This page relates to the 2018-21 National Land Transport Programme.
Risks change over time, and up to date trends should be monitored to ensure safety programmes are addressing the biggest risks.
There are three methods for estimating road safety risk:
Waka Kotahi NZ Transport Agency’s Safer Journeys Risk Assessment Tool(external link) or the KiwiRap Road Safety Risk(external link) website are useful starting points for screening corridors, intersections or routes that may satisfy the safety risk criteria.
Please note that the risk ratings presented on these websites may not correlate exactly with the criteria, and may be based on a different crash period.
The number of injury crashes that have occurred in the last 5- or 10-year interval is determined using relevant data from the Crash Analysis System (CAS).
By using all injury crashes instead of just fatal and serious crashes to predict the number of DSI likely to occur in future, the number of crashes analysed increases, and the impact of individual high severity or low severity crashes are normalised.
For assessments completed after 31 March each year, include crash data from the previous calendar year in the analysis. See 'Calculating DSI casualty equivalents' for approved methods for calculating estimated DSI casualty equivalents.
Note:
If a corridor or intersection has a high or medium-to-high collective safety risk, it becomes a high overall safety risk for the purposes of results alignment.
If a corridor or intersection has a medium or low-to-medium collective safety risk, you can calculate personal safety risk using either injury crash data or infrastructure risk rating(external link):
- The personal safety risk calculation requires information on corridor or intersection traffic volumes. If these calculations determine that the corridor or intersection has a high or medium-to-high personal safety risk, then it becomes a high overall safety risk for the purposes of results alignment.
- The infrastructure risk rating (IRR) is shown on the Waka Kotahi Safer Journeys Risk Assessment Tool(external link). To calculate IRR, you need eight additional variables. The information required to populate these eight variables is available through Google Street View and aerial imagery or can be manually calculated from site inspections and measurements. Once the IRR is determined, you can calculate a high, medium or low overall safety risk (as set out below).
Please use the information below to calculate safety risk and to determine whether the overall safety risk is high, medium or low for the purposes of results alignment.
CloseThere are two methods for identifying safety risk to determine the results alignment of corridor and intersection improvement proposals.
The methods of calculating safety risk set out below involve using death and serious injury (DSI) casualty equivalents (see 'Calculating DSI casualty equivalents' further below).
To achieve a very high results alignment, the activities or interventions should:
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You can assess a corridor as a high overall safety risk using one or more of the following methods.
High overall safety risk for corridors is where:
Note: For road sections with an annual average daily traffic of less than 1,500 vehicles per day, you may use 10 years of crash data instead of five to increase the size of the crash sample. Where 10 years of crash data are used, the minimum number of injury crashes increases from three to five.
Figure 1: Urban (≤70km/h) corridor with estimated DSI casualty equivalents for collective risk thresholds. This is based on estimated DSI casualty equivalents per kilometre per year.
Figure 2: Rural (≥80km/h) corridor with estimated DSI casualty equivalents for collective risk thresholds. This is based on estimated DSI casualty equivalents per kilometre per year.
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A high overall safety risk for intersections is where:
Any intersection, corridor or route that does not satisfy any of the high or medium safety risk definitions is classified as low safety risk.
CloseDSI casualty equivalents are an estimation of the number of deaths and serious injuries likely to occur at an intersection or on a corridor based on the total number of injury crashes that have occurred.
There are four approved methods for calculating estimated DSI casualty equivalents for the purpose of safety risk assessment (see below).
Note:
A spreadsheet has been developed to assist practitioners calculate collective and personal risk profiles for intersections (method 1) and corridors (method 2). The spreadsheet includes an infrastructure risk rating (IRR) calculation model.
Download the ‘Determining safety risk practitioners spreadsheet’. [XLSX, 30 KB]
A simplified method may be used by multiplying each injury crash by the corresponding DSi severity factor in table 1.
Table 1: Generic corridor DSI severity indices
Speed limit |
DSI severity factor |
|
Motorised road users |
Pedestrians and cyclists |
|
≤ 50km/h |
0.16 |
0.24 |
60–70km/h |
0.23 |
0.35 |
80–100km/h |
0.34 |
0.51 |
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Use the Urban KiwiRAP(external link) method of classifying crashes at mid-blocks, and multiplying each injury crash by the corresponding DSI severity index (table 2). This index covers primary crash movement type, speed environment and midblock form.
