The Government estimated that the safety measures, once fully rolled out, would prevent the deaths of 160 people.
Ardern gave the example of the new barrier that had been installed on State Highway 3.
She said it had been hit roughly 40 times already – "potentially preventing at least that many deaths and serious injuries".
Despite this, Twyford went on the offensive when talking to media.
"The Opposition will say we should be building four-lane expressways instead."
But Twyford said just 3 per cent of all deaths and serious injuries over the last 10 years happened on those 11 routes that the National Party wants to be turned into uneconomic motorways.
"Our Government is taking a balanced approach."
He said the Government was spending more on local roads and state highways than the last government did.
Associate Transport Minister Julie Anne Genter said the Government believes it is unacceptable for anyone to be killed or seriously injured on our roads.
"Most roads deaths and serious injuries are preventable and too many New Zealanders have lost their lives or been seriously injured in crashes that could have been prevented by road-safety upgrades.
"We are taking a balanced approach to making our roads safer – investing significantly more in safety improvements, increasing safe driving messages and investigating lower speed limits only on the most dangerous roads in the country."