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InfrastructureRiskRating(IRR)Manual
PreparedfortheNewZealandTransportAgency
July2016
Infrastructure Risk Rating Manual
i
DevelopmentStatusoftheIRRModel
The Infrastructure Risk Rating (IRR) model and methodology presented in this document has been
developed, trialled and refined in a number of New Zealand locations. The working group tasked
with developing the model are satisfied that the results being generated by the IRR model are
intuitive and fit for purpose. However, it should be noted that further development and revision may
occur in the future.
Disclaimer
This document has been prepared for the benefit of the NZ Transport Agency. No liability is accepted
by the company’s or persons who have prepared this document with respect to its use by any other
person.
This disclaimer shall apply notwithstanding that this document may be made available to other
persons for an application for permission or approval to fulfil a legal requirement.
Acknowledgments
The IRR model has been developed as part of a collaborative process. The working group tasked with
the development and testing of the model are:
Colin Brodie & Fergus Tate, New Zealand Transport Agency, Wellington Paul Durdin & Haris Zia, Abley Transportation, Christchurch Shane Turner, MWH, Christchurch Gina Waibl, Gina Waibl Consulting, Christchurch
Infrastructure Risk Rating Manual
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Contents
Development Status of the IRR Model .................................................................................................... i
Disclaimer................................................................................................................................................. i
Acknowledgments .................................................................................................................................... i
1 Introduction .................................................................................................................................... 1
1.1 Infrastructure Risk Rating Features ........................................................................................ 1
2 Infrastructure Risk Rating Coding ................................................................................................... 2
2.1 Definition of a Divided Road ................................................................................................... 2
2.2 Identifying Sections for Coding ............................................................................................... 3
2.3 Data Fields ............................................................................................................................... 4
2.4 Road Stereotype ..................................................................................................................... 6
2.5 Alignment ................................................................................................................................ 6
2.6 Carriageway Width .................................................................................................................. 7
2.7 Roadside Hazards .................................................................................................................... 8
2.8 Land Use ................................................................................................................................ 11
2.9 Intersection and Access Density ........................................................................................... 12
2.10 Traffic Volume ....................................................................................................................... 13
3 IRR Model ...................................................................................................................................... 14
4 Automated Process Overview ....................................................................................................... 18
4.1 Geospatial Process for Creating Homogenous Sections ....................................................... 18
4.2 IRR Attributes Coding Automation ........................................................................................ 19
4.2.1 Road Stereotype Coding Automation ........................................................................... 19
4.2.2 Alignment Coding Automation ..................................................................................... 19
4.2.3 Carriageway Width Coding Automation ....................................................................... 19
4.2.4 Roadside Hazard Risk Coding Automation .................................................................... 19
4.2.5 Land Use Coding Automation ....................................................................................... 20
4.2.6 Intersection Density Coding Automation ...................................................................... 20
4.2.7 Access Density Coding Automation .............................................................................. 20
4.2.8 Traffic Volume Coding Automation .............................................................................. 21
Appendix A: Roadside Hazard Rating Examples ................................................................................... 22
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1 Introduction Infrastructure Risk Rating (IRR) is a road assessment methodology designed to assess road safety
risk, primarily as an input to the speed management process. The road safety risk is assessed by
coding each road and roadside feature that feeds into the IRR model so that a risk rating can be
determined.
This Appendix describes the IRR model and the methods available for applying it. The Speed
Management Guide provides information on how IRR is used.
1.1 InfrastructureRiskRatingFeatures In IRR, eight key features have been identified that impact on safety risk. These are:
Road stereotype
Alignment
Carriageway width
Roadside hazards
Land use
Intersection density
Access density
Traffic volume
Section 2 of this Appendix provides guidance for coders to identify sections for coding and to select
the appropriate category for each feature rated in IRR. Section 3 includes the risk scores associated
with each IRR feature and the form of the IRR model. There is also a separate IRR spreadsheet tool
available which can be used to calculate the IRR Score.
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2 InfrastructureRiskRatingCoding To assess risk and determine an Infrastructure Risk Rating (IRR) score, the IRR features must be
assessed and coded by assigning each feature a value based on the available categories (as shown in
Sections 2.4 to 2.10). However, before coding can begin, road sections need to be identified for
coding as outlined in Sections 2.1 and 2.2 below; and section location and description data entered,
as shown in Section 2.3. Coding and sectioning can either be done manually or using an automated
process (see Section 4).
Various media and data sources will be available to the coder. Aerial imagery is useful for gaining an
overview of the section to be coded and can be used to code features such as alignment. Existing
data sources, such as Road Asset Maintenance Management (RAMM) databases, are useful for
coding traffic volume and can be used to code other features such as carriageway width. However,
for some features, particularly roadside hazards, a street level view is required. If high speed video is
available this is ideal, but otherwise coding of these features can be done during a site visit. Coding
can also be done using still images, such as Google Street View, but this will likely be slower and less
accurate as it is more difficult to get a complete picture of the road corridor.
