Speed limits (Completed)

The AA Research Foundation commissioned researchers from Waikato University to analyse before-and-after speeds on a range of state highways that had limit reductions in 2020 or 2021. The project also did simulator testing of people’s driving on higher-speed and urban roads that had had limits lowered.

With speed reductions being a key tool being used to improve road safety in New Zealand this research investigated:

  • What proportion of drivers comply with lower limits?
  • How long does it take drivers to adapt to a limit change?
  • What road characteristics lead to better adaptation to limit changes?
  • What views do drivers have about limit changes?


Adaptation to speed limit changes 

Key findings - real-world before-and-after speeds

  • There was generally a speed reduction when limits were lowered – and it happened quickly (where it happened)
  • There was significant variability between locations. Some sites had a small reduction, some a bigger reduction while a few sites had no change or even speed increases.
  • Road geometry was found to have some affect on speed choice but not explain all the variability. The researchers believe habit and established norms from past experience were at least as important.
  • A large proportion of drivers were travelling above the new speed limits – by a significant amount in some locations.
Average speeds seven weeks after limit dropped to 80km/h
At or below 80km/h 33% of locations
81-83km/h 27% of locations
84-86 km/h 23% of locations
87km/h+ 17% of locations


Key findings – simulator section

  • Drivers were more likely to travel above the limit on unfamiliar roads.
  • Drivers had poor recollection of the speed limits on roads they had recently travelled on (even if they went past a speed sign) and poor recollection of what speed they had been driving at.
  • There were mixed views on whether the lower limits were supported but widespread agreement that they were safer.
  • Speed signs made some difference in lowering speeds when encountered and the majority of participants felt more signage or road markings would help adaptation to speed changes.
  • Most participants viewed the speed limit as the target authorities wanted them to drive close to, and the majority felt negatively towards people driving slower or faster than the limit.

Previous related research

The AA Research Foundation has worked with Waikato University's Transport Research Group previously on several projects looking into aspects of driver risk awareness.

Page last updated: September 2023

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