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Methodology

In this section you will find two series of documents. The 'iRAP Methodology' fact sheets describe the  Star Rating and Safer Roads Investment Plan methodologies, while the 'iRAP Road Attribute Risk Factors' fact sheets describe the risk factors used in the models.

 
iRAP Methodology Fact Sheet 1: Overview

This fact sheet provides an overview of the Star Rating and Safer Roads Investment Plan processes and a list of factsheets in the series.

 
 
iRAP Methodology Fact Sheet 2: Development History

This fact sheet provides an overview of the Star Rating and Safer Roads Investment Plan development history.

 
 
iRAP Methodology Fact Sheet 3: Road Attributes

This fact sheet lists the road attributes included in iRAP assessments.

 
 
iRAP Methodology Fact Sheet 4: Crash Types

This fact sheet provides an overview of the road users, crash types and crash initiation modes used in the models.

 
 
iRAP Methodology Fact Sheet 5: External Flow and Median Traversability

This fact sheet describes External Flow Influence factors, which account for the way in which traffic flows can affect the type of crash that an individual road user is involved in. It also describes Median Traversability factors, which account for the potential that an errant vehicle will cross a median and also reflects the oncoming flow in the opposing direction.

 
 
iRAP Methodology Fact Sheet 6: Star Rating Score Equations

This fact sheet describes the iRAP Star Rating Score equations.

 
 
iRAP Methodology Fact Sheet 7: Star Rating Bands

This fact sheet describes the Star Rating bands and how they were set.

 
 
iRAP Methodology Fact Sheet 8: Smoothed Star Ratings

This fact sheet provides an overview of the process used to smooth Star Ratings.

 
 
iRAP Methodology Fact Sheet 9: Star Rating Worked Example

This fact sheet includes a worked example of the way in which Star Ratings are calculated.

 
 
iRAP Methodology Fact Sheet 10: Casualty Estimation and Calibration

This fact sheet describes how the number of casualties (fatalities and serious injuries) is estimated and how the models are calibrated.

 
 
iRAP Methodology Fact Sheet 11: Countermeasures

This fact sheet describes the road safety countermeasures used in the methodology.

 
 
iRAP Methodology Fact Sheet 12: Multiple Countermeasures

This fact sheet describes how the effectiveness of a countermeasure is estimated when it is used in combination with other countermeasures.

 
 
iRAP Methodology Fact Sheet 13: Economic Analysis

This fact sheet describes the economic analysis used to prioritise countermeasure options.

 
 
iRAP Methodology Fact Sheet 14: Star Ratings for Schools

This fact sheet describes the background research and development associated with the Star Rating for Schools methodology. 

 
 
iRAP Road Attribute Risk Factors: Lane Width

This factsheet describes the road attribute risk factors used in the iRAP methodology for Lane Width. Lane Width is the distance from the centre of the shoulder marking to the centre of the adjacent lane marking or the centreline marking.

 
 
iRAP Road Attribute Risk Factors: Number of Lanes

This factsheet describes the road attribute risk factors used in the iRAP methodology for Number of Lanes. Number of Lanes records the total number of lanes in the direction of travel. 

 
 
iRAP Road Attribute Risk Factors: Delineation

This factsheet describes the road attribute risk factors used in the iRAP methodology for Delineation. Delineation is a measure of the road attributes that inform drivers of road conditions to keep them within the driven lane and aware of road ahead. 

 
 
iRAP Road Attribute Risk Factors: Curvature

This factsheet describes the road attribute risk factors used in the iRAP methodology for Curvature. Curvature is a measure of the horizontal alignment of a road. 

 
 
iRAP Road Attribute Risk Factors: Quality of Curve

This factsheet describes the road attribute risk factors used in the iRAP methodology for Quality of Curve. Quality of Curve is a measure how easy it is to judge how sharp a curve is and if it can be driven safely.

