Comment by manarth
6 hours ago
"it's unclear what the lawmakers, road designers, and police intend"
In many cases, there's a gap between the original intention and the current need.
Many speed limits and policies were established in an era of fewer cars, but also much less capable cars with fewer safety features - many speed limits were established before the adoption of ABS, stability control and airbags, and more recent innovations in lane-keeping and adaptive cruise control.
Modern cars may be capable of travelling at greater speeds with greater safety, but there's a more recent recognition of the increase in emissions pollution from increased speed. Speed-limits typically remain grandfathered in at their original value (which may have been set 30, 40, 50 years ago), regardless of the change in context.
Then there are some pecularities such as the UK default of 60mph for a single-track road, but if you were to try that in many rural locations (think Cornwall, Scotland, Wales) you would likely find yourself upside-down in a ditch.
This post highlights the absurdity of some of the limits!
https://www.reddit.com/r/CasualUK/comments/1dng5z9/genuinely...
The UK NPCC (National Police Chief's Council) have a published policy where enforcement effectively starts at 10% +2mph over the speed-limit (whilst allowing officers to use individual discretion if they feel there are aggravating factors).
https://library.college.police.uk/docs/NPCC/Speed-enforcemen... [PDF]
Counterpoint: with mobile devices, and increasingly, control and information features of automobiles themselves, distracted driving is increasingly a concern.
There's also the point that driving capabilities vary wildly by individual, and often decline drastically with age. Recent case-in-point, an elderly driver in San Francisco who killed a family of four (a mother, father and two daughters, waiting at a bus stop, not in the roadway at all), let off with a minimal sentence, raising much public furore:
<https://www.sfchronicle.com/crime/article/sf-west-portal-cra...>
<https://www.sfchronicle.com/crime/article/san-francisco-west...>
The driver was speeding (70 mph in a residential area), and possibly driving the wrong way on the street.
> Speed-limits typically remain grandfathered in at their original value
That depends on where you are. In Texas, state highway speed limits are determined though a traffic study[1]. The monitor traffic for a while, then set the limit to the 85th percentile.
People can use this to get out of speeding tickets. If you find that it's been a long time since a speed study was done on the road you were on, the judge might throw the ticket out.
There are some hard limits though. For example, the maximum speed limit that can be set on a road is 85 mph.
[1]: https://www.txdot.gov/safety/driving-laws/speed-limits/speed...
In other words, 15% of people are ALWAYS speeding, by definition.
So with perfect enforcement (punish everyone over the threshold), how do you enable an 85th percentile rule?
> 15% of people are ALWAYS speeding, by definition
Not necessarily. If the data is heavily clustered around a single value, the percentile collapses to that number.
> UK default of 60mph for a single-track road, but if you were to try that in many rural locations (think Cornwall, Scotland, Wales) you would likely find yourself upside-down in a ditch.
The way the national limit is framed is more limit than road speed. It's interesting how we think of the limits as drivers: we get frustrated when other people go slower than the limit, we don't treat it as a limit, we treat it as the speed you should be traveling at.
I live fairly rural in New Zealand (UK expat) and even though you necessarily get a lot of speed variation on the roads around me, due to being winding, having farm traffic, sometimes narrow, you still get idiots who have to be going at the exact limit (or over) and tailgate 1m behind any vehicle in their way. Including trucks who can't really see them when they do that. I enjoy driving fast on those roads but I still don't understand the impatience.