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The NZ Transport Agency's risk assessment tool, Mega Maps, suggests only a small fraction of the state highway network in the South should have a 100kmh speed limit.
Information about road width, hazards and alignment are used to determine a safe and appropriate travel speed.
The Mega Maps data was provided to The New Zealand Herald under the Official Information Act close to a year after it was first requested and under orders from the Ombudsman.
Nationally, the tool estimates 95% of open roads should have a speed limit lower than 100kmh, and that figure is higher in Otago and Southland.
It also suggests a lower speed limit for some of the accident hot spots in the South, including a 60kmh limit for the Crown Range Rd, 80kmh for the Te Anau-Mossburn highway, 80kmh for the Kawarau Gorge (State Highway 6) and 80kmh on Main South Rd (SH1), south of Mosgiel.
A 30kmh and 40kmh top speed for most urban areas is also recommended.
Information from the maps is used by both the agency and local councils when deciding on new speed limits.
Police and the Automobile Association also have access to the information.
An agency spokesman said the Mega Maps tool had been used for the past two years and had helped with decisions on lower speed limits both on state highways and local roads.
As work was still being completed, the details of any speed limit changes on state highways were not able to be provided, the spokesman said.
MegaMaps was only one part of a larger process which councils and the agency followed when assessing roads and setting speed limits.
AA Otago District Council chairman Malcolm Budd said the association was against any blanket reduction and instead supported targeting those roads which posed the most risk to motorists.
``We agree some roads should be reduced to 40kmh or 80kmh but they've got to be roads of high risk and have safety benefits.''
The Crown Range Rd was a good example of a road where multiple speed limits should be introduced, Mr Budd said. - Additional reporting NZME