 
 
iRAP Road Attribute Risk Factors: Grade

This factsheet describes the road attribute risk factors used in the iRAP methodology for Grade. Grade is a measure of the gradient of the road along its length. It refers to both upward and downward grades. 

 
 
iRAP Road Attribute Risk Factors: Speed Management / Traffic Calming

This factsheet describes the road attribute risk factors used in the iRAP methodology for Speed Management/ Traffic Calming. Speed Management/Traffic Calming records the presence of facilities judged to have the ability to reduce the operating speed 10km/h below the speed limit (on roads adjacent to or adjoining the traffic-calmed sections).  

 
 
iRAP Road Attribute Risk Factors: Road Condition

This factsheet describes the road attribute risk factors used in the iRAP methodology for Road Condition. Road Condition records the degree to which the road has an even surface that does adversely affect the travel path of vehicles, motorcycles and bicycles.  

 
 
iRAP Road Attribute Risk Factors: Skid Resistance / Grip

This factsheet describes the road attribute risk factors used in the iRAP methodology for Skid Resistance/Grip. This attribute records the general characteristics of the road surface with regard to grip.  Formally, it relates to the force developed when a tire that is prevented from rotating slides along the pavement surface (Highway Research Board, 1972).  

 
 
iRAP Road Attribute Risk Factors: Street Lighting

This factsheet describes the road attribute risk factors used in the iRAP methodology for Street Lighting. Street Lighting records the presence of lighting that is sufficient to provide illumination for vehicle occupants, motorcyclists, pedestrians and bicyclists.  

 
 
iRAP Road Attribute Risk Factors: Sight Distance Restriction

This factsheet describes the road attribute risk factors used in the iRAP methodology for Sight Distance Restriction. Sight Distance Restriction refers to the ability of a driver or motorcycle rider to see pedestrians or bicyclists either in the roadway or about to cross the road ahead, or vehicles or motorcycles at an intersection.  

 
 
iRAP Road Attribute Risk Factors: Intersection Type

This factsheet describes the road attribute risk factors used in the iRAP methodology for Intersection Type. Intersection Type records the presence and type of intersections with gazetted/adopted roads. 

 
 
iRAP Road Attribute Risk Factors: Intersection Channelisation

This factsheet describes the road attribute risk factors used in the iRAP methodology for Intersection Channelisation. Intersection Channelisation records if there are raised or coloured islands present at an intersection that designate intended vehicle paths. 

 
 
iRAP Road Attribute Risk Factors: Intersection Quality

This factsheet describes the road attribute risk factors used in the iRAP methodology for Intersection Quality. Intersection Quality is a measure of the intersection design, advance warning, signing, and marking.

 
 
iRAP Road Attribute Risk Factors: Property Access Points

This factsheet describes the road attribute risk factors used in the iRAP methodology for Property Access Points. Property Access Points records the number of low-flow points where vehicles can enter or exit the roadway. This includes commercial and residential driveways and minor access lanes.  

 
 
iRAP Road Attribute Risk Factors: Roadside Severity - Distance

This factsheet describes the road attribute risk factors used in the iRAP methodology for Roadside Severity - Distance. Roadside Severity – Distance is a measure of the distance between the edge of the road and the nearest roadside object that would result in death or serious injury to a vehicle occupant, motorcyclist or bicyclist if struck.

 
 
iRAP Road Attribute Risk Factors: Roadside Severity - Object

This factsheet describes the road attribute risk factors used in the iRAP methodology for Roadside Severity - Object. Roadside Severity – Object records the nearest object that could result in death or injury to vehicle occupants, motorcyclists and bicyclists if struck. The object recorded is the same as that referred to in Roadside Severity – Distance.

 
 
iRAP Road Attribute Risk Factors: Paved Shoulder Width

This factsheet describes the road attribute risk factors used in the iRAP methodology for Paved Shoulder Width.  Paved Shoulder Width refers to the driveable section of pavement outside the edge line.

