❓ This WA parliamentary question seeks clarification on the methodology used to determine road speed limits, specifically asking about exceptions to the standard process. The answer details the factors considered and the exceptions where the 85th percentile speed is not the primary determinant.
AnsweredQoN 2425Legislative Assembly
QuestionView source ↗
(a) if so, with what exceptions; and
(b) if not, what is the methodology used to determine road speed limits?
(b) if not, what is the methodology used to determine road speed limits?
AnswerView source ↗
Answered
14 August 2007
Responded by
Minister for Planning and Infrastructure
Response time
62 days
(a) Main Roads Western Australia developed their speed zoning policy and guidelines based on Australian Standards, and best practices from the eastern states and overseas.
There are a number of factors considered when determining road speed limits such as road hierarchy, function within the immediate road network system, crash history, geometry, abutting roadside development, and existing vehicle speeds which includes the 85
th
percentile speed data. Studies have shown that the 85
th
percentile speed represents the operating speed of the road as determined by the large majority of drivers.
It has been demonstrated that the 85
th
percentile speed is the safest operating speed because there is less variation in vehicle speeds and therefore less need for overtaking manoeuvres. Therefore, Main Roads supports the use of the 85
th
percentile speeds as one factor when determining road speed limits.
(b) Exceptions exist where the 85
th
percentile speed is not considered when setting speed limits. This is usually when the road or adjacent land use conditions require a lower speed limit for safety reasons. Such cases include residential streets, school zones, shared zones, heavy vehicle speed zones, speed buffer zones, on approaches to traffic signalised and roundabout controlled intersections, and on approaches to one lane bridges. These situations are considered in isolation and their speed limits have been pre-determined and implemented via speed zoning policy.
Notice: This document is created or edited using unregistered or evaluation copy of rtLib valid for testing or development purposes only. To use it for productive or any other purposes please register it. You may purchase the license on
http://www.rtlib.com
There are a number of factors considered when determining road speed limits such as road hierarchy, function within the immediate road network system, crash history, geometry, abutting roadside development, and existing vehicle speeds which includes the 85
th
percentile speed data. Studies have shown that the 85
th
percentile speed represents the operating speed of the road as determined by the large majority of drivers.
It has been demonstrated that the 85
th
percentile speed is the safest operating speed because there is less variation in vehicle speeds and therefore less need for overtaking manoeuvres. Therefore, Main Roads supports the use of the 85
th
percentile speeds as one factor when determining road speed limits.
(b) Exceptions exist where the 85
th
percentile speed is not considered when setting speed limits. This is usually when the road or adjacent land use conditions require a lower speed limit for safety reasons. Such cases include residential streets, school zones, shared zones, heavy vehicle speed zones, speed buffer zones, on approaches to traffic signalised and roundabout controlled intersections, and on approaches to one lane bridges. These situations are considered in isolation and their speed limits have been pre-determined and implemented via speed zoning policy.
Notice: This document is created or edited using unregistered or evaluation copy of rtLib valid for testing or development purposes only. To use it for productive or any other purposes please register it. You may purchase the license on
http://www.rtlib.com
Explore WA Government Data
Search the full archive in the free dashboard, or query programmatically via API.
Explore more
Government Gazette
Appointments, regulatory notices, planning changes.
Hansard
Debates, questions, speeches and sentiment.
Tabled Papers
Reports and documents tabled in Parliament.
Committees
Committee profiles and recent reports.
Regulations
Subsidiary legislation with filters and summaries.
Bills
Proposed laws and parliamentary progress.
Acts
Current WA legislation and summaries.
Explanatory Memoranda
Bills with EMs (text/PDF) available.
Members
MP profiles, party breakdown and rankings.
Pollie Rankings
Data-driven rankings across 19 categories.
Amendment Chains
Track how schemes and regulations evolve over time.