As with other risk rating methodologies, divided and undivided carriageways are coded differently.
Divided carriageways are coded in both directions, while undivided carriageways are coded once,
with both sides of the road coded while viewing the road travelling in one direction.
An IRR spreadsheet tool has been developed as an accompaniment to this coding manual, and can
be used for the input of coding data and calculation of the IRR Score.
2.1 DefinitionofaDividedRoad For the purposes of coding, a road is treated as divided if there is a physical feature separating
opposing traffic flows and preventing vehicle movements across the median. A physical separating
feature is any kind of raised median, such as a kerb island, or safety barrier. There may be gaps
present in the median at intersections.
Divided roads include traversable and non‐traversable medians. A divided traversable median may
not stop an out of control vehicle from crossing the median but is sufficient to deter or prevent
general vehicle turning movements across the median.
If there are flexi‐posts present in the median, the road would be coded as divided if the posts are
spaced closely enough to prevent vehicle movements across the median.
Roads with features such as a flush median, centreline rumbles strips or wide centrelines do not
prevent vehicle movements across them and as such should be coded as undivided.
Short lengths of divided road (less than 1km), such as on the approach to an intersection are ignored
and treated as part of the undivided road section and vice versa for divided roads with short sections
of undivided road.
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2.2 IdentifyingSectionsforCoding To simplify and expedite coding, road sections are selected where there is little variation in IRR
features. These are referred to as homogenous sections. One way to think of these is that, broadly,
homogenous sections are those where the speed limit would be the same.
To select homogenous sections prior to coding:
1. Aim for sections to be around 5km in length, though sections between 3km and 7km in length
are acceptable. Shorter lengths (around 1km) can be used where necessary but should be
avoided where possible. These shorter lengths are typically only expected where there has been
a significant change in road stereotype or land use, intersection density or access density.
2. Consider land use and intersection and access density and make section breaks where land use
changes or intersection and access density change significantly. If the change is over a short
length (<1km) then consider how significant the change is and whether a section break is
required. If there is a speed limit change in the vicinity of the land use change (within 500m)
then the section should start/end at the speed limit change. Where multiple speed limits are
present, create section boundaries at the urban/rural boundary (where urban and rural are
defined by land use as shown in Section 3). Maps and aerial photography can be used to assist
with this prior to coding although a street level view is recommended to define the section
boundaries.
3. Road stereotype must be unchanged over the length, except for short changes <1km in length
such as at intersections, turning bays, slow vehicle bays, short passing lanes etc. Use maps and
aerial photography prior to coding if desired, and refine using a street level view as not all road
stereotype changes will be identified from maps.
4. For rural roads use aerial imagery to identify changes in road alignment and create initial
homogenous sections at locations where the alignment changes. Section 2.5 gives further
information on defining alignment. Aim for consistent alignment, although changes between
two adjoining alignment categories, or large changes in alignment over short lengths (<1km), are
acceptable.
5. Ideally, the same traffic volume category should apply to the whole homogenous section.
However, small changes in traffic volume, such as when the traffic volumes fall near the
boundary of two categories are acceptable.
6. Create a separate section for each direction of a divided road e.g. divided roads should have at
least one section for each direction. However, ignore short lengths (<1km) where the road
briefly changes from undivided to divided or vice versa.
During coding some adjustment to the homogeneous sections may be required, particularly where
there is significant change in roadside hazards. Sections should be defined so that there is
consistency in the roadside hazard coding and section breaks should be used where there is a clear
change in the roadside hazards. For example, if the road changes from a flat plain with occasional
trees on either side, to a road in a valley with a steep slope on one side and a drop off on the other,
these should form two sections.
Distinct changes in carriageway width may also influence the definition of homogeneous sections.
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2.3 DataFields
In addition to coding the road attributes a number of data fields should be recorded. The data fields
that are input to the IRR spreadsheet are shown in TABLE 2‐1.
TABLE 2‐1: IRR DATA FIELDS
Data Field Description
IRR Section
Reference Number
Section reference number selected by the user. Any value can be used e.g. 1,
2, 3; A1, A2, A3 etc.
IRR Homogenous
Section Name
Name given to each homogenous section to assist with referencing e.g. Levin‐
Otaki 1, Levin‐Otaki 2, Waikanae 1, Waikanae 2, Blockhouse Bay, Ponsonby
Coder Name Full name of person undertaking coding. It is recommended that the coder’s
organisation is also included e.g. John Smith (ABC Consulting)
Coding Date The date on which coding was undertaken
Street Level Data
Source
The data source that provides a street level view used to complete the coding
e.g. state highway video, Google Street View, drive over survey
Street Level Data
Source Survey Date
The date of capture of the data source used
Local Road/State
Highway
Denotes whether the section is a state highway or local authority road
Road Name The name of the road(s) or state highway number e.g. Henderson Road, State
Highway 1, Orchard East Road/Orchard West Road. Where the state highway
has an alternative name this should be entered here, and the state highway
number entered in the next field.