 
 
iRAP Road Attribute Risk Factors: Shoulder Rumble Strips

This factsheet describes the road attribute risk factors used in the iRAP methodology for Shoulder Rumble Strips. Shoulder Rumble Strips (also referred to as raised profile edge lines or audible edge lines) can be used to delineate the edge of paved roads. As well as providing visual delineation, Shoulder Rumble Strips can also be heard and felt by drivers and riders.

 
 
iRAP Road Attribute Risk Factors: Centreline Rumble Strips

This factsheet describes the road attribute risk factors used in the iRAP methodology for Centreline Rumble Strips. Centreline Rumble Strips (also referred to as raised profile centre lines or audible centre lines) can be used to delineate the centre of paved roads. As well as providing visual delineation, Centreline Rumble Strips can also be heard and felt by drivers and riders.

 
 
iRAP Road Attribute Risk Factors: Median Type

This factsheet describes the road attribute risk factors used in the iRAP methodology for Median Type. Median Type records the road infrastructure that separates opposing traffic flows. 

 
 
iRAP Road Attribute Risk Factors: Pedestrian Crossing Facilities

This factsheet describes the road attribute risk factors used in the iRAP methodology for Pedestrian Crossing Facilities. Pedestrian Crossing Facilities records the presence of purpose built facilities to assist pedestrians.

 
 
iRAP Road Attribute Risk Factors: Pedestrian Crossing Quality

This factsheet describes the road attribute risk factors used in the iRAP methodology for Pedestrian Crossing Quality. Pedestrian Crossing Quality records how well the crossing can be seen by drivers or if there are warning signs.

 
 
iRAP Road Attribute Risk Factors: Pedestrian Fencing

This factsheet describes the road attribute risk factors used in the iRAP methodology for Pedestrian Fencing. Pedestrian Fencing records if there is a fence present that is sufficient to restrict pedestrian crossing flow.

 
 
iRAP Road Attribute Risk Factors: Sidewalk Provision

This factsheet describes the road attribute risk factors used in the iRAP methodology for Sidewalk Provision. Sidewalk Provision refers to the provision of an area (a sidewalk or footpath) at the side of the road for pedestrians. The sidewalk can be either ‘formal’ or ‘informal’.

 
 
iRAP Road Attribute Risk Factors: Facilities for Motorcycles

This factsheet describes the road attribute risk factors used in the iRAP methodology for Facilities for Motorcycles. Facilities for Motorcycles records the presence of purpose-built facilities for motorised two wheelers.

 
 
iRAP Road Attribute Risk Factors: Facilities for Bicycles

This factsheet describes the road attribute risk factors used in the iRAP methodology for Facilities for Bicycles. Facilities for Bicycles records the presence of purpose-built facilities for non-motorised vehicles.

 
 
iRAP Road Attribute Risk Factors: Vehicle Parking

This factsheet describes the road attribute risk factors used in the iRAP methodology for Vehicle Parking. Vehicle Parking records the extent to which there is parked vehicles obstruct pedestrians or bicyclists.

 
 
iRAP Road Attribute Risk Factors: Service Road

This factsheet describes the road attribute risk factors used in the iRAP methodology for Service Road. Service Road records the present of a service road running parallel with main carriageway.  The purpose of a service road is to link the property access and minor intersections together and then join them to the main carriageway at specific point. Note that in the literature the term “frontage road” is also used to describe this attribute.

 
 
iRAP Road Attribute Risk Factors: Operating Speed

This factsheet describes the road attribute risk factors used in the iRAP methodology for Operating Speed and Mean Speed. Operating Speed is used in the calculation of Star Ratings and is the greater of the posted (or official) speed limit or 85th percentile speed. Casualty estimations and economic analyses (in the Safer Roads Investment Plans) are based on mean speeds.

 
 
iRAP Road Attribute Risk Factors: School Zone Warning

The fact sheet covers the range of advance warning provided for schools.

 
 
iRAP Road Attribute Risk Factors: Full Reference List

This factsheet provides a complete list of citations used in the selection of iRAP road attribute risk factors.

 
 
 
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