Table 2: Corridor severity indices (source: Urban KiwiRAP(external link))
Primary crash type |
Corridor type |
|||
≤70km/h |
≤70km/h multilane |
≥80km/h |
≥80km/h |
|
A |
0.30 |
0.24 |
0.48 |
0.18 |
B |
0.37 |
0.49 |
0.82 |
0.98 |
C |
0.26 |
0.30 |
0.29 |
0.17 |
D |
0.28 |
0.23 |
0.33 |
0.26 |
E |
0.15 |
0.17 |
0.26 |
0.18 |
F |
0.05 |
0.06 |
0.15 |
0.05 |
G |
0.11 |
0.13 |
0.30 |
0.28 |
H |
0.19 |
0.10 |
0.43 |
0.43 |
J |
0.13 |
0.06 |
0.38 |
0.38 |
K |
0.18 |
0.02 |
0.22 |
0.18 |
L |
0.21 |
0.14 |
0.28 |
0.29 |
M |
0.15 |
0.14 |
0.32 |
0.69 |
N |
0.27 |
0.31 |
0.62 |
0.62 |
P |
0.27 |
0.34 |
0.66 |
0.69 |
Q |
0.49 |
0.48 |
0.43 |
0.17 |
Use the method described in the High-risk intersections guide. Tabls 3 and 4 contain severity indices for different intersection forms and controls for urban (speed limit ≤70km/h) and rural (speed limit ≥80km/h) speed environments respectively.
Table 3: Urban (≤ 70km/h) intersection severity indices (source: High-risk intersections guide)
Primary crash type |
Intersection type |
||||
Roundabout |
Traffic signals crossroads |
Traffic signals T-intersection |
Priority controlled crossroads |
Priority controlled T-intersection |
|
A |
0.10 |
0.11 |
0.11 |
0.25 |
0.25 |
B |
0.16 |
0.12 |
0.12 |
0.25 |
0.21 |
C |
0.27 |
0.18 |
0.18 |
0.19 |
0.25 |
D |
0.20 |
0.17 |
0.17 |
0.21 |
0.24 |
E |
0.11 |
0.13 |
0.11 |
0.11 |
0.10 |
F |
0.05 |
0.06 |
0.06 |
0.08 |
0.07 |
G |
0.13 |
0.10 |
0.07 |
0.20 |
0.11 |
H |
0.15 |
0.19 |
0.10 |
0.17 |
0.18 |
J |
0.15 |
0.10 |
0.10 |
0.16 |
0.15 |
K |
0.10 |
0.15 |
0.10 |
0.13 |
0.13 |
L |
0.15 |
0.15 |
0.18 |
0.18 |
0.18 |
M |
0.09 |
0.19 |
0.19 |
0.19 |
0.14 |
N |
0.23 |
0.23 |
0.24 |
0.22 |
0.24 |
P |
0.22 |
0.31 |
0.31 |
0.31 |
0.31 |
Q |
0.25 |
0.25 |
0.25 |
0.25 |
0.25 |
Table 4: Rural (≥80km/h) intersection severity indices (source: High-risk intersections guide)
Primary crash type |
Intersection type |
||||
Roundabout |
Traffic signals crossroads |
Traffic signals T-intersection |
Priority controlled crossroads |
Priority controlled T-intersection |
|
A |
0.10 |
0.22 |
0.22 |
0.40 |
0.38 |
B |
0.16 |
0.40 |
0.40 |
0.70 |
0.61 |
C |
0.27 |
0.30 |
0.30 |
0.30 |
0.36 |
D |
0.25 |
0.30 |
0.26 |
0.30 |
0.34 |
E |
0.11 |
0.19 |
0.15 |
0.33 |
0.33 |
F |
0.06 |
0.09 |
0.08 |
0.10 |
0.10 |
G |
0.13 |
0.14 |
0.11 |
0.25 |
0.41 |
H |
0.16 |
0.27 |
0.11 |
0.50 |
0.37 |
J |
0.16 |
0.20 |
0.13 |
0.36 |
0.37 |
K |
0.11 |
0.23 |
0.11 |
0.25 |
0.32 |
L |
0.19 |
0.18 |
0.11 |
0.35 |
0.40 |
M |
0.11 |
0.23 |
0.27 |
0.30 |
0.30 |
N |
0.30 |
0.60 |
0.60 |
0.60 |
0.60 |
P |
0.30 |
0.60 |
0.60 |
0.60 |
0.60 |
Q |
0.25 |
0.50 |
0.50 |
0.50 |
0.50
|
Use the method described in Safer Journeys for motorcycling on New Zealand roads guide.
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