NTSB To Investigate Fatal Accident in San Antonio Involving Ford BlueCruise

[Maxx]

Your particular citation doesn't mean a whole bunch without providing information, such as how much the average speed differed from the posted speed. There are also no error bars on the data on the graphs. If the average speed deviated little from the posted speech, the "data" you post would essentially show that it's safest to drive the posted speed. The first graph is data from 55 years ago, three generations previous to the current. Many of the drivers who provided that data are probably deceased or at least not driving very much today.

I give up. Let the record show natural selection has begun. If the subsequent generation of drivers looks more like Jim, stick to speed limit, and if they look like Maxx, drive to survive, just like me:

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[Jim Lewis]

For one thing, @Maxx, apart from how average speed compares to the posted speed limit when the studies were done, the graphs you posted cite "average" speed. It might have been better to refer to median speed. Averages can be driven off the true center by outliers and skewness. If deviations from the median speed were mostly higher, that would make the average speed higher than the median speed, i.e., a few real speeders make the average go quite a bit higher, and the average speed won't truly reflect the speed the middle of the pack is traveling.

An average is like a seesaw. The further out a point is from the average, the more leverage it has in moving the average. The best averages are with normally distributed data, which I doubt highway speed data is.

EDIT: Have to correct myself. According to Microsoft Copilot, highway speed data is typically normally distributed: https://copilot.microsoft.com/sl/bydhQ7K2J2W

This normal distribution of speeds allows for straightforward statistical calculations and is useful for traffic engineers and planners in understanding and managing traffic flow1.

Learn more
1highways.dot.gov2safety.fhwa.dot.gov3numerade.com4ascelibrary.org

 

[Maxx]

For one thing, @Maxx, apart from how average speed compares to the posted speed limit when the studies were done, the graphs you posted cite "average" speed. It might have been better to refer to median speed. Averages can be driven off the true center by outliers and skewness. If deviations from the median speed were mostly higher, that would make the average speed higher than the median speed, i.e., a few real speeders make the average go quite a bit higher, and the average speed won't truly reflect the speed the middle of the pack is traveling.

An average is like a seesaw. The further out a point is from the average, the more leverage it has in moving the average. The best averages are with normally distributed data, which I doubt highway speed data is.

I really didn't Google much on this and don't plan to. People can do that on their own. I am getting too tired to try to prove a case. I do research when something is not obvious to me. It is just common sense to minimize the speed differential between me and the 4 vehicles around me and to place myself in part of the traffic that allows that at a comfortable speed for me and my passengers. If I can do that at a lower speed to maximize range and safety, I try to do that. If I can't, I go with the flow whatever that speed is, damn the signs (that never resulted in a speeding ticket). In all years of my driving this practice has never failed me. Now this is when I drive safe and sensible. I have had my stupid mad max moments too but this is not the time to incriminate myself.

If living by the sign works for you, regardless of what the traffic around you is doing, go for it.

 

[Jim Lewis]

@Maxx, to save you a Google search, see reference #2 from my previous post. A lot of what it has to say agrees with the gist of what you have been saying. It says a dominant factor in determining speed limits is that limits should be set within 5 mph of what the 85th percentile of traffic travels on a section of road: Speed Concepts: Informational Guide - Safety | Federal Highway Administration (dot.gov) So, theoretically, posted speed limits reflect, within 5 mph, what most drivers think is a safe speed, when this philosophy is applied in determining speed limits.

Table 3. Primary factors used to establish posted speeds

​	Percent​	time used
Factor​	By state agencies​	By local agencies
85th percentile speed​	100​	86​
Roadside development​	85​	77​
Accident experience​	79​	81​
10 mph pace​	67​	34​
Roadway geometrics​	67​	57​
Average test run speed​	40​	34​
Pedestrian volumes​	40​	50​

Source: Ref (17)​

 

[Newton]

I watched "herd mentality" put six cars over the cliff (including mine) on a nice fall day in the Cascades. The sign that everybody else ignored said it was a 35 mph corner, it didn't say that the curve was shaded and could be icy in the late fall. Unfortunately I had stopped to help and lost a nice car, fortunately I had exited about 30 seconds before it got hit and went over the edge.

Actually, I misspoke. I think only four of them went over the cliff. One bounced back on and was upside-down, and the car that pushed my (parked) car over the cliff stayed on the road.. By the way, the pickup lost control the fastest, way earlier than the other cars. The tow truck driver said that they were the worst.

If you have been 50 feet away from an auto crash at highway speeds, you would probably pay attention to the speed signs. Especially if you have spent an hour in a rural area waiting for an ambulance for the injured (no cell access), fortunately nobody died.

 

[reffahcs]

I think what Maxx is trying to say is that at a certain point if the delta between the speed of a single vehicle and the average traffic speed is too great then the slower vehicle is more of a danger than the vehicles driving 15, 20 etc... over the speed limit. I don't think Maxx is implying we follow the crowd like a bunch of blind lemmings.

I'm sure the few folks that live in Maryland (I forget their names, but I know we have a few) can attest to cases where people are driving 35-40 MPH in the middle lane on the beltway which is posted 55, but most people are driving 65-75. And I'm not going to debate speed limits, that's personal preference.

 

[Danface]

Maybe a bad driver would be helped by automation more than a good driver? Averages and medians are fine on a macro scale but personally, I've been careful and lucky enough to have never been in a bad accident and it's been years since being in a fendfer bender. Having said that, for me, there are no circumstances I would be working the pedals and turning the wheel

 

[Jhawks9028]

That's not a question at all actually. Recognizing an object that is not moving is difficult for radar. This is a very well known and understood limitation of radar. Every manufacturer knows it. The NTSB, DOT, IIHS, AND NHTSA all know of this. It's even written in many vehicle owners manuals. And it is why radar didn't prevent every similar accident involving Teslas.

It was dark and the stopped car has no lights on. Therefore the vision system also couldn't see it. An attentive driver with eyes open and paying attention may or may not have seen it.

This is like running a news media story wondering why rain is wet.

That’s not entirely true. Doppler radar relies on movement, but traditional radar does not. Think about ships and land. The land isn’t moving but radar picks it up in great detail. What matters is wavelength, refresh rate, processing speed, and what the software is supposed to do when it detects an object. A car sitting on a freeway makes for some fast closure speeds. This incident may have revealed a Blue Cruise filter meant to screen out false echos and noise that is too strict, over filtering a real object. It’s a tough balance since I don’t want emergency braking activated when I’m going 75 mph unless it’s legit. False alarms and violent stops will make me sell fast!

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