Investigation of fatigue-related crashes on Australian roads

Fatigue represents a significant social and economic cost to the community in relation to road crashes, especially fatal road crashes. Fatigue-related crashes are often more severe than other crashes as drivers reaction times are often delayed or drivers have not employed any crash avoidance manoeuvres. However, the identification of fatigue related crashes is hindered by the absence of a universally accepted definition of fatigue. Furthermore, it is difficult to quantify the level of driver fatigue due to the difficulties in objectively measuring the degree of fatigue following a crash.

The Australian Transport Safety Bureau (ATSB) has proposed an operational definition of a fatigue-related road crash that would provide a common, objectively based methodology. This definition should be useful in monitoring fatigue-related crashes and gauging trends over time or between regions. The definition is based on a set of well researched selection criteria and uses crash characteristics routinely collected by different traffic authorities.

The criteria for the operational definition implemented in this report included single vehicle crashes that occurred during critical times (midnight-6am and 2pm4pm), and head-on collisions where neither vehicle was overtaking at the time of the crash. Excluded were crashes that occurred on roads with speed limits under 80 km/h, or involved pedestrians or unlicensed drivers or drivers with high levels of alcohol (blood alcohol concentration over 0.05g/100ml).

Using this criteria, this study found that 16.6 per cent of fatal crashes in 1998 involved driver fatigue. When comparing among the States and Territories, the Northern Territory had the highest rate of fatigue-related crashes per 100 million vehicle kilometres travelled (0.66). However, within individual States and Territories, New South Wales had the highest percentage of fatal crashes involving driver fatigue (22.0 per cent). The study also found that between 1990 and 1998 the proportion of fatal crashes involving driver fatigue increased from 14.9 per cent in 1990 to 18.0 per cent in 1994, after which there was a decline to 16.6 per cent in 1998. This trend was also observed when the number of fatigue-related crashes was worked as a proportion of all fatal crashes 80km/h or over. This was done to take into account the fact that the number of fatal crashes occurring in speed zones of 80km/h or over increased throughout the 1990s and that roads have also been re-zoned over this time period.

The operational definition identified a relationship between the time and type of fatigue related crashes. More single vehicle crashes occurred in the early morning (midnight- 6am) than the afternoon (2pm-4pm). However, the incidence of head-on crashes was highest between midday and 6pm and lowest between midnight and 6am, this relationship may be related to traffic densities. That is, higher traffic densities during the day would increase the likelihood of fatigue-related crashes involving multiple vehicles in head-on collisions and, conversely, lower traffic densities during the early morning would increase the likelihood of fatigue-related crashes involving single vehicles.

Some of the findings of this study were similar to other studies in that the operational definition identified a higher number of male fatigued drivers/riders than female, and more fatigued drivers/riders under 29 years of age compared with older age groups. The operational definition and other studies also found that most early morning fatigued drivers/riders were less than 29 years of age, and fatigued drivers/riders over 50 years of age were involved in more afternoon crashes than in early morning crashes.

There also appeared to be a relationship between the age of the fatigued driver/rider and the type of fatigue-related crash (single vehicle or head-on). Single vehicle crashes involved a higher proportion of fatigued drivers/riders under 29 years of age compared with head-on crashes. However, fatigued drivers/riders over 50 years of age were involved in more head-on crashes. This relationship may be linked to the time of crash. That is, single vehicle crashes are more likely to occur in the early morning and early morning crashes are more likely to involve fatigued drivers/riders under 29 years of age. Therefore, single vehicle crashes involve more fatigued drivers/riders under 29 years of age. A similar argument could explain the relationship between older fatigued drivers/riders and head-on crashes.

Using the operational definition, 29.9 per cent of fatal articulated truck crashes in 1998 involved driver fatigue, which was almost twice the proportion of all fatal crashes involving fatigue (16.6 per cent). However when speed limits were controlled for, by only including those crashes occurring at crash sites with speed limits of 80km/h or over, the difference between articulated truck crashes and all crashes was smaller. That is, in 1998, 34.5 per cent of fatal articulated truck crashes in speed zones of 80km/h or over involved fatigue, whilst 24.9 per cent of all fatal crashes involved fatigue.

The operational definition also found that the proportion of fatigue-related articulated truck crashes between 1990 and 1998 increased from 31.0 per cent in 1990 to 38.6 per cent in 1994, and this was followed by a decrease to 29.9 per cent 1998. Similar trends were also observed when speed zones were controlled, with an initial increase in the proportion of fatigue-related crashes between 1990 and 1994, followed by a decrease till 1998.

Although fatigue is more highly represented in articulated truck crashes, this does not necessarily imply that the truck driver was the fatigued driver in a crash involving more than one vehicle. The fatigued driver in a head-on crash was identified by observing which vehicle had driven onto the wrong side of the road. Therefore, in head-on fatigue related crashes involving an articulated truck, truck drivers were estimated to be the fatigued driver in only 16.8 per cent of crashes, whilst passenger car drivers were fatigued in 66.0 per cent of crashes.

The identification of fatigue-related crashes by the operational definition was compared with fatigue-related crashes identified by coroners/police. While researchers generally acknowledge that coroners/police underestimate the incidence of fatigue, it was the only measure available for comparison in this report. The operational definition compared relatively well; however, two

limitations and possible modifications for the operational definition were highlighted. Firstly, nearly two-thirds of crashes identified as fatigue related by coroners/police, but not by the operational definition, were excluded because they were single vehicle crashes that did not occur during the critical time periods. Secondly, just over a third of crashes identified as fatigue-related by the operational definition, but not by the coroners/police, had been attributed to speed, drugs, or drugs and alcohol by coroners/police. This may suggest that the operational definition should be modified to exclude speed and drug related crashes, and extend the critical time periods for single vehicle crashes. However, excluding drug and speed related crashes may reduce the objectivity of the operational definition and the ability to consistently implement the definition across various traffic authorities. For instance the identification of speed involvement can vary between different traffic authorities, and not all drivers involved in fatal crashes are tested for drugs. Furthermore, extending the critical time periods may lead to an increase in the number of crashes falsely identified as fatigue-related. Clearly, more analysis is needed before the definition is modified.