State Highway
Number
The number of the state highway e.g. SH1N, SH07. Not applicable to local
roads.
Section From
RS/Intersecting Road
Reference denoting start point of the section on the road being coded. For
state highways this is the route station number e.g. RS347, RS1026. For local
roads this will usually be the name of an intersecting side road, e.g. Oxford
Street. The intersecting side road chosen must be one that has just been
passed, when viewed in the direction of travel in which the road section is
being coded.
Distance From km The distance in kilometres from the state highway route station or
intersecting side road shown in “Section From RS/Intersecting Road”.
Section From RAMM
ID
The RAMM ID that applies at the start of the section being coded e.g. 2540,
663. This field is optional.
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Data Field Description
Section To
RS/Intersecting Road
Reference denoting end point of the section on the road being coded. For
state highways this is the route station number e.g. RS347, RS1026. For local
roads this will usually be the name of an intersecting side road, e.g. Oxford
Street. The intersecting side road chosen must be one that has just been
passed when viewed in the direction of travel in which the road section is
being coded.
Distance To km The distance in kilometres from the state highway route station or
intersecting side road shown in “Section To RS/Intersecting Road”.
Section To RAMM ID The RAMM ID that applies at the end of the section being coded e.g. 2540,
663. This field is optional.
Direction The direction of travel in which the road section is being coded i.e. Increasing
(I), Decreasing (D), Both (B) for state highways or Eastbound (EBD),
Westbound (WBD), Southbound (SBD), Northbound (NBD) for local roads. This
value should be consistent with the “from” and “to” references above.
Section Length km The length of the section in kilometres. This value should be consistent with
the “from” and “to” references above.
Section Location
Description
Description of the section location e.g. Rolleston, Dunsandel‐Heslerton Road,
South of Levin, Dunedin Central, South Dunedin, Ilam.
Coding Comments A field for coders to enter any comments they wish to make, such as
assumptions made, particularly where there is uncertainty in coding a
particular feature. For example, when coding the right side hazard risk, the
coder could comment: “aggressive vertical faces/unguarded drop part of
distance, low scrub/ low severity property hazards part of distance, so coded
as High overall”.
Fatal Crash Count
(5yr)
The number of fatal crashes that have occurred on the section over the most
recent five year crash period with data available e.g. the number of fatal
crashes from 2010 to 2014 occurring on the section. This field is not required
to calculate the IRR and is therefore optional.
Serious Crash Count
(5yr)
The number of serious injury crashes that have occurred on the section over
the most recent five year crash period with data available. This field is not
required to calculate the IRR and is therefore optional.
Minor Crash Count
(5yr)
The number of minor injury crashes that have occurred on the section over
the most recent five year crash period with data available. This field is not
required to calculate the IRR and is therefore optional.
Average AADT The average length weighted Average Annual Daily Traffic volume over the
section. Use the year that corresponds to the last year of the crash data used
e.g. if crash data is 2010 to 2014 then the 2014 AADT should be entered here.
This field is not required to calculate the IRR and is therefore optional.
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2.4 RoadStereotype Road stereotype is recorded by selecting one of five categories, as shown in TABLE 2‐2 below.
TABLE 2‐2: ROAD STEREOTYPE CATEGORIES
Categories Description
Unsealed Any road that is unsealed
Two lane undivided An undivided road with one lane in each direction
Multi‐lane undivided An undivided road with more than one lane in each direction. Includes roads
with two lanes in one direction and one lane in the other direction.
Divided ‐ traversable Divided road with a traversable median
Divided – non
traversable & one way
Divided road with a non‐traversable median, and one way streets.
A divided road with a non‐traversable median is one that will stop an out of control vehicle from
crossing the median. A non‐traversable median will typically have a safety barrier present and/or
10m+ separation between opposing traffic flows.
A divided road with a traversable median is one that has features that prevent vehicle movements
across the median but will not stop an out of control vehicle from crossing the median. Traversable
medians include kerb islands, closely spaced flexi‐posts, or a separation of less than 10m between
opposing traffic flows. See Section 2.1 for a definition of divided and undivided roads.
Where there is any ambiguity or overlap between categories, the category that appears higher in the
table should be selected e.g. if a road is unsealed and one way then the unsealed category should be
selected.
Homogeneous sections are defined based, in part, on road stereotype so aside from short changes in
road stereotype e.g. at short (<1km) passing lanes, the road stereotype should be the same over the
homogeneous length.
2.5 Alignment Alignment is categorised based on the degrees of turn per km. Four categories are used, as shown in TABLE 2‐3 and these can be coded using a geospatial dataset or manually using judgement.
