Highway is the opposite of Low. Low is related to Height. Height is etymologically related to High. High is similar to Broad. 
Route is a synonym of Path. Path is related to Direct. Direct is a synonym of Conduct. Conduct is a synonym of Behave. 
Highway <--Antonym--> Low <--RelatedTo--> Height --EtymologicallyRelatedTo--> High <--SimilarTo--> Broad 
Route <--Synonym--> Path <--RelatedTo--> Direct <--Synonym--> Conduct <--Synonym--> Behave 