The Transport Agency will assess the damage to a bridge on the road that connects Marlborough with Canterbury.
A truck hit Wye Bridge in Wairau Valley between Blenheim and St Arnaud, on State Highway 63 early yesterday morning, and the driver was flown to hospital with moderate injuries.
The road has become the main highway after the Kaikōura quake closed the SH1 coastal route.
The number of vehicles using the route has soared, with Transport Agency figures showing the number of heavy trucks passing through St Arnaud a day has increased from about 40 to almost 600.
Road Transport Forum chief executive Ken Shirley told Morning Report some truck drivers were simply refusing to drive it.
"It was never designed to take the task that it's been asked to do now, and of course there's no alternative with the Kaikōura route being closed right through to the end of this year.
"So everyone's doing everything they can to make the best of a very inadequate road."
Mr Shirley said the cost of moving things through the South Island now is adding at least 25 percent to the bottom line of all goods.
The government is spending around $60 million to upgrade and maintain the highway.
Police said after the crash drivers had been directed through a ford with stop-go signs, and have been asked to only travel if necessary.
They said yesterday the ford was "swift but passable".
Engineers working to fix the bridge accidentally cut through a fibre-optic cable yesterday, causing banking and Eftpos outages in Marlborough.