California AB 2047 makes 3D printers off-limits to students, educators, business

About 15% of rural Americans aren't within 25 miles of any intercity transit, much less interstate; low-income residents are disproportionally represented in that group. That figure jumps to 25% if you exclude suburbs, and in some states that figure is as high as 62%.[2]

Even as intercity bus demand has increased due to the declining quality of air travel in the US,[3] rural intercity bus access has declined. Greyhound served many rural routes until its slow collapse before being acquired by FlixBus, which is more focused on urban access than Greyhound was. The deregulation of intercity bus access in 1982, which led to the closure of many intercity routes (disproportionally in the rural Midwest) that required subsidization from more profitable routes, was a major factor.[4]

So "what percentage of Americans can't afford a bus ticket to the nearest city in an adjacent state" is a non-starter of a question, because most of the Americans who'd _need_ an interstate bus ticket can't even get to a bus stop without first owning a car... with which they could simply drive to another state.

1: https://itdp.org/2024/01/24/high-cost-transportation-united-...

2: https://www.bts.gov/data-spotlight/85-rural-residents-have-r...

3: https://www.wsj.com/lifestyle/travel/bus-travel-tickets-airl...

4: https://www.thenation.com/article/society/greyhound-bus-tran...

Other countries regulate the pressure-bearing parts instead. It probably started off with a safety rationale (those parts are generally proof tested), but those parts ALSO tend to be the ones that are more difficult for someone to produce at home.

They will refuse to print images that contain the EURion constellation, a cluster of points with specific distances between them. (https://en.wikipedia.org/wiki/EURion_constellation)

More generally, "Does this image represent US currency?" and "Does this 3D mesh represent a dangerous gun part?" are different kinds of questions.

Checking if an image is US currency is simple. Not only can an image similarity hash be used, but the design of the currency can be changed to make checking easier. The checking program just has to run a textbook algorithm and compare the result with a handful of hashes (we only have a few denominations of bills).

We can be confident that the checking program will always see substantial portions of the bill, so it can always see the pattern. If someone chopped the bill into tiny pieces, it would look fake when glued together. Looking like a real bill is the thing we want to control, and that's something we can reliably measure with simple algorithms.

Checking if a 3D shape is a gun part is an unsolvable problem. (It would be equivalent to making a program that can detect hidden "subversive" meanings in text.) The checker would have to understand how the piece could operate in the hands of a skilled person. Parts could be printed in multiple pieces, or have material removed after printing, so it'd have to anticipate all possible post-processing steps.

Even if the problem is limited to "match against these known gun part hashes", gun parts are not defined by their overall appearance. The files can be mutated until they no longer trip the detector, yet can be easily post-processed into functional components. (Also, a similarity hash for 3D toolpaths may not exist.)

(Such a hashing regime would be useless to stop "3D-printed guns" as a concept, because the design could be changed to not match the hash at all, without post-processing.)

Looking at just the silhouette or shape, you couldn't really tell the difference between the body of a firearm that was later going to receive a metal tube from the hardware store or a plastic bracket that I'm going to use to support a shelf.

And even if you could accurately tell the difference, how do you know I'm not helping my nephew build a Nerf gun?