If you normally drive with TACC set to five, and your wife drives with two, it sounds as though your preference is to leave more space, which means that without Autopilot engaged you would probably have had enough space to have prevented this accident, but that your wife would not have. On the other hand, perhaps she drives with TACC set to two because she feels she has a quicker reaction time. Maybe AP settings should be stored with the driver's profile, so that it more closely matches the style of the driver.
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Somebody else reported a similar accident HERE. The following distance was again set to 2. Setting 2 is not a fixed distance. As you speed up, the distance increases but it looks like it doesn't increase far enough. They could adjust that but then people are just going to use setting 1. It looks like, speed based auto adjustment should be increased so much that the distance at 70 mph with the new setting 1 should be greater than the current setting 2. Until then, don't use 1 or 2.
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Blastphemy
Member
bushburner
Member
Looks to me like you drive too close to the car in front of you.
But how close were you following and how quickly did the car in front of you stop? It is possible to drive in such a way as the "accident" can't be avoided. (i.e. the 100% braking capability can't stop the car in time.)
davidc18
Active Member
Glad you are both okay. I've had both of ours set to early and 7 which is what I would recommend to everyone. Maximize the safety system.
Glad everyone was okay. My X recently smacked a deer and I had AP set at 74 MPH, following distance of 4, AEB set to early, and it still didn't see the deer. Although, I knew it never would see animals.
I had a very similar incident: heavy traffic, AP engaged, ~15 MPH, one hand on the wheel, but I wasn't paying attention. The alert system did it's job, chimed and braked hard. I braked as well but my reaction was way too late! I got out to check how close I was to the car in front of me and there was just over a foot between our bumpers.
I had a very similar incident: heavy traffic, AP engaged, ~15 MPH, one hand on the wheel, but I wasn't paying attention. The alert system did it's job, chimed and braked hard. I braked as well but my reaction was way too late! I got out to check how close I was to the car in front of me and there was just over a foot between our bumpers.
I drive on 1 or 2 and have had close encounters but not because I'm driving that close but because the cars in front of me almost collided and were in an emergency braking situation. Every time the Tesla stopped enough or I stomped on the brakes hard enough to keep from hitting the cars. (Only because I trust myself more than I trust Autopilot beta.) In all instances the cars behind me had it rough and almost collided with me. When you drive on 1 or 2, with less following distance, your car is more aggressive and will "gas"/brake more often and at a much higher rate.
Likely the reason you still hit the cars was because they crashed which caused a very abrupt reduction of speed to zero. If it was you driving you'd likely have slammed into them at a much higher rate.
Also, consider tire and road conditions. Slip even the slightest bit on gavel, or your tires are worn down enough or night the right amount of pressure, or added weight in the car, or the road composition, etc... Any of those factors and many others can play into the fact that you kissed the car in front of you.
One other thing to consider, you may have thought you stomped the brakes, but I doubt you really stomped them as much as you could have. One thing I learned from being on race tracks and going through performance schools is that you really don't know what it's like to stomp a brake pedal to the ground until you try it a whole bunch of times. It's many feet less distance, something you really should experience on a skidpad.
Likely the reason you still hit the cars was because they crashed which caused a very abrupt reduction of speed to zero. If it was you driving you'd likely have slammed into them at a much higher rate.
Also, consider tire and road conditions. Slip even the slightest bit on gavel, or your tires are worn down enough or night the right amount of pressure, or added weight in the car, or the road composition, etc... Any of those factors and many others can play into the fact that you kissed the car in front of you.
One other thing to consider, you may have thought you stomped the brakes, but I doubt you really stomped them as much as you could have. One thing I learned from being on race tracks and going through performance schools is that you really don't know what it's like to stomp a brake pedal to the ground until you try it a whole bunch of times. It's many feet less distance, something you really should experience on a skidpad.
Blastphemy
Member
This seems to be a common misconception that the numbers adjusted by the cruise control lever refer to a finite distance. The numbers are variable measurements corresponding to a time-based distance that represents how long it takes for Model X, from its current location, to reach the location of the rear bumper of the vehicle ahead. (That's a quote from the manual.) Ergo, driving with a setting of '1' at 70mph results in a much greater following distance than when driving at 15mph. The '1' setting is supposed to be the absolute minimum safe following distance, not that you're following the car in front of you with 1 foot or 1 car length in between.
Exactly.
Sorry to hear about the collision. Glad that no one was hurt. That's the most important thing.
There are a few issues:
1) Did the car respond within an appropriate time window?
2) When the car sounded warning and braked, did it apply full braking force right away or ramp up gradually?
3) Was the collision physically avoidable or inevitable given the circumstances?
Answering these may require data analysis by Tesla. I'm not going to attempt to answer them, but to bring up a few points of discussion. From OP's description, it seems that the car responded appropriately, but didn't brake fully right away. Had it applied full force, could the collision have been prevented?
Tesla's automatic braking already applies more braking power than comparable systems in Mercedes (Distronic Plus) that I've driven ('14 ML, '13 S550, '09 CL). The '14 MB system applies up to 40% of the maximum braking force and beeps to signal that additional braking power is needed. The brakes are primed for full braking so that as soon as the driver responds to the beep and touches the brake pedal, the brakes are clamped with 100% force.
