"Originally the guide was aiming to target 5 per cent of the roading network with the highest safety benefits, then that was increased to 10 per cent," said Mike Noon, AA's motoring affairs general manager.
"Now some areas are looking to change speed limits on the majority of their roads while others are picking out a few bits and pieces.
"Some are using the guide's recommendations unchanged while other places have adjusted them, so it's inconsistent," Noon told the Herald.
He also suggested some councils might be taking the easier option of reducing speeds rather than upgrading roads to make them safer.
"We have seen little of this coming through in proposals so far and we are concerned that we are going to just see limits coming down across the country."
Check the interactive graphic below to see fatal and serious crashes on NZ roads since 2000 and how current speed limits compare to the safe and appropriate speeds suggested by Mega Maps.
Road deaths since 2000
Each red dot on the map shows one fatal road crash. Zoom in to explore.
Serious injuries in road crashes since 2000
Each purple dot on the map shows one serious road injury crash. Zoom in to explore.
100km/h speed limit
NZTA's Mega Maps planning tool estimates 95 per cent of NZ's open road should have a lower speed limit than 100km/h. Drag the slider from left to right to see how many roads are affected.
50km/h speed limit
Mega Maps also estimates many urban roads should have speed limits lower than 50km/h. Drag the slider across to see how almost two thirds of Auckland roads are affected.
Explore the interactive map
Noon also questioned whether the road-using public were being sufficiently consulted on proposed changes.
"Whether a change to the speed limit makes sense to people or is supported by the public seems to not really matter under the guide, which questions the point of having consultations on these issues at all if the outcome is already determined," he said.
The AA has written to Genter seeking a review of the guide.
Communities must be consulted
The New Zealand Transport Agency, which developed the guide and administers Mega Maps, said that when carrying out public engagement on proposed speed limit changes, it and other RCAs provided a range of information including the "safe and appropriate speed" calculated for the road being consulted on.
"When reviewing and setting speed limits, councils and the NZTA need to bring communities along with us by having open and honest discussions about speed, listening to people and understanding different perspectives, so that when a decision is made to change a speed limit people understand why the change is being made," said Niclas Johansson, NZTA's acting director of safety and environment.
The NZTA, as a road-controlling authority, also seeks public input when reviewing speed limits on state highways, for which it has responsibility.
"As well as the technical inputs on what is a safe and appropriate speed for a state highway, we also engage with communities at an early stage to better understand how people use the road and what other factors might ultimately influence safe speeds and speed limits," Johansson said.
"Communities typically tell us that increased traffic volumes, new developments such as a shopping centre or sub-division, a new school, increased number of tourists, or a greater number of cyclists are all factors that influence their views on safe speeds."
Johansson said that in many cases, speed reviews were initiated because of community feedback or concern.
Genter said she also received a lot of correspondence from communities and local authorities that wanted safer and more appropriate speeds in their area.
"Up until now it's actually been difficult for them to implement the speed limit they want," she said.
Auckland Transport has proposed cutting speeds on 700km of high-risk roads including urban, rural, town centres and the Auckland city centre. It estimates the changes, to be made under the Speed Limits Bylaw 2019, would affect about 10 per cent of the region's local road network.
Public consultation on the proposals closed on April 1.
A survey of Auckland AA members showed 62 per cent were opposed or strongly opposed to a proposed 30km/h speed limit for the entire CBD.
"People see 30km/h as too slow to be credible on all but a very small number of CBD roads, and they're not at all comfortable with that becoming the default limit for the whole area," AA spokesman Barney Irvine said.
Michael Brown, an AT road safety engineering team leader in Rural Safety and Regional Speed Management, said the agency's focus was on getting the greatest return on death and serious injury reduction. That is an estimated 30 per cent reduction on the roads it is focused on.
Upgrades to the roads are also on the cards but will be more difficult and more costly.
"Even with engineering up we may still reduce the speed limit because what we might be doing is engineering up to an 80km/h rather than a 100km/h road," Brown told the Herald.
Brown said Mega Maps was only a guiding tool.
"We've got a lot of faith in the methodology behind the programme."
Other councils are also considering or making changes to speed limits based on the programme.
Waikato Regional Council was the first to use the Speed Management Guide in 2016. It has adopted a second round of changes.
Hamilton City Council is reviewing is speed limits at present.
Waipā District Council is proposing more than 200 changes to speed limits on roads to improve road safety.
Western Bay of Plenty District Council, New Plymouth District Council, Napier City Council are reviewing speed limits.
Hastings City Council made speed limit changes in 2018.
Whanganui City Council has made changes to some speed limits and is considering others.
Horowhenua District Council is reviewing rural speed limits before moving on to urban roads.
Wellington City Council has already reducing speed limits in some areas and is considering others.
Grey District Council reviewed some urban speed limits last year.
Westland District Council is trialling lower speed limits on a number of roads until May 31.
It has said initial public feedback has been overwhelmingly positive and areas that were not part of the trial were also being considered.
Tasman District Council has reduced speeds on a number of roads that intersect with a crash-prone section of SH60.
The speed limits on nine roads were reduced from 100km/h to 80km/h when the NZTA cut the 100km/h on the section of SH60 by the same margin.
Christchurch City Council is able under a 2017 bylaw to change speed limits within the city and has been doing so over a number of years. It also has the ability to review the limits every two years.
At present it is proposing to reduce the speed limit on the Summit Rd from 100km/h to 60km/h.
Selwyn District Council reviewed its speed limits in 2017 and has rolled out a number of speed limit reductions.
Waimakariri District Council has done the same.
Queenstown Lakes is consulting the public on proposed changes to speed limits around the region. Closes in May with hearings in June.
The new Speed Limit Bylaw 2019 would reduce several speed limits across the district and make some temporary reductions permanent.
Dunedin City Council has already reduced some speed limits in urban areas and is rolling out other changes.
Waitaki District Council is also consulting on proposed speed limit changes.
Southland District Council revised its speed limits in 2015.
Invercargill City Council also revised its speed limits in 2015.