However, as far as I can tell, the GPS data, in at least some cases, comes from Streetview-type camera cars which drive along the roads and capture the roadsign

However, as far as I can tell, the GPS data, in at least some cases, comes from Streetview-type camera cars which drive along the roads and capture the roadsigns. On French highways there are context-dependent speed limit signs which look exactly like normal signs but with a small additional panel below which tells you when they apply. Eg, big 70 in a round red circle, with a small picture of a car towing a trailer below. Eg https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Ftse1.mm.bing.net%2Fth%3Fid%3DOIP.zXrJslBWEkcATgzHIENzCgHaLj%26pid%3DApi&f=1 https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F... which obviously only applies to cars with trailers. Google maps (on my phone, not built-in to the car in any way) would constantly tell me that the speed limit of the road was that of the last such sign regardless of the specificity.