In conclusion, while the operational definition may include some crashes that are not fatigue-related and exclude others that are, it nevertheless provides a practical and useful index of the relative incidence of fatigue-related crashes.

Road fatal crash data research

Provides a single reference to frequently used historical road crash data for researchers, policy makers and other interested parties working in the area of road safety. It is based on data sourced from the Australian Transport Safety Bureau and the Australian Bureau of Statistics. It contains national data relating to fatal road crashes, population, vehicle registrations and kilometres travelled from 1925 to the present.

Potential Benefits and Costs of Speed Changes Assumption

1. The current speed limits on freeway standard and other divided rural roads are 110 km/h for cars and light commercial vehicles (LCVs) and 100 km/h for all rigid and articulated trucks, and the speed limit on undivided rural roads is 100 km/h for all types of vehicle.

2. Vehicles of each type cruise at their speed limit, so that their average speed is the same as the limit, unless their speed is reduced by slowing for curves or stopping in some parts of the road section.

3. Apart from where indicated, the rural roads are relatively straight without intersections and towns, allowing vehicles to travel at cruise speed throughout the whole road section.

4. The mix of traffic by vehicle type is the same on each class of rural road, namely 67% passenger cars, 20% light commercial vehicles, 5% rigid trucks and 8% articulated trucks, and that this mix does not vary by time of day on rural freeways and other divided roads.

5. Crashes involving material damage only, and no personal injury, were not included in the analysis of crash changes with speed, and the likely increase in these crashes with increased speeds (albeit to a lesser extent than fatal and injury crashes) was not valued. Material damage crashes represented about 16.3% of total crash costs in Australia during 1996 (BTE 2000).

6. Scenarios in which truck speed limits are lower than light vehicle limits have been analysed on the assumption that the (increased) speed differential between these vehicle types does not in itself increase crash risk or the severity of the crash outcome.

7. The changes in speed limits are assumed not to increase or reduce travel demand and traffic flows of each vehicle type on the road sections.

8. The travel time savings on the rural road sections are of sufficient magnitude to be aggregated and valued.

9. The current economic valuations of travel time, road trauma, and air pollution emissions provide an appropriate basis for analysis which summates their values, together with vehicle operating costs, in a way which represents the total social costs of each speed. In other words, the current valuations are an appropriate basis for ‘trading off’ these tangible and intangible values of each impact. (Results for some alternative valuations are also presented).

10. Assessment scenarios involving variable speed limit systems do not include any estimates of capital and maintenance costs for the systems.

11. Illustrative traffic volumes used in the analysis were 20,000 vehicles per day for freeways, 15,000 for divided highways and 1,000 for undivided roads.

Bicycle helmets to effective preventing head injury

Bicycle helmets have been proven to be effective in preventing head injury. Based on the research findings, it is possible to list the proven attributes required for an effective helmet design. The major research study supporting the factor is appended to the finding, often the attribute will have been mentioned in several studies.

• A helmet must be worn properly to be effective, Attewell et al (2001);


• Helmets are very effective in preventing skull fracture, but less effective in preventing brain injury, Henderson (1995).


• The helmet must remain on the head during the crash, Williams (1991);


• The helmet must remain in position during the crash, Williams (1991);


• The helmet must have the maximum possible coverage of the frontal and temporal areas of the head, Williams (1991), Cameron et al (1994) and McIntosh et al (1998);


• The helmet must have adequate energy attenuation characteristics, for a variety of impacted surfaces, including flat, blunt and sharp, Smith et al (1993);


• A drop energy requirement of between 1.5 and 2.2 metres appears to be adequate, Williams (1991) and Smith et al (1993);


• The criteria for the energy attenuation test should be in the region of 200g, McIntosh et al (1998);


• The helmet must retain its integrity during the impact, Ching et al (1997) and Williams (1991);


• The helmet must be retained, in case of a second impact, Williams (1991) and Smith et al (1993);


• A helmet with a hard shell appears to offer better protection from severe brain injuries, Rivara et al (1996);


• Severe brain injury occurs more often in impacts with other vehicles, McDermot et al (1993);


• The helmet for a young child needs to be different than for an older child or adult, Corner et al (1987).
  

Based on the review of the helmet effectiveness literature, there are several aspects of the helmet performance immediately before and during a crash, which need to be considered when reviewing the adequacy of a standard. These are grouped here into three requirements with a short explanation (with the related tests from the standard):

1. The helmet must be worn. A helmet must be worn to have any effect, must be attractive and comfortable for the wearer to be willing to wear it.

2. The helmet must remain in place during the crash. The retention system must be capable of keeping the helmet in place during the events immediately before (dynamic stability) and during (retention system strength) the crash.

3. The helmet must have adequate energy attenuation. The helmet must be capable of attenuating the impact to minimise injury. The helmet must cover the appropriate areas of the head; especially the frontal and temporal areas (test coverage). It must not disintegrate from the impact (helmet integrity) and must be capable of adequately minimising injury to the head resulting from impacts with different types of objects (energy attenuation and load distribution). The helmet must continue to remain in place on the head for a possible second impact (order of testing).