A wire-rope barrier on a busy, scenic stretch of road north of Wellington has potentially saved dozens of lives over the past decade by halting deadly head-on crashes.

The barrier stretches for 3.4km along Centennial Highway on the Kapiti Coast, on what was a notorious section of road.

In the decade before the first part of the wire went up in 2005, 16 people were killed and 14 seriously injured in 15 major crashes.

The $15 million barrier was extended in 2007 and since then there have been no deaths or serious injuries on that part of the highway.

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Figures released by the NZ Transport Agency today reveal in that time the barrier has been struck 122 times.

"Each one of those times represents a potentially tragic crash averted," said Mark Owen, the agency's regional performance manager.

One of those crashes is shown in footage obtained exclusively by NZME News Service. In the vision a grey car hits the wire, averting what would have been a head-on crash with a white van travelling north on New Year's Day.

Such head-ons saw calls grow for a divider to be installed and in 2005 coroner Garry Evans added his voice to the clamour, saying it was a matter of urgency.

Centennial Highway is one of the busiest two-lane roads in New Zealand, with more than 20,000 vehicles taking its narrow 80 km/h passage every day.

"The barrier, when installed, was a challenging exercise, given the narrow corridor between the sea and the hillside," Mr Owen said.

"At the time it was built, it was the first barrier of its kind on a two-lane road in New Zealand."

Mr Owen said the transport agency was working to reduce "avoidable deaths and injuries" on the country's roads.

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"Drivers make mistake, and drivers can also be affected by medical conditions - but roads and roadsides can be designed to help prevent these from resulting in fatal crashes."

The transport agency says median barriers will also separate traffic on the Kapiti Expressway and Transmission Gully, two roading projects for traffic heading in and out of Wellington. Both are due to be finished by the end of the decade.