How does AusRAP star rate roads for safety?
 
 






The AusRAP star ratings were developed by the Australian motoring clubs with assistance from ARRB Group

 

What are star ratings?

  

 

Star rating a road is a proactive approach to road safety. It enables sections of road with a relatively high level of risk to be identified before a crash occurs.

 

The degree of risk, or just how safe a road is, depends to an extent on whether safety has been built-in to it through the inclusion of design elements such as wide lanes and shoulders and safety barriers, which are known to have an impact on the likelihood of a crash and its severity.

 

The best roads are likely to be straight, have dual divided carriageways with good line-marking, wide lanes and sealed shoulders, safe roadsides and few, if any intersections.

 

The least safe roads are likely to be single lane (undivided) with lots of curves in mountainous terrain, with narrow lanes and sealed shoulders, poor line marking and severe roadside conditions such as trees and poles.

 

Star rating is based on inspection of these various design elements and rating the impact which they have on the likelihood of a crash and its severity. This approach to road safety assessment is increasingly being taken up internationally. Similar types of road inspection programs are now undertaken by EuroRAP in countries such as Sweden, Germany, Austria, Britain, Iceland, Netherlands, Spain and Switzerland. In many countries, the star rating process is driving the development of innovative engineering for safer roads.

 

This approach is also driving innovative engineering programs in Australia. In Victoria for example, the $130 million Safer Roads Program aims to significantly address run-off road crashes, which represent a substantial proportion of all casualty crashes.

 

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How is the data collected?

  

 

AusRAP star ratings are based on a detailed visual inspection of a road’s design elements. AusRAP used an innovative approach to undertake these inspections by obtaining State and Territory road authorities’ “video” data of road networks, which is usually collected for asset management purposes.

 

The data was collected using specially equipped vehicles which record digital photographs, or images, of a road (generally at 5m to 10m intervals) using an array of cameras aligned to pick up various views of the road (forward, rear, side-left and side-right). The vehicles are able to drive along the road at almost normal speed while collecting this information.

 

 

The digital images are “streamed” together to form a “video” of the road network. Analysts then undertake desk-top inspections by taking a virtual drive-through of the road network (see Figure 4), at highway speed or on a frame-by-frame basis, depending on the complexity of the road. The software used by the analysts enables accurate measurements to be made of elements such as lane widths, shoulder widths and distance between the road edge and fixed hazards, such as a trees or poles.

 

 

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Which road design elements are inspected?

  

 

A road’s star rating is based on an inspection of design elements which are known from extensive research to influence the likelihood of crashes occurring and the severity of those crashes that do occur.

 

The focus of the star ratings is on the design elements which influence the three most common and severe types of crash on rural highways: run-off road crashes (which account for around half of all crashes), head-on crashes and crashes at intersections. Together, these three crash types account for around three quarters of all crashes on rural highways.

 

The design elements that influence run-off road and head-on crashes which are analysed by AusRAP include:

 

  • whether opposing traffic lanes are separated by a physical barrier or wide median (that is, whether the road is divided or undivided);

  • lane width;

  • sealed shoulder width;

  • alignment (that is, number and sharpness of curves);

  • terrain (that is, flat, rolling or mountainous);

  • line marking;

  • whether roadsides are free of hazards like trees and poles or have safety barriers in place;

  • traffic speeds; and

  • overtaking provision.

  

The design elements that influence intersection crashes which are analysed by AusRAP include:

 

  • type of intersection (for example, over-pass or under-pass, T-junction, cross roads or railway);

  • volume of traffic on side road (or railway);

  • traffic speeds;

  • alignment of side roads (or railway);

  • sight distances; and

  • right and left turn provision.

 

 The star rating system includes measures of how well traffic lanes are separated…

 …checks for roadside protection

…and intersection design and frequency.

 

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The Road Protection Score (RPS)

  

 

At the heart of the star ratings is the Road Protection Score (RPS). The RPS approach to assessing the safety of a road was developed by ARRB Consulting and the Australian motoring clubs. It builds on work undertaken by the European Road Assessment Program (EuroRAP) and draws extensively on the research conducted by Austroads and ARRB in the development of the Road Safety Risk Manager.

 

This research enables a relative risk score to be determined for each of a road’s design elements. As a simple example, the risk of being involved in a crash on a road with narrow lanes (less than 2.8m wide) is 50 per cent higher than on a road with wide lanes (greater than 3.6m wide). That is, other things being equal, a road with wide lanes is safer—and therefore receives a better score—than a road with narrow lanes. Narrow lanes leave little room for error.

 

As another example, the risk of being involved in a crash on a road with no sealed shoulders is 60 per cent higher than on a road with wide sealed shoulders (greater than 2.4m). That is, other things being equal, a road with wide sealed shoulder is safer—and therefore receives a better score—than a road with no sealed shoulders.

 

And roads which are divided—that is, those which separate opposing traffic flows—are much safer than undivided roads, which are separated by no more than a splash of paint.

 

 

A Road Protection Score (RPS) is calculated for each of the three crash types: run-off road crashes, head-on crashes and intersection crashes. The scores are based on the various design elements (listed earlier) which are weighted according to the relative contribution that each design element makes to likelihood of a crash. The scores are further adjusted according to the likely severity of a crash should one occur.

 

The final RPS is determined by combining the run-off road RPS, head-on RPS and intersection RPS for sections of road that are generally homogeneous. These sections can be as short as 200 metres or as long as 100km, depending on the frequency of changes in the road’s design.

 

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Star ratings

  

 

The RPS can be plotted in chart form for every highway . Along the horizontal axis is the distance in kilometres from the start of a highway and on the vertical axis is the RPS. The chart highlights the fact that as a motorists drive along a highway, the crash risk they face changes constantly as the road design elements vary.

 

In circumstances where highways are dual divided carriageway, a RPS is calculated for both directions.

 

The scores are allocated to one of five star rating bands.  The star rating system reflects the typical international practice of recognising the best performing category as 5-star and the worst as 1-star.

 

 

The star ratings are presented in map form.  For the purpose of mapping, highways have been split into shorter links which are generally defined by using two criteria. First, the links should be meaningful and distinct to road users (that is, start and end at identifiable locations).

 

Since risk scores—and thus star ratings—often fluctuate over a given length of road, the second criteria we have used is to assigned the predominant star rating to a link.

 

The typical road stereotypes for roads with different star ratings are shown below.

 

 

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