This page contains information on how the speed survey is undertaken and how it provides a measure of safety on New Zealand roads.

Background to the Annual Speed Surveys

The speed surveys are designed to monitor changes in free speeds of vehicles in both 100km/h speed limit areas and main urban 50km/h areas. Free speeds are speeds attained when the vehicle is unimpeded by the presence of other vehicles (that is, there is some distance between a vehicle travelling at a free speed and the vehicle in front of it) or by environmental features such as traffic lights, intersections, hills, corners or road works. By monitoring the speeds of unimpeded vehicles this survey measures driver choice of speed. This measure provides us with information on the effectiveness of speed management measures and provides valuable information for developing safety policies.

Speed surveys are conducted annually at sites around New Zealand to provide an estimate of the national speed profile. The speed survey results can also be broken down to a regional level and into light and heavy vehicles.

The regional surveys are designed to track changes over time in driver speed choice within regions; they are not designed to provide valid comparisons between regions. To obtain valid comparisons between regions the set of sites used in each region would need to be comparable in every way.

Surveys are carried out at about 65 open road and 65 urban sites. The sites were randomly selected in 1995 and, with only minor changes, the same sites have been surveyed each year since.

Vehicle speeds are measured by a surveyor, who surveys the site at the same time of day and day of the week as in previous years. The surveys are carried out in an unobtrusive manner to ensure that the speeds measured are minimally affected by the survey procedures.

The national speed profile provides a measure of safety on New Zealand’s roads. Research has shown a clear link between vehicle speeds and road crashes. This is because as speed increases, the stopping distance increases, there is greater probability of exceeding the critical speed on a bend, and there is greater chance other road users will misjudge how fast the speeding driver is travelling. Furthermore the severity of injuries resulting from a crash is directly related to the pre-crash speed of the vehicle, whether or not speeding was a factor in the crash.

Speed Survey results - sections