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2019 Pedestrian anti-collision systems in cars
7

2019 Pedestrian anti-collision systems in cars

2019 Pedestrian anti-collision systems in cars

(OP)
Rather a tale of woe. https://www.aaa.com/AAA/common/aar/files/Research-...

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.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 2019 Pedestrian anti-collision systems in cars

Fundamentally, the problem is intractable; the car stopping distance at 20 mph is on the order of 63 ft, with a stopping time on the order 2.8 seconds, but in 2.8 seconds, a pedestrian going 3 mph will have already crossed the entire width of the traffic lane, barring them actually stopping in the middle. Any closer, the car won't stop in time.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: 2019 Pedestrian anti-collision systems in cars

"100%"

That'll require high-powered X-rays, to detect pedestrians that are about to dart out from behind something opaque to all other sensor technologies. winky smile

Point being, existing electronic sensors (cameras, radar, lidar) are not omniscient. In the autonomous vehicle debates, too many are making precisely this false assumption that the systems are somehow omniscient.

To help clarify thoughts, if we allow the proposal that such systems can someday soon be 100% perfect, then it follows that speed limits can be eliminated. Which would be fun.

Area for improvement: As a human driver, I'm able to look under most parked vehicles watching for moving feet. In 2019, as far as I know, no electronic system includes this technique.

"...stopping distance at 20 mph is on the order of 63 ft..."

That must * include a generous dollop of human reaction time, so arguably not entirely applicable to automated systems.

* Since stopping distance is generally considered to be proportional to speed squared, if 20 mph is 63 feet, then 60 mph would be 567 feet (excessive). Thus the 63 feet must include generous reaction time.

RE: 2019 Pedestrian anti-collision systems in cars

IRstuff,

If the car is doing 20mph (32kph) and it decelerates at 0.8g, it takes 1.1s and covers 5.1m (17ft). This does not account for the driver's reaction time.

--
JHG

RE: 2019 Pedestrian anti-collision systems in cars

You have to include the 2 seconds it takes before the driver looks up from their phone.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 2019 Pedestrian anti-collision systems in cars

There was ~2 seconds of reaction and application time included in the total stopping distance. A fully automatic system could shave over a second off that number, which would save about 39 ft.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: 2019 Pedestrian anti-collision systems in cars

Quote (Wiki)


Average Dry Stopping Distance (Assuming two-thirds of a second reaction time)
Speed 20 mph
Thinking Distance 20 feet
Braking Distance 20 feet
Total Stopping Distance 40 feet

Quote (Greg)

I suppose there are customer acceptance reasons why you wouldn't do a full ABS stop, whatever the morality of that is.
I don't quite understand you here.
Admittedly my vehicles are older but we get a lot of snow and ice on the roads here.
In icy conditions an ABS stop in my vehicles takes about three times the distance of a normal stop without ABS.
Admittedly the ABS prevents a skid when the wheels lock up and it gives a second chance to back off the brakes and brake properly.
Triggering ABS and keeping it engaged won't get me stopped before the stop sign and the cross traffic.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 2019 Pedestrian anti-collision systems in cars

63 feet may be accurate.
3 feet reaction time.
3 x 20 feet with ABS.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 2019 Pedestrian anti-collision systems in cars

"...~2 seconds of reaction and application time..."

Of course it varies, but 2s is not typical.

You should remember the technique for counting off seconds: "A thousand and one, a thousand and two..."

Typical reaction time (within the normal distribution) is usually quoted as 0.8s. It's perfectly fair to round that to one second.

Two seconds is widely recommended as a 'Safe Following Distance' (measured in seconds) for good conditions. Obviously it wouldn't be very safe if it was the same as the typical reaction time.

---

All that said, perhaps two seconds is the average, with most drivers normally distributed around 0.8s, but the distracted or sleeping outliers wildly distorting the average. But that's not actually meaningful.

Outliers could distort the average for automatic systems. Just leave the clock running when they have a failure, and stop the clock (days later) after they've come back with a SW fix that passes. Average might end up as 3 hours. Not meaningful.

Point being, never embed outliers in averages without commentary.

---

In any case, human reaction time is not applicable to automated systems.


RE: 2019 Pedestrian anti-collision systems in cars

"In icy conditions an ABS..."

I live in the forest on a gravel road that regularly becomes a sheet of ice in winter. Studded tires and 4Matic AWD are helpful.

Creeping down the icy hill, when the smooth ice is covered with fluffy snow (that can pack or 'raft' under the studded tires), is a bit scary.

In these conditions (presumably slow speed), I've noticed that my car (Mercedes) allows me to override the ABS function.

When the fluffy snow rafts under the studded tires, preventing the studs from biting into the ice, the ABS function is unhelpful. Each ABS pulse refreshes the raft of snow.

But I discovered that if I press the brake pedal slightly harder, the ABS function stops. This allows me to lock-up the wheels, which almost instantly grinds off the rafts of snow, and allows the tire studs to bite into the ice.

This response is repeatable, so I presume that this is yet another hidden and otherwise unmentioned feature.

I have no inkling of the permitted speed range of this override.

