Emergency Brake Assist -safety feature or serious hazard?

Emergency Brake Assist -safety feature or serious hazard?

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Discussion

monoloco

Original Poster:

289 posts

191 months

Friday 11th September 2015
quotequote all
Emergency brake assist –safety feature or serious hazard? ( with an 'R' in BRAKE this time!)

(NB although the vehicle referred to in this post is a Mercedes, I’m sure other marques have similar systems –hence posting it in General Gassing

So there we were fighting our way round the usual Friday afternoon car park on the M25. Stop-start traffic and we’d just peaked at maybe 50mph when a couple of cars ahead someone dabbed his brakes. Usual scenario, the car in front of me then braked a little harder and even though I don’t tail-gate, I had to step on my own brakes a little bit harder still –nothing heavy but still a reasonable degree of deceleration intending to scrub off maybe 20mph.

Ordinarily nothing untoward except I’m driving a nice shiny new Mercedes ML350 (my weekday workhorse) and it’s fitted with the latest M-B collision avoidance and ‘Emergency Brake Assist’ systems as standard spec. This uses sensors in the front of the car to detect a possible impact and sound a warning bleeper. However, if you then touch the brakes while the warning system is activated it assumes it is a genuine emergency and applies the ‘Emergency Brake Assist’. In other words it suddenly overrides your own braking and slams the brakes on to their absolute maximum.
What started as a modest bit of braking resulted in the car’s electronics taking over and suddenly trying to do a full on emergency stop –ABS pulsing and tyres smoking in the outside lane of a packed motorway. The whole thing took maybe one or two seconds before the car ahead stopped braking and the sensors decided we were no longer on collision course (which we never were anyway). At this point the systems relaxed and gave me back control just before we came to a full halt. I fully expected the guy behind to slam into the back of us (odds-on he sh*t himself though!) and no idea if the resulting ‘coil-spring’ effect of the braking resulted in any rear-end shunts further back in the queue. The experience was terrifying and I seriously question whether these systems are genuine safety feature –or completely the opposite!


Edited by monoloco on Friday 11th September 14:30

TurboHatchback

4,151 posts

152 months

Friday 11th September 2015
quotequote all
I would suggest the driving not the system was the problem here, your description suggests your definition of tailgating is very different to mine. If you're needing to brake heavily close behind another car on a motorway then your observations were poor and/or you were dangerously close to begin with.


Also the title typo is rather leaving the floor open for awful puns.

justanotherJC

383 posts

151 months

Friday 11th September 2015
quotequote all
monoloco said:
... even though I don’t tail-gate
The EBA system seems to have a different opinion. smile

I would have thought that MB have calibrated the system to act fairly normally in most situations, but in this case it decided you were still approaching the car in front too rapidly and took action.


eldar

21,614 posts

195 months

Friday 11th September 2015
quotequote all
TurboHatchback said:
Also the title typo is rather leaving the floor open for awful puns.
I'm not going to rise to it.

justanotherJC

383 posts

151 months

Friday 11th September 2015
quotequote all
TurboHatchback said:
Also the title typo is rather leaving the oven door open for awful buns.
FTFY.

SHutchinson

2,040 posts

183 months

Friday 11th September 2015
quotequote all
You were lucky to not roll it you pudding!

chris watton

22,477 posts

259 months

Friday 11th September 2015
quotequote all
eldar said:
TurboHatchback said:
Also the title typo is rather leaving the floor open for awful puns.
I'm not going to rise to it.
hehe

anonymous-user

53 months

Friday 11th September 2015
quotequote all
Don't panic OP, the Team have been notified and will be immediately helicoptered in to assist in any way possible:


Thermobaric

725 posts

119 months

Friday 11th September 2015
quotequote all
Sounds like things went a little a-rye...

I'll see myself out.

anonymous-user

53 months

Friday 11th September 2015
quotequote all
Indeed, and the OP can count himself lucky he didn't become the jam filling in an accidental 3 car sponge or he would have been waiting for a Battenberg cop car to arrive!