I much prefer the Tesla system because it requires less driver intervention. However, I can see the reasoning behind MB's design decision -- it's because the car isn't always right. If the car senses an impending collision from a ghost reading, an inaccurate shadow of a car, braking 100% right away could end up causing a lot of rear-end collisions. As an example, last year a Kia K900 braked urgently on an empty stretch of highway by itself during Car & Driver testing. Or, if I am speeding up toward a slow car with the intention of turning at the last second, automatic braking would be annoying and potentially dangerous (this has happened to me in both MB and Tesla, with MB simply beeping and Tesla applying a moderate amount of braking that was overcome by additional accelerator input).
Before these cars can interpret situations correctly 99.99% of the time, these will remain difficult design compromises.
One thing is for certain - Model X's braking is an area that needs improvement. The brake pedal feedback is spongy upon hard braking, and the braking distance is longer than expected for a car with this type of (exceptional) straight line performance. I don't know if the brakes were upgraded from P90D to P100D, but given the increased weight and power, the brakes should be sized up to match. The few times I've braked hard, I wish my P100D stopped in a shorter distance. Model S is better. If the Model X stopped as well as the typical Porsche, OP's collision may well have been prevented.
There are a few issues:
1) Did the car respond within an appropriate time window?
2) When the car sounded warning and braked, did it apply full braking force right away or ramp up gradually?
3) Was the collision physically avoidable or inevitable given the circumstances?
Answering these may require data analysis by Tesla. I'm not going to attempt to answer them, but to bring up a few points of discussion. From OP's description, it seems that the car responded appropriately, but didn't brake fully right away. Had it applied full force, could the collision have been prevented?
Tesla's automatic braking already applies more braking power than comparable systems in Mercedes (Distronic Plus) that I've driven ('14 ML, '13 S550, '09 CL). The '14 MB system applies up to 40% of the maximum braking force and beeps to signal that additional braking power is needed. The brakes are primed for full braking so that as soon as the driver responds to the beep and touches the brake pedal, the brakes are clamped with 100% force.
I much prefer the Tesla system because it requires less driver intervention. However, I can see the reasoning behind MB's design decision -- it's because the car isn't always right. If the car senses an impending collision from a ghost reading, an inaccurate shadow of a car, braking 100% right away could end up causing a lot of rear-end collisions. As an example, last year a Kia K900 braked urgently on an empty stretch of highway by itself during Car & Driver testing. Or, if I am speeding up toward a slow car with the intention of turning at the last second, automatic braking would be annoying and potentially dangerous (this has happened to me in both MB and Tesla, with MB simply beeping and Tesla applying a moderate amount of braking that was overcome by additional accelerator input).
Before these cars can interpret situations correctly 99.99% of the time, these will remain difficult design compromises.
One thing is for certain - Model X's braking is an area that needs improvement. The brake pedal feedback is spongy upon hard braking, and the braking distance is longer than expected for a car with this type of (exceptional) straight line performance. I don't know if the brakes were upgraded from P90D to P100D, but given the increased weight and power, the brakes should be sized up to match. The few times I've braked hard, I wish my P100D stopped in a shorter distance. Model S is better. If the Model X stopped as well as the typical Porsche, OP's collision may well have been prevented.
EVie'sDad
Member
I think that was one of the first settings I adjusted on day one, changing from a 2 or 4 to at least a setting of 5, anything less is insufficient distance for the car to react to unexpected braking at highway speeds. Haven't had any incident in the past 15 months with that setting even when traffic slows unexpectedly ahead of my Model S.
X Fan
Active Member
Agreed....I'm fortunate to not drive in congested areas such as Cal/NY, etc. but when traveling on Interstates I have always set to 7. When traveling around Naples' streets, and at lower speeds, I'll reset to 4 or 5.
I've only used 2 in DC when stuck in bumper to bumper traffic.
btw: glad OP and his family is safe.....
One thing that came out of the NHTSA report is they described the TACC feature "BCW" (Brake Capacity Warning). If TACC senses that its max allowed braking force cannot slow down your car in time, it will sound a FCW. But this isn't your regular FCW which only sounds when you're just about to hit something (like within a second or two), this is warning you that the car knows TACC won't brake hard enough.
Bottom line: If you get a FCW alarm while using TACC/AP, you should take over and initiate braking ASAP. Even if it doesn't look like your car is about to crash. By the time the situation unfolds and becomes obvious, it may be too late to avoid the accident.
Bottom line: If you get a FCW alarm while using TACC/AP, you should take over and initiate braking ASAP. Even if it doesn't look like your car is about to crash. By the time the situation unfolds and becomes obvious, it may be too late to avoid the accident.
Jrogville
Member
MP3mike take a look at the Design Studio. Right there under safety features is says "collision avoidance". I would think that's pretty clear.
Jrogville
Member
Do you understand that the person hitting from behind is at fault? Would Tesla set up a system where it will put the blame for the accident on you? If you avoid hitting someone in front of you and someone else rear-ends you because they did not respond in time or were following too closely, the fault for he accident is the person behind you, no matter what the circumstance of you're stopping, even if your's was a needless stop.
Life's not just about who is at fault. Being not at fault won't un-decapitate you, or bring your backseat passengers back to life, or make months of insurance paperwork and repair wait time go away….
It's important to act in a manner that attempts to avoid collisions and injury, regardless of who would be at fault.
You're absolutely right. The wording there is misleading, especially given the description of the feature in the manual.
Hey, maybe it is like "TCAS" in an airplane where the "avoidance" means it sometimes yells at you in a robotic voice to move up or down.