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TABLE 2‐3: ALIGNMENT CATEGORIES
Categories Definition Description
Tortuous ≥300 degrees of turn/km The road is tortuous with consecutive curves and
numerous sharp (with typical radii of 350m to 500m)
and very sharp curves (with typical radii <350m), and
can generally be driven at less than 75km/hr.
Winding ≥150 and <300 degrees of
turn/km
The road is winding, with many consecutive curves and
sharp curves (with typical radii of 350m to 500m), and
can generally be driven at 75km/h‐85km/h.
Curved ≥50 and <150 degrees of
turn/km
The road is curved and has moderate curves (with
typical radii 500m‐1500m) and can generally be driven
at 85km/h‐100km/h, though some straight sections or
isolated sharp curves may also be present.
Straight <50 degrees of turn/km The road is straight or gently curved (typical radii
>1500m) and can be driven at 100km/h or more.
Alignment may vary over a homogeneous length, therefore the average category should be selected. If the average value falls half way between two categories, then the higher risk category (shown highest in TABLE 2‐3) should be selected. For example, over a 5km homogeneous length, if 4km is straight or gentle, 2km curved, and 400m winding, then the alignment should be coded as “straight or gentle”. If there is 2.5km straight or gentle and 2.5km curved, then curved should be selected. Homogenous sections aim for consistent alignment, although changes between two adjoining alignment categories, or large changes in alignment over short lengths (<1km), are acceptable.
2.6 CarriagewayWidth Carriageway width risk is rated by coding both lane and sealed shoulder width as shown in TABLE 2‐4 and TABLE 2‐5. These lane and shoulder widths should be measured or taken from asset management databases
where practicable. If data is not readily available then visual judgement can be used by comparing
the lane and shoulder widths to vehicles travelling on the road (a truck is generally 2.5m wide and
cars are typically between 1.8m and 2.3m wide).
TABLE 2‐4: LANE WIDTH CATEGORIES
Proposed Lane Width Categories Description
Narrow (<3.0m) Narrow lane width <3.0m is generally present
Medium (3.0m to 3.5m) Medium lane width 3.0m to 3.5m is generally present
Wide (>3.5m) Wide lanes >3.5m are generally present
If a road has no edgeline markings for a shoulder, then the lane widths are measured from the edge of seal, since a vehicle can be considered to be able to travel to the edge of the sealed surface.
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Where there is more than one lane, only the narrowest lane width is taken into consideration. However, cycle lanes and other special vehicle lanes, such as bus lanes, should be ignored. For unsealed roads or roads with no marked centreline, the lane widths are estimated using
judgement to determine the number of lanes based on travelled vehicle paths.
Where lane width varies along the homogeneous section, coding is based on the category that generally applies over the section. TABLE 2‐5: SEALED SHOULDER WIDTH CATEGORIES
Proposed Shoulder Width Categories Description
Very narrow shoulder (0 to <0.5m) Very narrow with little or no shoulder, <0.5m, is
generally present
Narrow shoulder (0.5m to 1.0m) Noticeable but narrow shoulder, 0.5m to 1.0m, is
generally present
Wide shoulder (>1.0m to 2.0m) Good wide shoulder, >1.0m to 2.0m, is generally
present
Very wide shoulder (>2.0m) Very wide shoulder, >2.0m, is generally present
The sealed shoulder width is measured from the centre of the painted edgeline (excluding audio
tactile ribs outside the painted edgeline) to the unsealed surface. If the edge of seal begins to break
up on the shoulder, the sealed shoulder width should be measured up to where the edge break
occurs.
Roadside parking should be coded as shoulder. However, ignore cycle lanes and other special vehicle
lanes.
For divided roads the left hand shoulder width is measured.
For undivided roads the lesser (minimum) of the left and right hand shoulder width is measured. Where shoulder width varies along the homogeneous section, coding is based on the shoulder width that generally applies over the section.
2.7 RoadsideHazards Roadside Hazards is one of the most important and difficult features to code. It involves assessing
hazard risk based on both the severity of the hazard and its offset, as well as determining which code
to use to represent the homogeneous section being rated.
Roadside hazards are rated separately for each side of the road. For divided roads, when recording
hazards on the right‐hand side, record hazards as measured from the right side edge of the divided
carriageway e.g. record hazards in the median and if there are no hazards present in the median
then record the next nearest hazard TABLE 2‐6 provides guidance on how to assess roadside hazard
risk based on the offset and severity of identified hazards. Appendix A provides example photos of
each roadside hazard risk category. The roadside hazard offset is recorded from the edgeline if one is
present. If there is no edgeline, then the offset is recorded from the edge of seal.
Infrastructure Risk Rating Manual
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For a group of point hazards to receive a particular risk score they need to be at a density that the
likelihood of the hazard being hit is relatively high. Therefore TABLE 2‐6 requires that 20+ point
hazards be present per kilometre (or one every 50m on average) for the particular hazard code to
apply. Similarly, if there are intermittent continuous hazards, such as structures/buildings or regular
short sections of cliffs and slopes, then these should occur at relatively regular intervals and cover at
least 50% of the length over which they occur. For example, if a section has short sections exposed
to cliffs over >50% of the length within 5m, then this should be coded as Severe.