LordHaveMurci

12,034 posts

168 months

monoloco

Original Poster:

289 posts

191 months

Friday 11th September 2015
quotequote all
apologies for the unfortunate typo in the title! Someone better phone the local plod to send a jam-sandwich to arrest me!
Anyway, I would point out that I was categorically NOT tail-gating. I was a sensible distance back from the car in front, it then braked unexpectedly and fairly sharply. I'd have had to be half a mile back not to have needed to brake to some extent myself. I braked moderately -not more than about 20-25% of full capacity and would have easily stopped comfortably and with a significant safety margin. Trouble is the M-B system doesn't seem to differentiate between that and full on emergency. It simply seems to think if the vehicle is closing on the one in front it will impact the obstacle, regardless of the fact the driver is already controlling the brakes and is going to stop in plenty of time. I can only assume that the system builds in a massive safety margin on the braking distance required -ie it takes a 'worst case' on how slippery the road is and just slams everything on despite the fact we were on a warm, bone dry road.

Meanwhile the link from LordHaveMurci is interesting and indeed along the same lines -shame I hadn't spotted it before I posted the original.

Thermobaric

725 posts

119 months

Friday 11th September 2015
quotequote all
Surely if the front sensor was able to ping the car in front, you were too close?

monoloco

Original Poster:

289 posts

191 months

Friday 11th September 2015
quotequote all
Common sense (which admittedly seems to be absent from many drivers on the M25) says you leave a gap big enough to see, react and stop in. That's exactly what I'd done -supported by the fact the car is also fitted with an anti-tailgate system that flashes a different warning light if you get too close to the vehicle in front at steady speed (ie not closing on it). That light was not illuminated before this incident took place. However, as the car in front braked, obviously the distance between me and it closed slightly before I reacted and started to brake myself so presumably at this point the sensors picked up the other car. To avoid this happening you'd need to leave double the safety gap -ie enough room to see, react, brake AND the same distance again for the sensors to think you'd got enough room to do that all over again. At no time did the gap narrow to a point where it was looking like an accident was going to happen -I started braking moderately and had plenty of room to stop even at the moderate level of brake pressure I was applying. The system just totally over-reacted and instead of preventing an accident it very nearly caused one. Its easy for anyone who hasn't experienced this to say its all my fault for being too close but I categorically wasn't -the system may be a good idea in theory but its just too crude -all or nothing. In my view the algorithm is flawed and turns what could be a clever safety feature into a significant hazard. Doing an unnecessary emergency stop in the outside lane of the M25 would get you a ticket for dangerous driving -so how come the car can do it for you?

anonymous-user

53 months

Friday 11th September 2015
quotequote all
monoloco said:
Common sense (which admittedly seems to be absent from many drivers on the M25) says you leave a gap big enough to see, react and stop in. That's exactly what I'd done -supported by the fact the car is also fitted with an anti-tailgate system that flashes a different warning light if you get too close to the vehicle in front at steady speed (ie not closing on it). That light was not illuminated before this incident took place. However, as the car in front braked, obviously the distance between me and it closed slightly before I reacted and started to brake myself so presumably at this point the sensors picked up the other car. To avoid this happening you'd need to leave double the safety gap -ie enough room to see, react, brake AND the same distance again for the sensors to think you'd got enough room to do that all over again. At no time did the gap narrow to a point where it was looking like an accident was going to happen -I started braking moderately and had plenty of room to stop even at the moderate level of brake pressure I was applying. The system just totally over-reacted and instead of preventing an accident it very nearly caused one. Its easy for anyone who hasn't experienced this to say its all my fault for being too close but I categorically wasn't -the system may be a good idea in theory but its just too crude -all or nothing. In my view the algorithm is flawed and turns what could be a clever safety feature into a significant hazard. Doing an unnecessary emergency stop in the outside lane of the M25 would get you a ticket for dangerous driving -so how come the car can do it for you?
The things is,modern cars are now so easy to drive, the vast majority of drivers don't make any effort to familarise themselves with a new (to them) vehicle. They just get in, stick it in "D" and zoom off. If the first time you have to use the brakes hard is a genuine emergency, then you have pretty much failed as a driver imo.

Day in, Day out, drivers are surprised by things their car does, and in an unfortunate few cases, that surprise leads to accidents, injury and even death. No one would pick up a hand gun and just mess around with it without any instruction, and yet that is exactly what happens with our cars........


lightthefuse

426 posts

171 months

Friday 11th September 2015
quotequote all
I'm just here for the OT puns/GBBO pics, and you've certainly risen to the occasion (fnarr fnarr)!

