The Collaborative International Dictionary of English v.0.48:

Highroad \High"road`\, n.
   A highway; a much traveled or main road. [Mostly British]

   Syn: trunk road.
        [1913 Webster]

WordNet (r) 3.0 (2006):

highroad
    n 1: a highway [syn: highroad, trunk road]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "highroad":
   Autobahn, US highway, alley, alleyway, arterial, arterial highway,
   arterial street, artery, autoroute, autostrada, avenue,
   belt highway, blind alley, boulevard, bypass, byway, camino real,
   carriageway, causeway, causey, chaussee, circumferential, clarity,
   clear coast, clear road, close, corduroy road, county road, court,
   crescent, cul-de-sac, dead-end street, dike, dirt road, drive,
   driveway, ease, easiness, easy going, effortlessness, expressway,
   facileness, facility, freedom, freeway, gravel road, highway,
   highways and byways, intelligibility, interstate highway,
   lack of hindrance, lane, local road, main drag, main road, mews,
   motorway, parkway, pave, paved road, pike, place, plain sailing,
   plane sailing, plank road, primary highway, private road,
   right-of-way, ring road, road, roadbed, roadway, route nationale,
   row, royal road, secondary road, simplicity, smooth road,
   smooth sailing, smoothness, speedway, state highway,
   straight sailing, street, superhighway, terrace, thoroughfare,
   through street, thruway, toll road, township road, turnpike,
   uncomplexity, uncomplicatedness, wynd