How is data collected?
The KiwiRAP Star Ratings are the result of a thorough visual inspection of New Zealand's roads and road design elements.
Using a vehicle specially equipped with five cameras, digital images of New Zealand's roads were recorded at 100-metre intervals. Each of the five cameras – a forward camera, rear camera, left camera, right camera and pavement camera – were aligned to film views of the road and its surrounding environment.
Digital images were then streamed together to form a video of the road. Skilled analysts inspected the footage by taking a 'virtual' drive-through of the road network. This virtual testing was completed at highway speed or on a frame-by-frame basis, depending on the complexity of the road.
The software used by the analysts enabled accurate measurement of elements such as lane widths, and the distance between the road edge and fixed hazards such as trees and power poles.
For divided roads, each carriageway was rated separately. The rated data was supplemented with several other model data sets (horizontal alignment, sight distance, overtaking opportunities, speed environment and terrain) obtained automatically off-line from New Zealand speed data sets calculated at 10-metre intervals.
Importing the resulting composite data into the KiwiRAP software for analysis, calculations were then made of the Road Protection Score (RPS) over 100-metres and Star Ratings over five-kilometre segments.
Which road elements are inspected?
Extensive research has highlighted the design elements most likely to influence the occurrence of road crashes – and the severity of those incidents.
The Star Rating approach focuses on the elements influencing the three most common and severe types of crashes on New Zealand's rural state highways.
- Run-off road crashes (which account for over 50% of all crashes)
- Head-on crashes
- Crashes at intersections
Together, these three crash types account for over 80% of all fatal and serious injury crashes on our rural roads.
The Star Rating system looks at not just the design and engineering elements of the road itself, but also any intersecting road that meets with it. Road elements can include:
- Road section type (motorway, 4-lane divided, 2-lane undivided, etc)
- Lane width
- Sealed shoulder
- Horizontal alignment*
- Terrain*
- Delineation
- Overtaking provision
- Overtaking requirements*
- Speed environment*
- Offset and severity of roadside hazards
- Traffic volume
KiwiRAP Star Rating tool
Midblock Form
This midblock form enables analysts to categorise road section attributes including:
- Whether it is divided or undivided
- Lane width
- Width of sealed shoulders
- Speed limit
- Delineation – and more
Intersection Form
The intersection form enables intersections to be individually assessed, breaking down features – such as signage, railway crossings, street lighting – that may be found at an intersection.
Intersection elements:
- Intersection type (grade separated, 3-leg, T-junction etc)
- Volume of traffic on side road*
- Alignment of legs
- Sight distance
- Right turn provision
- Left turn provision
- Speed environment (of through road).
*These elements have been measured using NZ Transport Agency database information, rather than information sourced from the video.