After whom was the road named? 
If one of the family fought or was a general of distinction in that war with Lord Elgin that might provide an explanation, as would an Arbuthnot in the Colonial service. Possible candidates are the Generals
 Charles George Arbuthnot 1824-1896
 Charles George James Arbuthnot 1801-1870
 George Alexander Arbuthnot 1830-1896
 George Bingham Arbuthnot 1803-1867
 Henry Thomas Arbuthnot 1834-1919
 Robert Arbuthnot 1773-1863
 Thomas Arbuthnot 1776-1849
 William Arbuthnot (Major-General) 1838-1893

It was not named after John Bernard Arbuthnot (1875-1950), ADC to Governor General, HK because it is mentioned in documents dated 1874. -