Most speed limits around the country are considered too high and some face cuts within the next three years as the Government aims to crack down on the rising road toll.
The NZ Transport Agency (NZTA) estimates about 87 per cent of speed limits are too high for the conditions.
The most dangerous roads - 10 per cent of the state highway and local roading network - may see speed limits reduced over the next three years, as the NZTA looks to reduce the greatest number of road deaths and serious injuries as quickly as possible.
Its Mega Maps online risk assessment tool - which is being used by NZTA and councils as a guide for deciding on new speed limits - suggests only 5 per cent of the open road should have the current 100km/h posted speed limit.
Instead, Mega Maps suggests a safe and appropriate speed of between 60 and 80 km/h would apply to most stretches of open road.
For most urban areas, the safe and appropriate speed would be between 30 and 40km/h. In Auckland, for instance, 65 per cent of 50km/h streets would require a lower speed limit, usually 40km/h.
The Mega Maps tool uses a range of factors such as crash history, road conditions, surrounding land use and traffic volumes to calculate the theoretical ideal speed. It is designed as a planning tool, not a blanket speed limit recommendation, and the Automobile Association has questioned whether councils are using it correctly.
But transport planners are under pressure to act fast on the road toll, which reached 168 after six people died over Queen's Birthday Weekend. Four drivers, one motorcyclist, and a motorcycle passenger were killed in separate crashes.
Mega Maps was provided to the NZ Herald under the Official Information Act close to a year after it was first requested and under orders from the Ombudsman.
Check the interactive graphic below to see fatal and serious crashes on NZ roads since 2000 and how current speed limits compare with the safe and appropriate speeds suggested by Mega Maps.
Interactive: Could your street be getting a speed limit reduction?
Editorial: Speed tweaks part of saving lives on roads
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
Mega Maps data
It is the first time Mega Maps has been shared outside of road controlling authorities (RCAs) such as councils and police. It has only recently been shared with the AA.
The maps, which show detail down to neighbourhood level, show the posted speed limits and also the "safe and appropriate" speeds. For the majority, that is below the posted limit.
All RCAs are required to review their speed limits under the Speed Management Guide and obliged to take into account the data contained in Mega Maps.
The reviews come after the 2017 Land Transport Setting of Speed Limits Rule replaced the 2003 Speed Limits New Zealand methodology for setting limits.
That 2003 rule applied default 50km/h limits to urban roads and 100km/h on open roads - limits which Mega Maps suggests are unsafe in most cases.
The Herald has reproduced the data on posted speed limits and safe and appropriate speeds but there is much more contained in the maps available to RCAs.
Mega Maps also shows which roads would benefit from upgrades such as engineering changes, median barriers and rumble strips to make them safer.
Associate Transport Minister Julie Anne Genter said the rate of deaths and serious injuries on the roads had been increasing over the past five years.
"Those aren't concentrated in just a few places. In fact, the majority of fatalities occur on rural roads – some are state highways and some are local roads.
"In order to reduce deaths and serious injuries we have to use evidence-based improvements to make the roads safer across a huge number of kilometres across the country," Genter said.
"We've identified the regions that have the highest deaths and serious injuries. That's Auckland, Canterbury and Waikato. But there will be improvements right across the country."
The issue of roads is highly politicised.
The previous National-led Government's Roads of National Significance programme focused on seven major road projects in mainly urban centres where there were high traffic volumes.
The current Government redirected its focus elsewhere.
Genter said there was "no question" its approach would have a more significant impact on reducing deaths and serious injuries than the Roads of National Significance.
"Roads of national significance only delivered improvements to a few stretches of road in New Zealand and they ended up reducing the amount of money that was being spent on maintenance and on low-cost, easy-to-implement improvements," she said.
'We need to hit speed hard'
NZTA's acting director of safety and environment, Niclas Johansson, said New Zealand was a long way behind in addressing trauma on the roads.
"As a New Zealander you're two to three times more likely to be killed or seriously injured on the roads [in relation to comparable countries].
