Thanks I can see how this works now. It seems to me now that the word "of" may be either redundant as in adding nothing to the information that is needed to achieve the answer but may be part of the stock of the cryptic language that compilers legitimately deploy
The road is, as another contributor has said, "quite small" but equally the word has been used to describe halves, quarters or even eighths of roads now I think more about it and has legitimacy in that respect
mop