Army studies for performing target detection tasks have resulted in something like 3.6 seconds for detecting a 90% probability of detection target in a sensor field of view with low to moderate clutter. Now, a camera-based sensor can potentially get a decent reduction in search time, but has more limitations with respect to lighting conditions; which is probably why the Tesla is not going to do wellin this type of test. A lidar-based sensing system is more likely to detect pop-up anomalies, but while the individual detections are close to instantaneous, the computer must process multiple frames to get the false alarm rate down to something usable, so likely something on the order of 1/3 second, resulting in something on the order of 16.7-ft stopping distance. So, while that'll reduce accidents, I suspect many accidents didn't even have that much warning distance.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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Alternatively, we could ditch our vehicles and ride bicycles.
The unfolding climate crisis does not allow for the luxury of powered transportation, and that includes EVs.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
 
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With the Internet being the way it is these days, one could repeatedly search on 'Any Topic You Like' and "x.x seconds", where x.x is repeated as a sequence of 'xx' ASCII characters to spell out "MARBLECAKE ALSO THE GAME".

 
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VEIBLL - see my last sentence. I bet at higher speeds you can't get the ABS to stop by standing hard on the pedal. It would make no sense for the ABS system to not work when stomping the pedal down very hard, the type of hard that will lock-up the brakes even on dry asphalt. That's the exact time it's supposed to kick in.
 
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Agree this is limited to low speeds, I had always assumed that must be the case.

I was specifically addressing the "just above....back below" aspect of your suggestion, which is effectively out-of-phase with what has actually happened.

The last sentence doesn't help, as the cause and effect timing observed is the opposite.

Having driven Mercedes for 20 years, I'm no longer surprised at the extent of their over-engineering. Two reverse gears, not joking. Wipers that will run backwards to park midway through an upstroke (implies H-Bridge motor controller). Another bit of ABS code for icy hills? ...easy.

 
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The cut-off speed for ABS used to be 10 kph on some cars. One reason for this is that car parks often have rather a loose surface and it is better to lock the wheels than roll along on gravel or mud or grass.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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The "average sized adult" in the study was 5' 11" and white. Is all auto testing still this biased against women and non-Caucasians? For reference, the CDC states the average US height is 5' 4" for women and 5' 9" for men.
crash_test_hoazcb.png
 
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If I might wander a bit: Why can't we hook these smart cars to something useful besides driving. I can see buying a cheap used smart vehicle, parking it in my driveway, hooking all the car sensors (OBD port?) to something like a light show machine and having a dance party driven light show.
Or with facial recognition, something could pop up and have that person removed.........
 
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"...light show..."

Tesla has threatened a Party Mode.
 
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Electric cars ("crowd sourced") could be used to stablize the grid (helps with renewables), and provide emergency power to one's home (during blackouts). Obviously such capabilities would have to have strict limits, so the owner could get to work the next day.

Recent research is pointing towards "Million Mile" batteries, so the concern about impact of battery life might be a reasonable tradeoff.

 
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Certainly, one could ensure that the processors would only participate while the car is being charged. If we assume that the processor in the car is comparable to my old laptop, which burns about 40 W, a Tesla battery would take 2 months to discharge with that kind of load, so in a 10-hr idle time while parked is equivalent to losing about 2.2 miles of driving range.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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Pretty sure there's more processing power in a Tesla then in a laptop, by a factor of many, many times. Which likely means the power usage is much higher too.
 
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There are solutions to reduce processor power consumption if the vehicle is parked and merely providing backup power. E.g. Tiny co-processors; and/or the usual mix of very low duty cycle, sleep mode, and interrupts.

It would be a requirement to minimize processor power consumption, but it's not a significant technical challenge.
 
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These systems can still be cost-effective even if 100% crash avoidance is an unattainable goal. Crash injury risk appears to increase with velocity squared, not velocity, so even a small reduction in impact speed should considerably reduce the severity of crash injuries.

AASHTO stopping sight distance for 20 mph is 115 feet. SSD uses 2.5 second perception/reaction time, which is intentionally conservative. 115-2.5*1.47 = 41.5 feet stopping distance.

Supposedly the Texas Transportation Institute had research subjects driving on a closed course for a "sign study." At points around the course, they had people hiding behind bushes throw a mannequins out on the roadway in front of the test subjects. The first time, average reaction time was about 1.5 seconds. The average reaction time for subsequent mannequin tosses was closer to 1/2 second. So, reaction time for an expected event is much lower than for an unexpected event.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -
 
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The Camry demonstrates that the systems could work as advertised, at 20 mph. Quite why 2 companies think its OK to release systems that have negligible effect, or none at all, is the issue.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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bacon4life (Electrical),
You'll get no sympathy from me. As far as I can see, the world has been designed and built by short people for the benefit of short people.
Trust me, the only advantage of being tall is psychological.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
 
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the only advantage of being tall is psychological.
Click to expand...

Depending on the exact height, probably; it's certainly be demonstrated in studies that taller, white, males have sociopolitical advantages in business and job choice.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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