But it is an alpine highway, so avalanches can seriously affect the road between Te Anau and Milford sound.
An avalanche control programme has been in use for many years and it was in operation yesterday.
Heavy snow leading to avalanche risk had closed the road at the weekend and it was closed again at 4.30pm on Tuesday.
Work was done by the Milford Road Alliance yesterday to clear the road of any avalanche threat and the road was reopened at 2pm.
A Waka Kotahi NZ Transport Agency statement said the avalanche area covered 17km, starting at Falls Creek, above Hollyford Rd junction, and ending at the Chasm on the Milford Sound side of the Homer Tunnel.
The terrain of near-vertical walls and large, steep snow basins alongside the road provides an almost perfect landscape for avalanches.
The avalanches start high up in the mountains, which cannot be seen from the Milford road.
The Milford Road Alliance operates an avalanche control programme that predicts and controls avalanches.
A specialist avalanche control team employs highly technical equipment to manage avalanches.
The specialised weather and condition monitoring equipment is based both at road and mountain level, and is monitored around the clock to maximise safety and minimise road closures.
Besides predicting avalanches, the programme also controls the avalanche hazard by either not allowing traffic to stop inside the avalanche area or closing the road and using controlled explosives to release avalanches before they occur naturally.
Controlled explosives were used yesterday morning to move snow down from the mountains.
Helicopters were used to ferry the explosives high up in the mountains and reduce the avalanche risk.
By 2pm yesterday the risk was reduced and the road was reopened.
