It's all part of the New Zealand Transport Agency - Waka Kotahi's Road to Zero vision - the aspiration that no-one is killed or seriously injured in road crashes.

One of the changes affects a section of State Highway 1, just 190 metres long, in South Canterbury's Winchester. The speed limit used to be 100km/h, but has now been halved.

Then there's the 30 kilometre-long chunk of State Highway 2 between Katikati and Tauranga, where speed limits are now set at either 60 or 80 km/h.

But by far the longest and most substantial change to have been made by Waka Kotahi is the 110 kilometre-long State Highway 6, between Blenheim and Nelson.

There, speed limits now never reach 100, and alternate mostly between 90 or 80km/h.

But the changes haven't gone unnoticed by locals.

"When's 90 been a speed limit?" asked Seddon resident Moana Johnsen.

• Waikato, Bay of Plenty, 110kmh speed limit roads prove safer than regular highways
• Police officer busts the ‘speed kills’ myth
• Auckland man wins years-long speeding ticket case after police can't find evidence
• NZTA agrees speed limit through Burkes Pass 'not safe'

"We've got decent vehicles, that stick to the roads, and we've got to do 90? 90 in an open space?

"And then there's 80 and then there's 60 going up a hill that's got an overtaking space? Yeah nah, it's revenue gathering, mate, revenue gathering."

Johnsen made the State Highway 6 journey four times over Christmas - and each time, was frustrated at the new limits.

"Christmas Day we must have spent quite a bit on it, and you know, the young people that were there, the 20s, 30s year-olds, they were like, 'This is not fair'... they've all got nice cars and stuff."

She said she was worried about the overall trend.

"They've done all these changes further down the road, the Kaikōura coast, which has been fixed up and made really nice.

"But they've got signs up there too: 60, 80. Is the open road going to go to 80?

"It's ridiculous, might as well get my horse and cart out and trot up and down the road. If our roads are not up to 100km/h, then fix them."

But Waka Kotahi said making sure speeds were safe was the quickest and most effective way to prevent deaths and serious injuries.

In a statement, an agency spokesperson said safe speed limits minimised the severity of crashes when they occurred.

"[The] Agency is currently identifying roads where reviewing speed limits could make a big difference in preventing deaths and serious injuries, and where communities are calling for change.

"Any proposal to drop speed limits is driven by the need to improve safety and reduce harm for everyone on our roads."

But road safety charity Brake NZ director Caroline Perry said many more roads needed to be looked at - and not just state highways.

"We still see at the moment a significant proportion of roads in New Zealand that have speed limits that don't match the condition of the roads," Perry said.

"A lot of the more rural roads that are windy, narrow, single or dual lane, they're just too fast for the conditions of the road that we have at the moment."

She did think that was changing - and speeds were coming down, but not fast enough.

Gisborne District Council recently signalled their intent to lower speed limits, both for Gisborne's urban roads, as well as for Tairāwhiti's rural roads.

It follows the reduction of all of Wellington's CBD roads from 50km/h down to 30km/h last year.

But Perry said it was difficult for councils - who set the speed limits for all roads which aren't state highways - to change speed limits.

She wanted to see the process simplified so it can happen quicker.

"The easier that it is for councils, that is certainly a bonus in terms of getting it through quickly. The other key part is to engage communities as well, talking to them about the speed limits in their areas, talking through the reasons why actually those changes in speed limits are necessary and actually the difference it can make."

Waka Kotahi said it was intending to make it easier for local authorities to change speed limits.