"We've got a low starting point but we've got a really good opportunity in front of us to really hit that hard," Johansson told the Herald.
"We've got a big problem - speed is one component but it's a really important one. Around 25 per cent of crash statistics has a speed component. It's a really big contributing factor to the likelihood of having a crash but it also obviously impacts the severity of the crash."
Johansson said the purpose of the programme was to get better alignment with the posted speed limit and the safe and appropriate speed.
"Just because nothing has happened on a stretch of road in five years does not mean it's not going to happen tomorrow."
He pointed out that there was very little to be gained timewise by speeding.
"You can double your chances of walking away from an accident by lowering your speed by 10 per cent but what does that actually mean for the time for your trip?
"That might be something in the order of 30 seconds to 90 seconds, depending on distance. They offer very small numbers for the sake of putting yourself and your family at a much greater risk."
Johansson said Mega Maps was an important tool for RCAs to use when reviewing speed limits but not the only one.
"It isn't necessarily the right answer but it applies a national consistency to a safe and appropriate speed that will then have a local assessment including some other factors that NZTA may not have," he said.
The Setting of Speed Limits Rule required the NZTA to provide information on safe and appropriate speeds on all roads to RCAs.
Reducing speed one part of the equation
The NZTA developed the Mega Maps speed management tool specifically for RCAs as one tool to help with the process of determining the most appropriate speed limit for a certain section of road.
"It's important to recognise that use of the Mega Maps tool is only one part of a larger process which RCAs use when assessing roads and setting speed limits. The information provided by Mega Maps is a starting point, not an end point," Johansson said.
It is estimated that across 37 councils, the number of deaths and serious-injury crashes could be reduced by more than 160 a year through a combination of speed-limit changes and safety improvements.
In December last year, Transport Minister Phil Twyford and Genter announced a $1.4 billion, three-year Safe Networks Programme to make New Zealand's highest-risk roads safer.
It is that programme that is providing the funding for implementing the Speed Management Guide and safety improvements.
The improvements include features such as median and side barriers, rumble strips and shoulder-widening.
Johansson said those safety improvements were an important part of the plan.
"Not all of it is the lowering of speed, some of it is the function of the road. In some instances we will have to engineer up to maintain a strategic function of the network.
"If you look at speed only, you miss the point of maybe looking at the function of the road and what we need to provide in that context."
Genter said the Government wanted to be more ambitious in the rollout of the Speed Management Guide, which was developed under the previous Government.
"They were looking at addressing the top 10 per cent most dangerous roads over 10 years. We've said, 'let's try doing it in three because we have too many people dying on our roads'."
Genter will be signing off on a "new, ambitious" road-safety strategy and action plan later this year that will go further, but gave no further details.
"I'm very confident that the approach we're taking is evidence-based and will have a meaningful impact over time," she said.
What is Mega Maps?
Mega Maps is the name given to the Safer Journeys Risk Assessment Tool.
It is an online interactive map packed with data about the New Zealand road network gathered over years and from a number of sources.
It provides road-controlling authorities such as councils and the NZTA with a common source of base information to help develop speed management plans.
The desktop analysis is considered with local knowledge and input before decisions are made on proposed changes to speed limits.
Different layers show the network, the posted speed limits, and the mean traffic speed on urban, rural and state highway networks.
The primary layers of Mega Maps, used to calculate safe and appropriate speeds for each road, are:
• The One Road Network Classification of each road, based on its use by traffic such as an arterial route or an access road.
• Historic crash data, estimated deaths and serious injuries per kilometre and the personal risk to individual motorists.
• An automated infrastructure risk rating based on factors including the land use around the road, its roadside hazards, the nature of the road itself, the density of access and intersections, traffic volume and the lane and shoulder width.
Supplementary layers include high-risk intersections, high-risk motorcycle routes and stretches of road with high-risk curves.
Mega Maps also shows the location of the country's schools and speed cameras and shows territorial local authority, regional council and police boundaries.
• Thanks to Core Logic for road location data.