If the hazards in question do not meet these density requirements, then judgement is required to
determine the average hazard code. For example, if part of the section has regular short sections
(<50%) exposed to cliffs within 5m (Severe) and metal barriers within 5m present (Minor) over the
remainder of the section on one side, then this could be coded as High or Moderate. It should be
coded as High if cliffs are present for close to 50% of the section and Moderate if there is
significantly less than 50%.
In cases where the roadside hazards change regularly over short sections the average hazard code
should be selected. For example, if the section is an open plain with intermittent trees and poles
(<20/km) then the average roadside hazard code should be selected. In this case if the trees and
poles are generally between 5m and 10m from the edge of seal then the hazard coding is alternating
between Moderate (where there are trees and poles) and Negligible (where there are no hazards)
and therefore the code Minor should be selected.
Finally, as the coding is being done over homogeneous lengths some judgement may be required to
determine the roadside hazard risk code that best represents the entire homogeneous section.
However, as stated in Section 2.2, if there is a distinct change in roadside hazard a new
homogeneous section break should be created.
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TABLE 2‐6: ROADSIDE HAZARD RISK WITH HAZARD SEVERITY AND OFFSET DESCRIPTIONS
IRR
Roadside
Hazard
Risk
IRR Roadside Hazard Risk Description Example Hazards
Severe Aggressive/severe continuous hazards
and cliffs, within 5m*
OR
20+ non‐frangible point hazards per
kilometre (1+ per 50m) or rigid
structures/bridges/buildings, within
5m
Aggressive/severe continuous hazards can
include:
Aggressive vertical faces
Deep drainage ditches
Cliffs with steep or high drop offs, and/or
deep water, that would result in death
regardless of speed
Examples of non‐frangible point hazards
include:
Trees, signs, posts, poles >=10cm
diameter
Large boulders (>=20cm diameter)
Unprotected barrier ends
High Cliffs or deep water at 5m to <10m*
Roll‐over up‐slopes and downslopes
(e.g. >15⁰ and >1m high) at <5m*
Moderate Aggressive/severe and moderate
continuous hazards at 5m to <10m,
excluding cliffs and deep water*
OR
20+ non‐frangible point hazards per
kilometre (1+ per 50m) or rigid
structures/bridges/buildings at 5m to
<10m
OR
Car parking or semi‐rigid structures or
buildings at <5m*
Aggressive/severe and moderate continuous
hazards can include:
Aggressive vertical faces
Deep drainage ditches
Roll‐over up‐slopes and downslopes (e.g.
>15⁰ and >1m high)
Non‐frangible point hazards can include:
Trees, signs, posts, poles >=10cm
diameter
Large boulders (>=20cm diameter)
Unprotected barrier ends
Minor Metal and concrete safety barriers at
<5m*
Car parking or semi‐rigid structures or
buildings at 5m to <10m*
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IRR
Roadside
Hazard
Risk
IRR Roadside Hazard Risk Description Example Hazards
Low Metal and concrete safety barriers at
5m+*
Low severity property damage hazards
at any distance*
All hazards at >=10m*
Low severity property damage hazards can
include:
Kerbs
Wire‐rope barriers
Level and safe slopes (<=15⁰ and <=1m
high) with no hazards
Frangible trees, posts, poles <10cm
diameter
*over 50%+ of the length where they occur intermittently
2.8 LandUse The Land Use feature takes into account the surrounding land use. The selection of the most
appropriate code can also be informed by the presence of accessways and intersections (TABLE 2‐7).
The purpose of the land use code is to give an indication of the likely level of activity present on the
road. This includes pedestrian and cyclist activity along and across the road, as well as vehicle
movements – parking and driveway manoeuvres and vehicles turning to and from intersections and
accessways etc.
Code changes in land use where the change is present for 1km or more.
TABLE 2‐7: LAND USE
IRR Land Use &
Access
Categories
Description
Commercial strip
shopping
Characterised by numerous shops facing the streetfront with high levels of
activity, particularly pedestrians, cyclists and high occupancy on‐street parking
resulting in many vehicle movements to and from the road. Regular
intersections and accesses will also be present.
Commercial big
box/Industrial
Large (big box) shops and/or industry/factories with intermittent large
accessways and intersections leading to large car parking areas. Regular
intersections and smaller accesses are also likely to be present. Some
pedestrian and cyclist activity may be present.
Urban residential Urban residential area dominated by housing with frequent driveways and on‐
street parking. Regular intersections and accesses are present. Pedestrian and
cyclist activity is also likely to be present, particularly at certain times of the
day.
Rural towns Rural town with mixture of residential and some shops. Some intersections
and accesses are present. Some pedestrian and cyclist activity may also be
present.
