The phrase "a primary route" is correct and usable in written English.
It can be used to refer to the main or most important path or method for achieving something, often in contexts like travel, logistics, or processes.
Example: "The city has designated a primary route for emergency vehicles to ensure quick access during crises."
Alternatives: "a main pathway" or "a key route".
"It has become a primary route".
The wide, flat valley of the Platte was a primary route of westward journeys in the mid-19th century; the Mormon and Oregon trails followed it.
The accident occurred in the Interstate 90 connector tunnel, which links Interstate 93 and the Massachusetts Turnpike with the Ted Williams Tunnel, and is a primary route to Logan International Airport.
In his wake, still life became a primary route toward the new, the abstract and the personal, as artist after artist -- van Gogh and Gauguin, Braque and Picasso, Matisse and Bonnard, Marsden Hartley and Stuart Davis -- arranged a few objects on tables by their easels and began to investigate their formal and emotional potential.
Context: Drug use is a primary route for the transmission of the Hepatitis C virus (HCV).
Language is a primary route, via inter-being, to community, and is core to our identity formation, our 'inter-are' state as part of a language community.
This made the sea passage across the Adriatic between Brundisium and Dyrrachium (or Apollonia) a link in the primary route for travelers, trade, and troop movements, between Rome and the East.
Inhalation of B. pseudomallei is a natural route of infection, and it represents the primary route of exposure in a deliberate biological attack.
Citrate synthase is a component of the glyoxylate pathway, the primary route by which acetate is assimilated in E. coli.
WHAT 6-bedroom house The west coast of Vancouver Island is on a primary migratory route for salmon going up and down the coast.
Inhalation is known to be a primary exposure route in humans and other mammals for Ni and Cr particulates.
