The highway begins as Bangor Road just west of Darfield town centre, and proceeds in a westerly directions towards the mountains through flat pastoral farmland. Just before reaching the foothills, the road intersects with the Inland Scenic Route coming from Waddington and begins its concurrency at Homebush. After a name change to Homebush Road, the road skirts to the north of Coalgate and then to the south of Glentunnel before veering left and narrowing to one lane to cross the Selwyn River. Now known as Wairiri Road, the road widens back to two lanes and passes through undulating to hilly farmland. At Glenroy the road changes name to Windwhistle Road and climbs towards the settlement of Windwhistle. Beyond Windwhistle, the name changes to Rakaia Gorge Road and begins a spectacular descent into the Rakaia Gorge. For most of its length the Rakaia River runs on shingle river beds as a braided river but here the river is mostly a single channel. The river here has carved out the surrounding land to form two level terraces. The road passes over both these terraces before narrowing to one lane again to cross the river. After widening again, the road changes name to Arundel Rakaia Gorge Road and rises towards the plains again. The road emerges onto the plains but passes right underneath the towering Mount Hutt. The road is frequently covered by snow and ices over in sheltered areas during the calmer periods of the winter months in higher parts of the road. The road turns left onto Waimarama Road10 km north of Alford Forest and proceeds through arable farmland, changes name again to Mount Hutt Station Road and arrives in Methven, where it changes name again to Main Street. After Methven, the road changes name to Methven Highway and proceeds in a south to southeasterly direction through more pastoral farmland. Before Ashburton, the road hugs the Ashburton River, the name of the road changes to Alford Forest Road for about 2 km, then to River Terrace for 600 m and lastly to Moore Street for the last 300 m of the route before terminating at SH 1 in the town centre.
Route changes
When SH 72 had its state highway status revoked, SH 77 was extended to cover the section between Mount Hutt and Waddington. In 1997, SH 77 was diverted at the intersection of Homebush Road, along Bangor Road, to terminate with SH 73 at Darfield.