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IRR Land Use &
Access
Categories
Description
Controlled access Road with roadside development and controlled access, such as an urban
state highway or arterial where there are few accesses to the road e.g. as a
result of a service road. Some pedestrian and cyclist activity may also be
present but with few crossing movements.
Rural residential Rural area with accesses present to private dwellings and farms. There may be
the occasional industry/factory present. Some pedestrian and cyclist activity
may also be present, particularly at certain times of the day, but with few
crossing movements.
Remote rural Only occasional accesses and intersections are present. Surrounding land is
rural with few houses and almost no industry.
No access No accessways or at grade intersections are present and pedestrians and
cyclists are not allowed e.g. motorway.
When coding, consider both what the adjacent land use looks like and how it is accessed from the road as the purpose of coding this feature is to capture the impact of land use on vehicle movements and the general level of activity present that impacts on the road. For example, if there are commercial big box retail shopping centres present and these are accessed from a highway from a few intermittent intersections then a judgement will need to be made as to whether this should be coded as Commercial Big Box/Industrial or Controlled Access. If there is uncertainty around which category to select then choose the category that appears higher
in the table e.g. choose commercial strip shopping over rural towns if coding a section in a rural
town that has a long length (1km+) of commercial strip shopping.
2.9 IntersectionandAccessDensity The at‐grade intersection and access density should also be recorded as shown in TABLE 2‐8 and
TABLE 2‐9.
TABLE 2‐8: AT‐GRADE INTERSECTION DENSITY
At‐Grade Intersection Density
10+ intersections / km
5 to <10 intersections / km
3 to <5 intersections / km
2 to <3 intersections / km
1 to <2 intersections / km
<1 intersection / km
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TABLE 2‐9: ACCESS DENSITY
Access Density
20+ accesses / km
10 to <20 accesses / km
5 to <10 accesses / km
2 to <5 accesses / km
1to <2 accesses / km
<1 access / km
The appropriate intersection and access density category should be selected by counting the number
of intersections and accesses and dividing by the homogenous section length to determine the
average.
Where intersection density or access density changes significantly over 1km or more, then a break
should be made in the homogenous section. Where a significant change occurs over a short length
(<1km) then judgement should be used to determine whether a section break is required, depending
on how large the change in density is.
2.10 TrafficVolume Traffic volume is coded using four broad categories based on Annual Average Daily Traffic (AADT) volumes as shown in TABLE 2‐10. TABLE 2‐10: TRAFFIC VOLUME CATEGORIES
IRR AADT Categories
<1,000 veh/day
1,000‐<6,000 veh/day
6,000‐<12,000 veh/day
12,000+ veh/day
The traffic volume should be recorded for the carriageway being coded. For undivided roads the traffic volume in both directions should be coded, and for divided roads the traffic volume on the single direction carriageway being coded should be recorded. For divided roads, if the traffic volume is not available by direction, then the two‐way traffic volume should simply be halved. Homogeneous sections should be defined so that the whole section falls into the same traffic volume category, however, small changes in traffic volume that fall outside of a traffic volume category are acceptable. Traffic volume should be coded using available count data such as that held in asset management databases.
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3 IRRModel
Infrastructure Risk Rating is a multiplicative model as shown in EQUATION 3‐1 below.
EQUATION 3‐1: IRR MODEL
10
2
Where IRR Score = <0, set IRR Score equal to 0
TABLE 3‐1 shows how the IRR Score is converted to an IRR band
TABLE 3‐1: IRR BANDS IRR Score Rural Urban
0 to <0.8 Low Low
0.8 to <1.2 Low-Medium Low
1.2 to <1.6 Medium Low
1.6 to <2.0 Medium-High Low-Medium
2.0 to <2.4 High Medium
2.4 to <2.8 High Medium-High
2.8+ High High
Rural and urban classification is based on the coded land use category. Corridors with the following
land use categories are assessed as rural corridors:
No Access
Rural Residential
Remote Rural
Urban thresholds are applied to corridors that are coded with the following land use categories:
Commercial Big Box/ Industrial
Commercial Strip Shopping
Urban Residential
Controlled Access
Rural Town
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TABLE 3‐2 to TABLE 3‐9 show the risk scores associated with each attribute for each of the eight IRR
features.
