Safe speed for environment overview
Summary of indicator
To determine the safe and appropriate speed limit and supporting infrastructure for the road and surrounding land uses to deliver safe and comfortable environments for all users.
Speeding is the biggest single behavioural factor involved in road deaths, contributing to around 40% of road fatalities each year in NSW. Speed limits are one of the simplest and most proven strategies for controlling and regulating driving speeds. Road user behaviour, including the perception of an appropriate speed of travel, can be influenced by the design and function of a road. Where possible, the speed limit of a road should be self-explaining.
This indicator will support practitioners to understand whether the posted speed limit is safe and appropriate for the road and roadside environment, and whether the road should be nominated to TfNSW for a Speed Zone Review to be conducted (see notes). Based on the outcome of the assessment, practitioners can identify the safe and appropriate posted speed and compare it to the 85th percentile speed measurement, which will determine if additional supporting infrastructure and traffic calming measures are needed to achieve the desired travel speed outcome.
Practitioners can use the appropriate speed for the environment metric to determine whether a change in posted speed limit may need to be considered based on the surrounding context/activity.
Practitioners can use the 85th percentile speed metric to measure the speed at or below which 85% of vehicles are observed to travel under conditions past a nominated point at a certain time of day.
The use of 85th percentile speed is becoming outdated and has been discontinued by many road authorities as a key factor in speed limit setting. It is not supported by the Safe System approach to road safety. The NSW Speed Zoning Guidelines should be used to identify the safe and appropriate speed limit and the use of the 85th percentile speed used solely to assess the amount of supporting infrastructure required to support that speed limit.
Metrics in detail