keydiver said:
GRA said:
Specifically in this case, if the Tesla hadn't been going 9 miles over the speed limit this accident never would have happened, because the semi would have cleared the road before the Tesla arrived.
You know this HOW? :? I haven't seen any evidence that suggests that 9 mph would have prevented this accident.
Basic math. The difference between 74 and 65 mph is 13.2 ft./sec. Photos of the trailer show that the Tesla impacted about in its middle, or centered around 26.5 feet from either end (53 ft. trailer). The Model S is just under 6.5 feet wide, so add 3.25 feet to the 26.5 feet needed to clear the rear end of the trailer, or 29.75 feet. [
Edit the preliminary NTSB report says the Tesla struck 23 feet forward from the rear end of the trailer. If that's the leftmost point of impact rather than the center, then the center of the Tesla would be almost exactly at the trailer midpoint. If it's the midpoint then the distance to clear would be 3.5 feet less.] If we assume that the truck was traveling at only 10 mph while crossing the road, that's 14.67 ft./sec. so it would have taken just over 2 seconds for it to completely clear the Model S' path. So, if the Tesla had been going 65 instead of 74 for at least the last two seconds prior to impact, the rear end of the trailer would have cleared its path. In this case a random act of timing. but nevertheless a fact. If the truck was going slower (unlikely, I'd say) then it might have been 3 or more seconds. At 15 mph that's 22 ft./sec., so under 1.5 seconds @ 65 would have sufficed. What we don't yet know is if the truck stopped before making the turn, or was moving the whole time.
[
Edit: Went back and read Baressi's account, and he says that he'd waited to let another car pass before making the turn, at which time the Model S was in the left lane, and it subsequently changed into the right lane. If accurate Brown must have initiated the lane change. What we don't know is how early that was done.]
keydiver said:
At this point, we have nothing but heresay as to how fast the semi was traveling, how much distance there was between the vehicles when the semi driver first saw the Tesla, and at what point he accelerated to try to clear the intersection. That being said, I do usually drive the speed limit when I'm on Autopilot. Do you also think every car should be disabled from having their Cruise Control set for anything above the speed limit? Its no different. Every car on the road can be driven in an illegal manner.
Of course, that goes without saying. It used to be the case that CC maximum speeds in this country were much more limited than they are now, but there's really no excuse for any CC to allow set speeds over 85 mph in this country, which is the highest legal limit for any public road (and that's only on a single toll freeway in Texas). For those cars which are equipped to know the speed limit, they shouldn't be able to set a cruise control speed above that limit - any such driving would require full manual control.
I'm the first to say that many of our speed limits are set well below the design speeds of the roads they're on, and while there's been some movement to adjust speed limits upwards (including the 7 states that now have 80 mph speed limits on rural Interstates) to reflect that, we've still got a long way to go to make speed limits more realistic. Maybe such a limit on CC would be the goad that caused more legislatures to do that. Since the entire interstate system was built to the same standards, there's no logical reason why some states only allow 65, some 70, some 75 and others 80, unless the specific circumstances of the road (traffic volume, curvature, grade etc.) require that. I-5 in Oregon up the Willamette Valley is limited to 65 (although the Oregon Legislature recently allowed 70 mph speed limits), but it's 70 mph for all California interstates, including I-5 in the Central Valley (outside of urban areas), which is equally straight and flat. At least in California, 75-80 is quite typical of how fast people actually drive on such freeways, and at or below the design speed of the road. I-15 in California has that same 70 mph limit, but it changes to 80 at the Nevada border for no logical reason. I-84 in Oregon is also 70 (up from 65 this past February), which changes to 80 at the Idaho border for equally arbitrary reasons.
keydiver said:
But, your constant harping on Autopilot is very annoying, as Autopilot is simply lane-keeping. The Autopilot was working perfectly, as the Tesla stayed in its lane. And, there have already been plenty of explanations as to perhaps why the AEB didn't kick in.
I find apologia for Tesla's autopilot/ACC/AEB design choices equally annoying, and more importantly, dangerous. Since ACC/AEB is an integral part of autonomous driving along with lane keeping, and I consider the systems as they currently exist unsafe
as Tesla allows them to be used, I have zero agreement with any post which seeks to absolve Tesla from responsibility over allowing the use of autopilot/ACC in situations in which
they themselves have said it's unsuitable, and will continue to provide counterpoint to such excuses. This is a matter of public safety, and I don't believe that Tesla has any right to test their self-driving systems and gather data using a public that has neither been informed of nor given their assent to such testing. So far, no member of the public has been injured or killed by such use, but it's only a matter of time. Fortunately for Tesla, in this case there was 300 feet of open field, a power pole and another 50 feet of open field for the car to plow through before coming to rest. Next time there may be innocent bystanders in the recovery zone. [
Edit: As it was, it missed the BP gas station at the intersection solely because the station was on the SW rather than SE corner - otherwise it would likely have hit a car, the pumps or the convenience store there.]
I agree with your calcs (did them myself last night assuming instantaneous decel as you did, and did the forehead smack then). Two seconds from impact traveling @ 74 mph, the Tesla is 108.53 (x 2) ft. away, or 217.06 feet. Assuming magic decel to 65 mph (95.33 ft./sec), in the next two seconds it will travel only 190.67 feet, leaving it 26.4 feet short of impact, so it will still hit the truck 26.4/95.33 x 14.67 = ~4.0 feet further aft, if I've got the right numbers in the right order this time. 