TABLE 3‐2: ROAD STEREOTYPE RISK SCORES
Road Stereotype Risk Score
Unsealed 10
Two lane undivided 3.7
Multi-lane undivided 3.4
Divided - traversable 3.0
Divided - non-traversable 1.0
One Way 1.0
TABLE 3‐3: ALIGNMENT RISK SCORES
Alignment Risk Score
Tortuous 6.0
Winding 3.5
Curved 1.8
Straight or gentle 1.0
TABLE 3‐4: CARRIAGEWAY RISK SCORES Lane Width
Shoulder Width <3.0m – Narrow 3.0m to 3.5m - Medium >3.5m – Wide
0m to <0.5m - Very Narrow 2.01 1.79 1.58
0.5m to 1.0m - Narrow 1.79 1.45 1.18
>1.0m to 2.0m - Wide 1.22 1.00 0.85
>2.0m - Very Wide 1.00 0.78 0.66
TABLE 3‐5: ROADSIDE HAZARD RISK SCORES
Roadside Hazard Risk Risk Score
Severe 2.80
High 2.28
Moderate 1.43
Minor 0.67
Low 0.40
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TABLE 3‐6: LAND USE RISK SCORES
TABLE 3‐7: AT‐GRADE INTERSECTION DENSITY RISK SCORES
At‐Grade Intersection
Density Risk Score
10+ intersections/km 5.00
5 to <10 intersections/km 2.60
3 to <5 intersections/km 1.50
2 to <3 intersections/km 1.25
1 to <2 intersections/km 1.15
<1 intersection/km 1.00
TABLE 3‐8: ACCESS DENSITY RISK SCORES
Access Density Risk Score
20+ accesses/km 1.30
10 to <20 accesses/km 1.10
5 to <10 accesses/km 1.06
2 to <5 accesses/km 1.03
1 to <2 accesses/km 1.01
<1 accesses/km 1.00
Land Use Risk Score
Commercial strip shopping 5.00
Commercial big box/Industrial 4.00
Urban residential 3.00
Rural towns 2.50
Controlled access 2.00
Rural residential 1.50
Remote rural 1.00
No access 1.00
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TABLE 3‐9: TRAFFIC VOLUME RISK SCORES
Traffic Volume Risk Score
<1,000 veh/day 1.00
1,000-<6,000 veh/day 1.40
6,000-<12,000 veh/day 2.20
12,000+ veh/day 3.00
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4 AutomatedProcessOverview A geospatial process has been developed to expedite IRR coding so that it can be widely applied in a
cost effective manner. While this process has some limitations and is likely to be less accurate than
manual coding for some attributes, it does have the benefit of providing an objective network‐wide
assessment that eliminates inconsistencies between coders undertaking a manual assessment.
Results from testing the automation process are promising; achieving an R2 value of 0.92 for
approximately 134km of Top of the South region network. Of the 51 sections trialled, 84% fell within
the same IRR band and only one section1 fell more than one band away from the band determined
from manual coding.
4.1 GeospatialProcessforCreatingHomogenousSections The geospatial process developed for creating homogenous sections is outlined in FIGURE 1 below.
As per the Speed Management Framework, the primary factor in determining a safe and appropriate
speed is the surrounding land use. Corridors with a uniform land use are then segmented further
based on changes in IRR attributes that contribute significantly to the IRR Score. Each step of the
process incorporates thresholds developed to avoid segmenting corridors due to short changes in
road attributes such as overtaking lanes or intersection approach medians.
FIGURE 1 IRR AUTOMATED SEGMENTATION PROCESS
1 This has since been further improved through refining the automated corridor segmentation process that was originally trialled.
Segmentation Thresholds:
Urban: 250m, Rural: 500m
Urban & Rural: 1km
Rural: 1km
Urban & Rural: 1km
IRR Homogenous Corridors
4th Segmentation: Traffic Volume
3rd Segmentation: Alignment (Rural only)
2nd Segmentation: Road Stereotype
1st Segmentation: Land Use
Centreline Aggregated by Posted Speed Limit & Road Name
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4.2 IRRAttributesCodingAutomation The coding of each IRR feature has been automated. For some features, existing geospatial data is
used, while for others, approximations are made based on the value of other IRR features. Where a
feature’s value has been approximated, these values must be manually checked and updated when a
section is identified for speed management review.
4.2.1 RoadStereotypeCodingAutomation The coding of road stereotype has been automated by drawing from the Road Asset Maintenance
Management (RAMM) database. The RAMM database includes number of lanes, divided/undivided
and whether the road is sealed or unsealed. All divided roads with a median barrier are assumed to
be non‐traversable, and divided roads without any barrier recorded are assumed to be traversable.
4.2.2 AlignmentCodingAutomation Alignment values are coded from the outputs of a geospatial model that assigns curvature based on
degrees of turn per km.
4.2.3 CarriagewayWidthCodingAutomation The IRR model uses a matrix of lane and shoulder width to determine a carriageway risk score.
However, only the width of the carriageway is available in RAMM. As such, lane and median widths
are assumed in order to determine shoulder widths, as follows:
All local roads are assigned a lane width of 3.3 metres
All state highways are assigned a lane width of 3.6 metres
Roads with a road stereotype of “Divided – traversable” are assigned a 0.5 metre median
width
4.2.4 RoadsideHazardRiskCodingAutomation The coding of roadside hazard risk is the most difficult to automate. As such, roadside hazard risk is
estimated based on the land use and alignment codes, as shown in TABLE 4‐1.
