There's nothing special about dual carriageway. A carriageway is simply a way that is wide enough and smooth enough for a carriage to pass. It's still a useful

There's nothing special about dual carriageway. A carriageway is simply a way that is wide enough and smooth enough for a carriage to pass. It's still a useful distinction because cars have the same requirements, but "carway" sounds silly. The word road comes from the word ride which is still used today to refer to bridleways in Britain (for example, in Hyde Park: the North Ride and the South Ride). Road is therefore a much more general word and is used to refer to many more things than carriageways like railway lines, tunnels and even areas of water near shores. As for the other stuff, it's true that British and American have both diverged from a common root. The best example is with -ise or -ize endings. Neither is completely correct because some words originally had one and some had the other. The Oxford English Dictionary reflects the original endings in its spellings. But at some point Britain standardised on one and America standardised on the other. Maybe -ise looks nicer but -ize looks cooler? Who knows...