RE: 2019 Pedestrian anti-collision systems in cars

When I took my first drivers test many years ago reaction time was tested. 0.55 seconds was the pass mark.
That was physical reaction time. You knew the light was going to go red and were waiting to slam your foot on the pedal.
Add some time to realize that you are facing a threat before the physical reaction starts.
ABS is better than locking the brakes and going for the ride.
Much better is backing off the brakes and re-applying a little less brake so that the ABS does not engage.
After years of driving icy roads before ABS was a feature I seldom engage ABS.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 2019 Pedestrian anti-collision systems in cars

Recommended safe following distance was 3 seconds, the last I heard anyone talk about it.

The cited article quotes a nominal 1 to 2 seconds from the stimulus to actually getting the foot onto the brake pedal and another 0.5 seconds from then to actually getting the brake engaged. This is consistent with the stopping distance calculations I've seen elsewhere. Note that physiological reaction time is on the order of 0.25 seconds, from stimulus to response, but that's in a test situation where the subjects are expecting something that they have to react to. When that imperative is removed, or substantially delayed, the reaction time increases. Moreover, most reaction time tests using hand-held buttons, which is different than removing one's foot from one pedal and placing it on another.

https://nacto.org/docs/usdg/vehicle_stopping_dista...
https://law.lis.virginia.gov/vacode/46.2-880/
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_r...

A driver, using left-footed braking, could probably shave 0.75 seconds off that.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: 2019 Pedestrian anti-collision systems in cars

Google: Two-Second Rule

Then Google: Three-Second Rule

If your Google looks like mine, the latter leads to basketball.

Acknowledged that some areas recommend a three-second rule instead of a two-second rule to give an additional buffer.

Let's just agree that YMMV.

In any case, human reaction time is not applicable to automated systems.

RE: 2019 Pedestrian anti-collision systems in cars

There's more to reaction time than mere "hear the bell and feel the dribble"

I won't easily forget a line from an Air Incident Report that crossed my desk some decades ago (the instrument panel had flopped down onto the pilot's lap at Rotate): "Following a delay measured in milliseconds during which I fought to suspend my disbelief...."

A.

RE: 2019 Pedestrian anti-collision systems in cars

VEIBLL - There is no ABS over-ride. The ABS probably has a low speed threshold so you are likely travelling just above that threshold and the heavy braking brings you back below where it shuts off. Also, the ABS won't know the car is still moving if all 4 wheels are stopped.

RE: 2019 Pedestrian anti-collision systems in cars

Creeping down an icy hill covered with fluffy snow all happens between 0 to 5 kmh.

The ABS would still chatter away, assisting with steering away from the edge, but allowing the speed to escalate.

When the speeds gets too high, pushing the brake pedal more firmly would reliably lock-up the wheels, scrubbing off speed at the cost of no steering.

The technique is to modulate between these two, for the minute it takes to get down the hill.

Opportunities to experience this are thankfully rare, but I've used this technique several times.

Vehicle is 2008 Mercedes E350 4Matic Sport (W211 chassis).

Excuse the thread drift.

RE: 2019 Pedestrian anti-collision systems in cars

I think that the reaction time in these estimates is very conservative. It's not uncommon for me to bump things from a cupboard and catch it before it hits the countertop. At less than a one meter drop, I'm recognizing what is happening, reacting, moving my hand about the same distance as my foot would have to go to get to the brake pedal, and catching the cup or whatever in less than half a second. A lot of that is muscle memory and bypasses the brain. But that applies to driving as well.

See also:
https://www.exploratorium.edu/hockey/saves2.html
https://www.nbclearn.com/science-of-nhl-hockey/cue...

RE: 2019 Pedestrian anti-collision systems in cars

I have found that backing off the brakes and then applying as much brake as I dare without enough to trigger the ABS is more effective.
If you can try it safely in a few months please share your results. I will be trying the ABS on snow and Ice this winter with my wife's 2018 car. Please don't tell her of my intentions. grin
Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 2019 Pedestrian anti-collision systems in cars

Another source here https://copradar.com/redlight/factors/index.html 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! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: 2019 Pedestrian anti-collision systems in cars

btw, Table 1 from http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_r... by the Transportation Research Board shows that AASHTO uses 2.5 seconds for their perception-reaction time.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: 2019 Pedestrian anti-collision systems in cars

2
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."

RE: 2019 Pedestrian anti-collision systems in cars

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".

RE: 2019 Pedestrian anti-collision systems in cars

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.

RE: 2019 Pedestrian anti-collision systems in cars

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.

RE: 2019 Pedestrian anti-collision systems in cars

(OP)
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: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 2019 Pedestrian anti-collision systems in cars

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.

RE: 2019 Pedestrian anti-collision systems in cars

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.........

RE: 2019 Pedestrian anti-collision systems in cars

"...light show..."

Tesla has threatened a Party Mode.

RE: 2019 Pedestrian anti-collision systems in cars

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.

RE: 2019 Pedestrian anti-collision systems in cars

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! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: 2019 Pedestrian anti-collision systems in cars

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.

RE: 2019 Pedestrian anti-collision systems in cars

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.

RE: 2019 Pedestrian anti-collision systems in cars

2
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. - http://xkcd.com/319/

RE: 2019 Pedestrian anti-collision systems in cars

(OP)
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: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 2019 Pedestrian anti-collision systems in cars

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."

RE: 2019 Pedestrian anti-collision systems in cars

Quote:

the only advantage of being tall is psychological.

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! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: 2019 Pedestrian anti-collision systems in cars

Tell that to the NBA and the NFL.

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