primary route

In the Great Britain road numbering scheme, primary status is indicative of the importance of locations, with respect to road traffic.The status is awarded to settlements and structures of importance (the primary destinations) and to the roads that connect them (the primary routes).The status of both is maintained by the Department for Transport in combination with the Highways Agency in England and Wales and the Scottish Executive in Scotland. The concept was invented in the 1960s following the upsurge in inter-city travel in the country.
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The predetermined path of a message from its source, i.e ., sending or originating station, to a message sink, i.e. , receiving, addressee, or destination station. Note 1: In telephone switchboard operations, the primary route is the route that is attempted first by the operators or equipment when completing a call. Note 2: Alternate routing is based on network traffic conditions and supervisory policy. [From Weik '89]