Thursday, March 7, 2019

Is driving 5 mph over the speed limit ‘reckless’ ?

An online acquaintance from Great Britain posted this article, titled “Retired village couple catch 130,000 speeding drivers in just a week,” with the caption, “Should motor-vehicle offenses be higher up the law enforcement agenda?  A long debate thread ensued, which I will not reproduce in full.  Instead, I’ll highlight a specific exchange I had with one reasonable commenter, and let you be the judge.  All names are changed as usual.

Kevin: That's approx 1 driver every 5 seconds speeding, 24 hours a day, 7 days a week. I somehow doubt this.

Me: They are plainly lying, just mathematically speaking. Even if they weren't, they're wasting their time and energy without performing any important public service at all. Speed limits are too low, more like guidelines than actual limits, and everyone in every developed country on Earth seems to know that except these two.

Kate:  lmao at the extraordinary defense of reckless driving practices in this thread…People who don't get the difference a couple of miles p/h can make to vehicle accidents honestly need to go back to school and pay attention. Makes me so fucking angry.

Me: if you think driving 5mph over the speed limit is reckless driving you're just amazingly out of touch with how ordinary people drive. 5mph over is the *norm* - the speed of traffic. Going considerably slower than the speed of traffic poses more safety risks than it does to just keep pace; it's oftentimes safer to go 5 over than it is to go 5 under. And in any case, that norm evolved because cops everywhere realize speed limits are drawn arbitrarily along a spectrum of risk (as opposed to some objectively correct cutoff point) in a way slightly more risk-averse than the average person's risk tolerance, including theirs, which makes those laws particularly lacking in moral authority at the margins. This universal speed limit fudge factor is not a consequence of individual moral failings; it's a direct and predictable consequence of arbitrary, out-of-touch, overly restrictive regulations, which is replicated in other areas.

If you want the moral authority to finger-wag at people who go a tiny bit over the limit, you need to boost the limit to something approaching popular consensus on what actually constitutes unsafe driving. We can either a) boost all speed limits by 10-15mph if you want them rigidly enforced, or b) keep the status quo of "unwritten rules" in which you're only pulled over for speeding if you're going more than 10 over (unless the cop's in a particularly bad mood!)

Kate: I'm actually really glad you used 5 mph as an example. Here's a video that pretty acutely explains the difference between car accidents just 5kmph in difference. If this is the damge 5kms can do, imagine how much worse 5 miles is. 

Me: There are a few reasons that video makes for an unconvincing rebuttal to my argument:

1. Determining whether something is reckless (aka "unacceptably risky") requires not just an analysis of how bad the event would be were it to happen, but also of how likely it is to happen in the first place. Yes, if a truck unexpectedly pulls out in front of you, it'd be better to be going 60. But the likelihood that this will happen is very low, and also variable based on circumstance (are you near an intersection? are the roads crowded or empty? is it night time so you'd see the headlights? etc.) in ways fixed speed limits do not account for.

2. In this video, the distance between the braking car and the truck was reverse engineered to maximize the difference in speed at impact (or at least inflate it beyond what it would usually be) for the purpose of making a more powerful commercial.

The video's core insight is that "in the last five meters of braking, you wipe off half your speed." Logically, this exponential speed decrease will only occur in one instance without occurring in the other under a narrow subset of real-world braking distances. Suppose it takes 45 meters to brake at 60kph, and 56 meters to brake at 65kph (reasonable because I looked it up: In both cases, you wipe off half your speed in the last five meters, fine - but that only makes a big difference in velocity at impact if your vehicle happens to be between 40-56 meters away at the moment you see the obstacle. Beneath 40m it makes little difference, and above 56m it makes no difference at all. Drivers already intuitively realize that the risk of *any* need to brake to a full stop is pretty low. The risk of encountering an obstacle exactly 40-56 meters away is lower still.

3. However important 5 kph/mph may be, speed limits are still an arbitrary cutoff, making them largely lacking in any real moral authority. The difference between 60 and 65 may be important, but it's not any MORE important than the gap between 60 and 55, or between 65 and 70, etc. Somebody still has to draw a line saying "this level of risk is acceptable, while this level is not" - and reasonable people can disagree about where that is! The reason speeding is so prevalent is not because average people are morons, incapable of grasping the gradual but intuitively obvious relationship between speed and risk, who need stern government technocrats to protect them from themselves. It's because speed limits were set by people from bygone eras, in which modern ABS and car safety features were not available, who faced political incentive to prioritize safety over competing values like tolerance and time efficiency, and were consequently much more risk-averse than the population is today.

4. Drivers do not drive in a vacuum, and the optimally safe speed is dependent on the speed of cars around you. Stop-times are not the only factor in driving safety; others include safe merging, or changing lanes on a busy highway, which are much more easily accomplished if your position in relation to other cars remains relatively constant. The fact of the matter is that most people speed whether you like it or not, and responding to this by being that one puritan asshole going way slower than everyone else ENDANGERS those who must now react to the unexpected, feel compelled to pass, or get over to the side in order to make their exit.

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