I'm with the safety feature peeps - City Safety in the V70 has helped me avoid a couple of shunts where I was a little too lax with the brake pedal. Also got in the way once (cue Kimi Raikkonen radio chatter), but on the whole I'm OK with it. In 25-odd thousand miles it kicked in three times, and two of those times was indeed my own stupidity, even if it was unlikely to have involved trading paint.

AER

1,142 posts

269 months

Saturday 12th September 2015
quotequote all
Max_Torque said:
monoloco said:
Common sense (which admittedly seems to be absent from many drivers on the M25) says you leave a gap big enough to see, react and stop in. That's exactly what I'd done -supported by the fact the car is also fitted with an anti-tailgate system that flashes a different warning light if you get too close to the vehicle in front at steady speed (ie not closing on it). That light was not illuminated before this incident took place. However, as the car in front braked, obviously the distance between me and it closed slightly before I reacted and started to brake myself so presumably at this point the sensors picked up the other car. To avoid this happening you'd need to leave double the safety gap -ie enough room to see, react, brake AND the same distance again for the sensors to think you'd got enough room to do that all over again. At no time did the gap narrow to a point where it was looking like an accident was going to happen -I started braking moderately and had plenty of room to stop even at the moderate level of brake pressure I was applying. The system just totally over-reacted and instead of preventing an accident it very nearly caused one. Its easy for anyone who hasn't experienced this to say its all my fault for being too close but I categorically wasn't -the system may be a good idea in theory but its just too crude -all or nothing. In my view the algorithm is flawed and turns what could be a clever safety feature into a significant hazard. Doing an unnecessary emergency stop in the outside lane of the M25 would get you a ticket for dangerous driving -so how come the car can do it for you?
The things is,modern cars are now so easy to drive, the vast majority of drivers don't make any effort to familarise themselves with a new (to them) vehicle. They just get in, stick it in "D" and zoom off. If the first time you have to use the brakes hard is a genuine emergency, then you have pretty much failed as a driver imo.

Day in, Day out, drivers are surprised by things their car does, and in an unfortunate few cases, that surprise leads to accidents, injury and even death. No one would pick up a hand gun and just mess around with it without any instruction, and yet that is exactly what happens with our cars........
The solution to this problem is to make them so easy to drive that they drive themselves!

GravelBen

15,654 posts

229 months

Saturday 12th September 2015
quotequote all
monoloco said:
Anyway, I would point out that I was categorically NOT tail-gating. I was a sensible distance back from the car in front, it then braked unexpectedly and fairly sharply. I'd have had to be half a mile back not to have needed to brake to some extent myself. I braked moderately -not more than about 20-25% of full capacity and would have easily stopped comfortably and with a significant safety margin. Trouble is the M-B system doesn't seem to differentiate between that and full on emergency. It simply seems to think if the vehicle is closing on the one in front it will impact the obstacle, regardless of the fact the driver is already controlling the brakes and is going to stop in plenty of time.
Was your initial brake application gradual or sharp (in speed of hitting the pedal, not overall force)?

IIRC some of the systems are set up to compensate for people who just don't push the pedal hard enough, and interpret a sudden/sharp lighter application as a weak attempt at emergency braking and kick in.

Whether thats the case with your car or not I have no idea though!

Chilli

17,318 posts

235 months

Saturday 12th September 2015
quotequote all
I've got this on my new car, and I hate it. It is bloody dangerous. I've had the brakes applied hard for getting too close to the car in front. e eruthing was in order....I was shifting lanes and needed to be closer than the system liked to carry-on. By applying the brakes as it did made the situation worse. (I live in Dubai where driving standards are appalling at best).

Another example....approaching a supermarket car-park there is a slight bend in the road. On this left-handler was parked a delivery van...absolutely no obstruction, just parked half on the kerb....I get to within 30 feet of so and the bloody brakes are slammed on again.

Will be asking the dealer to disconnect it when it goes in for its first service,

ging84

8,825 posts

145 months

Saturday 12th September 2015
quotequote all
GravelBen said:
Was your initial brake application gradual or sharp (in speed of hitting the pedal, not overall force)?

IIRC some of the systems are set up to compensate for people who just don't push the pedal hard enough, and interpret a sudden/sharp lighter application as a weak attempt at emergency braking and kick in.

Whether thats the case with your car or not I have no idea though!
This is emergency brake assit what the Op talks about it collision avoidance, Mercedes call it collision prevention assist plus.