Category:Derivative highway designations

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When highways leave their jurisdiction of numbering and continue straight on, their number is sometimes retained. This can also occur across national borders, such when a U.S. highway connects directly with a route in Canada or Mexico. Another case of derivative highway designations could be designations in the same numbering jurisdiction prefixed or suffixed with the number of the parent route (e.g. 3-digit Interstate).

Some highway numbers are also derived from roads they upgrade or bypass (in the case of many 400-Series Highways), or follow very closely for most of their distance (Quebec Autoroutes).