112 works in the reverse way in the US as well (along with 999 which is the equivalent in many other countries such as the UK). There's not really any reason not to have many numbers just in case. Tourists shouldn't have to memorize, and recall, new numbers in an emergency.
As siblings have commented, 112 and 911 are in the GSM standard. On landlines, only 112 will work in most EU countries (and even that is an EU achievement; e.g. in Switzerland 112 is inconsistent)
What else would someone who dials 911 be trying to achieve? And does the benefit outweigh the cost?
911 has enough mindshare that it'd be silly to use it for anything else. And if you're not going to use it for anything, a redirect seems like a very productive way to park it.
Sure. And in a spherical cow world, assuming you want to make n emergency numbers work, you'd sort by population-using and take the first n.
…but even then 911 would only be an emergency phone number if n ≥ 3; first two places being taken by 112 and 110 (because China).
However, this completely ignores facts like people from China being far less likely to travel to e.g. the US… it's more of a "of the people who'd make emergency calls in XYZ, what numbers would they use" consideration…
…it's really not an easy question. GSM went with 112 and 911 and I guess that's as good as an answer this'll get.
