Hacker News Reader

Comment by matte_black | Hacker News Reader

Wow, after all these years I finally learned the name of this phenomenon, constant bearing decreasing range.

I recall a scene in the movie Sin City where two cars crash and the camera was moving in CBDR to the perpendicular car as it zoomed into the impact site. I thought it was a cool shot.

Also I’ve almost hit pedestrians several times when they were obscured by my A pillar. Sometimes I wonder if I would have actually hit them if anyone would have believed I didn’t see them, now I know the proper term to describe the cause of such an accident.

View on HN

The Sidewinder missile is based on this phenomena. Early guided missiles attempted to home in directly on the target, bringing the bearing from centerline to zero, but they could never make the math work out right in the guidance system. The Sidewinder was the first to realize that the missile is closing in on the aircraft at some speed, and so really the angle it makes with the plane should be constant, not zero. This simplified the avionics enough to get a reasonably accurate missile.

https://en.wikipedia.org/wiki/AIM-9_Sidewinder#Design

Sidewinder was certainly not the first AAM to employ CBDR / collision-course guidance.

It was experimented since the late 1940s and early variants of the US Navy's radar-guided Sparrow employed it from 1953 as did the USAF's Hughes Falcon c. 1955. In fact Hughes engineers provided input on the technique to the China Lake Sidewinder team!

As one such pedestrian, this near-miss happens all the time, although half the time it's because drivers aren't even trying to look (e.g. a driver turning right will only be looking to their left while rolling through a stop).

So I find A-pillar design very aggravating -- though not as aggravating as drivers who roll up to and through stop signs at a constant speed approximately equal to my running speed.

My first exposure came from a relation of Werner von Braun witnessing a V2 launch or test. In one of the rare instances where von Braun did care where they come down,[1] he observed that the bearing to the rocket was constant -- that is, its course would bring it directly to his location.

He avoided death by diving into a ditch, if I recall. I think the story was told by Arthur C. Clarke.

I'd later encounter the concept in sailing training.

________________________________

Notes:

1. Allusion: Tom Lehrer. https://www.youtube.com/watch?v=TjDEsGZLbio

Driver training should teach you to 'lean and look', to move your head more than just rotating it left and right. This eliminates blind spots and once you pick up the habit you do catch the occasional cyclist or motorcyclist in a blind spot. They will often be stopped (or at least maintaining their position relative to yours) and looking at you, not expecting you to see them, and it's a nice shared moment when you make eye contact and they realise you actually checked.

    > Sometimes I wonder if I would have actually hit them if anyone would have believed I didn’t see them

As a daily motorcyclist that also drives a car, I'm uncomfortably aware of how much of your vision the A-pillar obscures. Not to mention the passenger side one, the B-pillars, and seating.

That said, it is as much my responsibility (or any road user, or pedestrian) not to put myself into a dangerous position as much as it is for you to do your best to keep an eye out.

It seems to be worse in newer cars. Most cars I've driven have been older models, pre-2000, every time I have to drive a new car, I'm always surprised at how bad the visibility is, they all have tiny rear windows and massive A pillars.

I used to own an old Datsun truck from the 1980s and the A-pillar blindspot was tiny because it had small, vertical A-pillars. A-pillars are a lot thicker and a lot more angled in newer cars.

This study [1] (from 2001) here goes into some details about A-pillar blindspots and how newer cars have worse visibility. I'm sure in the 17 years since the study was performed, cars have only gotten worse.

[1] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.884...

It sounds like what happens in every other instance of engineering: trade-offs. Emphasise performance in one metric -- preventing roof collapse and preserving the integrity of the passenger compartment in this case -- and it can come at the cost of other metrics (here, visibility). I don't think vehicle engineers are deliberately making cars hard to see out of, but I do think it's possible that those setting the policy which drives A-pillar thickness don't realize such is making cars less safe from a visibility perspective.

The cynic in me says that it's a liability thing.

Manufacturers are more likely to be liable if you roll your car and the roof caves in, killing you.

Manufacturers are less likely to be found liable if you couldn't see through your A-pillar and hit a cyclist, as apparently proven by the article.

It's very hard to point the finger at the driver for their roof caving in, there's nothing the driver can do to stop that from happening. But there's plenty a driver could do to avoid trouble from blindspots.

There has to be a solution where we can remove the A-pillars entirely and have a single unbroken window. I know it doesn't mean much, but I would pay significantly for that, for peace of mind and safety.

Airbags and crash test results are sales material, likelihood of running over a pedestrian is not. The incentives favor occupant safety over general safety.

My Prius has an airbag in the A pillar. What I find slightly terrifying is when you are turning you can get the same effect with a walking pedestrian. I'd frankly rather trade a thinner A pillar for a lower likelihood of clocking a pedestrian.

Same here, as a tall-ish person who likes to sit fairly straight up in the driver's seat, the rear-view mirror obscures my vision much more than the a-pillar.

I've learned my lesson. Now I do a little lean to look around the mirror at intersections.

Likewise. I don't know how many times I'd observed this phenomenon, and made the right conclusion (that thing's gonna hit me!). It was just another thing I intuitively did, without fully conciously knowing what it was or how to communicate it to others.

Knowing what it is now, and how it can happen in driving, gives me one more tool I can use to be a slightly less horribly dangerous driver on public roads.

It’s such a direct consequence of the principle of relativity that it seems weird to need a name fancier than “coming right atcha”.

Predatory animals, probably including humans, innately apply CBDR as a mental heuristic for catching prey and other objects.

  https://en.wikipedia.org/wiki/Gaze_heuristic

Reply on news.ycombinator.com