pertaining to a journey, travelling, or route ...1801 rare
a person who itinerates; a traveller ...1822 rare
from Latin itinerārius (pertaining to a journey) + -an
FIRST DOCUMENTED USE
1801 - see EXAMPLE below
"...A Polymetrical Table, Shewing the Itinerarian Distances, in British Miles, between some of the most remarkable Places of Hindustan..."
From: The Asiatic Annual Register: Or, A View of the History of Hindustan, and of the Politics, Commerce, and Literature of Asia for the year 1800