Why do American road signs use so many words where most of the world uses a picture?

The argument made in favour of the text version, which I heard often in the trade, is that words are precise in a way symbols are not.

A symbol has to be learned and it can only express so much. "No turn on red" is a conditional rule about a specific manoeuvre in a specific signal state, and there is no obvious picture for it. American signage leans on wording partly because the underlying rules are more conditional — regulations vary by state and by intersection, and text scales to that in a way a fixed symbol set does not.

The counter-argument is exactly what you noticed: reading takes longer than recognising, and at speed that gap is the whole safety question. The compromise you see in practice is that the shape and colour do the fast work — an octagon means stop before you have read anything, a yellow diamond means warning — and the words carry the detail.

There is a specific historical fork rather than mere inertia.

Most of the world's pictogram signage descends from an international convention on road signs and signals agreed in the 1960s, which standardised shapes, colours and symbols across signatory countries. That is why a European driver can cross six borders and read every sign without knowing a word of the local language.

The United States never adopted it. It has its own national manual instead, which predates the convention in spirit and evolved separately, and Canada, Australia and a few others follow the American approach more closely than the European one despite geography suggesting otherwise.

So the two systems are not one standard applied loosely; they are two standards that were already established before anyone tried to merge them, and by then every road in both blocs was already signed.

On whether it causes problems: the honest answer is that it is a smaller problem than it looks, for reasons that are specific to the country rather than to the system.

The overwhelming majority of drivers on American roads read English well enough for a three-word sign, and the roads that carry the most international traffic — interstates, border crossings, national parks — have been steadily gaining symbols for decades. The pedestrian, cyclist, deer crossing and no-entry signs are already pictograms.

Where it does bite is rental drivers on unfamiliar rules. "Right turn on red is allowed unless a sign forbids it" is a rule most visitors do not know they need to look for, so the sign forbidding it is doing double duty: it has to teach the default and then contradict it, in a language you may not read, at a junction you are already navigating.

Fun detail that goes the other way: some American signs are more legible to a foreign driver than European ones, because the convention's symbols are not as self-explanatory as their fans claim.

Ask a group of new drivers what the European sign with a red circle and a black car overtaking another car means, or the one that is just a white circle with a diagonal band. Most can guess the first and almost nobody gets the second right without being taught it. Symbols still have to be learned; they only feel obvious once you have.