Hazards are also identified manually where possible using high quality spatial imagery and
topographic maps.
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TABLE 4‐1: ROADSIDE HAZARD RISK CODING AUTOMATION
Land Use Code Alignment Code Approximated Roadside
Hazard Risk
No Access Any alignment Minor
Controlled Access Any alignment High/Moderate*
Urban Residential Any alignment Severe/Moderate*
Commercial Big Box/Industrial Any alignment Severe/Moderate*
Commercial Strip Shopping Any alignment Severe/Moderate*
Remote Rural Tortuous alignment High
Remote Rural Any alignment other than
tortuous
Moderate
Rural Residential Any alignment High/Moderate*
Rural Towns Any alignment Severe/Moderate*
*where more than one category is shown the average risk score associated with the categories listed
is used
4.2.5 LandUseCodingAutomation Land use coding has been automated using urban and rural boundaries and the density of residential
and commercial developments sourced from planning zones, Open Street Map (OSM) and Land
Information New Zealand (LINZ) datasets.
4.2.6 IntersectionDensityCodingAutomation Intersection density is coded by generating geospatial points at each intersection and calculating the
number of points per km for each corridor.
4.2.7 AccessDensityCodingAutomation Access density coding is assumed based on a combination of land use and posted speed limit as
follows:
1.35 ln 7.56 8.26 8.94 9.32 10.2611.13 11.17
Where:
AD = Access Density Bin
SL = Speed Limit (km/h)
CAU = Controlled Access (binary variable which equals 1 if land use is Controlled Access)
RemR = Remote Rural (binary variable which equals 1 if land use is Remote Rural)
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CBBI = Commercial Big Box/Industrial (binary variable which equals 1 if land use is Commercial Big
Box/Industrial)
RRes = Rural Residential (binary variable which equals 1 if land use is Rural Residential)
RT = Rural Town (binary variable which equals 1 if land use is Rural Town)
UR = Urban Residential (binary variable which equals 1 if land use is Urban Residential)
CSS = Commercial Strip Shopping (binary variable which equals 1 if land use is Commercial Strip
Shopping)
If ADB < 1.5, then code as <1 accesses/km
If ADB < 2.5, then code as 1 to <2 accesses/km
If ADB < 3.5, then code as 2 to <5 accesses/km
If ADB < 4.5, then code as 5 to <10 accesses/km
If ADB < 5.5, then code as 10 to <20 accesses/km
If ADB > 5.5, then code as 20+ accesses/km
4.2.8 TrafficVolumeCodingAutomation Traffic volume data stored in RAMM is used to automate the coding of traffic volume.
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AppendixA:RoadsideHazardRatingExamples
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Roadside
Hazard
Risk
Roadside Hazard Risk
Description
Example Photos
Severe Aggressive/severe continuous hazards and
cliffs, within 5m*
OR
20+ non‐frangible point hazards per kilometre
(1+ per 50m) or rigid
structures/bridges/
buildings, within 5m
High Cliffs or deep water at
5m to <10m*
Roll‐over up‐slopes and downslopes (e.g. >15⁰
and >1m high) at <5m*
Moderate Aggressive/severe and moderate continuous
hazards at 5m to <10m,
excluding cliffs and
deep water*
OR
20+ non‐frangible point hazards per kilometre
(1+ per 50m) or rigid
structures/bridges/buil
dings at 5m to <10m
OR
Deep ditches: >1m
deep, @ <5m
Roll-over slope (>15⁰ and >1m high),
@ <5m
Trees >10cm
diameter, @ <5m
Non-frangible poles,
@ < 5m
Ri id b ildi / t t @ 5
Semi-rigid structures or buildings, @ <5m
Water hazard @ <5m
Trees (non-frangible point hazards), @ 5m to <10m Roll-over slope (>15⁰ and >1m high),
@ 5m to <10m
Roll-over slope (>15⁰ and >1m high) @ <5m
Poles (non-frangible point
hazards), @ 5m to <10m
Rigid structures/buildings,
@ 5m to <10m
Aggressive vertical face,
@ <5m
Car parking @ <5m
Drop-off and water hazard @ 5m <10m
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Roadside
Hazard
Risk
Roadside Hazard Risk
Description
Example Photos
Car parking or semi‐
rigid structures or
buildings at <5m*
Minor Metal and concrete
safety barriers at <5m*
Car parking or semi‐
rigid structures or
buildings at 5m to
<10m*
Low Metal and concrete
safety barriers at 5m+*
Low severity property
damage hazards at any
distance*
All hazards at >=10m*
*over 50%+ of the length where they occur intermittently
Lightweight structures
e.g. Isolated rural letter boxes (<10cm diameter), hoardings
Small trees <10cm diameter
Safety barriers @ <5m
Only low severity property damage hazards within 10m
Only low severity property damage hazards
within 10m
Semi-rigid structures or buildings at 5m to <10m
Hazards 10m+, low severity property damage hazards
<10m