KEY POINTS:
The North Island's main road and rail at Marton could be cut off for three days after a truck crashed into a rail bridge last night.
Diversions are in place for motorists and alternative arrangements have been made for train passengers but delays can be expected.
The driver of the truck was described by police as "safe and well" after the crash on State Highway 1 near Marton last night.
Police and engineers were at the site this morning assessing the damage to the bridge and the road.
Acting Sergeant Paul Johnson said there was "extensive" damage to the main span of the bridge and it would be closed for a minimum of 48 hours.
Mr Johnson said State Highway 1 would probably be closed for as long as the bridge.
"The bridge goes over the road unfortunately, and it's structurally unsafe and there's things hanging off it, and a lot of debris on the road."
He said a diversion was in place but police had concerns about traffic on Friday evening, which was typically heavy.
"What we want people to do is be very conscious about their speed in that area because the detour is not a highway. It's quite narrow and windy."
Toll NZ spokeswoman Sue Foley said the company was hoping the overbridge would reopen in two days, but it could take three.
"It's impacting about 14 trains a day which includes the (Wellington-to-Auckland) Overlander service, so we're having to bus passengers between Palmerston North and National Park," Ms Foley said.
Freight was being transported via an alternative line between Taumarunui and Stratford.
"But it is a very lengthy by-pass, and there are some tunnel restrictions with the larger freight carriages."
Ms Foley said Toll staff were well-prepared to cope with the re-route, after major flooding caused similar problems in 2004.
David George, chief executive of national rail provider Ontrack, said the accident highlighted the need for truckies to take more care when loading their vehicles.
"It appears that a load being carried by a south-bound truck has hit the bridge beam, spilling the load onto the highway and into the path of an oncoming north bound vehicle," he said.
"That vehicle has hit the centre-lane pier of the bridge, caught fire and severely damaged the track."
Mr George said bridge-strikes by trucks were an continuing problem for Ontrack, and happened up to 30 times a year.
Mr George said Ontrack was not trying to "get at" truckies, but needed their cooperation because structural damage might not always be apparent.
"The most important thing for them to do if they hit a bridge is to report the strike to Ontrack... even if they don't think any damage has been done."
There were potentially catastrophic implications when a bridge was weakened because it could later collapse when a train was crossing, Mr George said.
"If this happened when a passenger train crossed, the consequences are unthinkable."
- NZPA
