Crash causes environmental

Using speed as a crash cause example was not done by chance. It was picked because speed is one behavior or human factor that can be (relatively easily) observed both in crash data and in traffic flow data. Environmental and vehicle factors can also be obtained in both types of data and are prime candidates for evaluation via the statistical approach. Other measures are more difficult. For example, alcohol involvement in crashes can be assessed if alcohol levels are obtained from the crash involved drivers (not too difficult to do) and from the general traffic population (much more difficult since it requires random stopping of drivers to check for their alcohol levels - even if they did not commit any traffic violation). Still other behaviors are practically impossible to evaluate statistically. Unfortunately the behaviors that fall into this category are the most frequent ones to emerge in the clinical evaluations attentional, perceptual, and decision failures. They are difficult to ascertain in the crash data (and are typically absent in police crash reports), and absolutely impossible to determine from the traffic population data. 

Risk is the probability of harm or loss and can be considered to be a product of the probability and the severity of specific consequences. Risk, as it relates to hazardous wastes and groundwater contamination, may be defined as the chance that humans or other organisms will sustain adverse effects from exposure to these environmental hazards. Risk is inherent in the life of all organisms—humans, animals, and plants. Tornadoes, landslides, hurricanes, earthquakes, and other natural disasters carry a risk of injury or death to any living thing in their path. Similarly, human-caused risks such as automobile accidents, plane crashes, and nuclear disasters occur with varying levels of severity. 

The first stage was considered to be a slow environmental stress crack (ESC), produced by slight chemical attack in the weld. ESC may be defined as a reduction in the tolerance of mechanical stress caused by special chemical environments, or, alternatively, as a reduction in the time to fracture under a fixed strain. Other examples have been the failure of blow-moulded polyethylene bottles when filled with detergent, and the weakening of crash helmets made of polycarbonate when affected by petrol or adhesive badges. 

The last part. Crash Causation and Countermeasures, focuses on what we have learned over the past one hundred years - and especially over the past few decades - about the causes of traffic accidents, their relative frequencies, and the means that have proven successfiil in combating accidents. The crash causation chapter also has a methodology component, because often the relative frequency of various causes of traffic accidents is methodology-bound meaning that different methods of analyses yield different conclusions. The countermeasures chapter is divided into first domains in which countermeasures can and have been applied organizational actions (such as "Vision Zero" mentioned above), behavioral changes in drivers and other road users, environmental treatments of the roadway and its furniture, and vehicular changes in both crash prevention and injury reduction. 

Figure 17-7, Human, environmental, and vehicular causes of crashes according to the Unsafe Driving Actions (UDA) study and the Indiana University Tri-Level study (from Hendricks et al, 2001)...

In contrast to a cause, a countermeasure can be defined by anofiier —more objective - criterion its effectiveness in crash prevention or its cost/benefit. This implies that while a cause can be identified as a human frctor the solution might be sought elsewhere. In fact, we see this all the time whenever a road is upgraded to a multi-lane divided highway the number of crashes -especially head-on crashes - diminishes greatly even though most of the crashes eliminated were caused by human errors . In the same context of driver errors that cause crashes, Anderson (1976) noted the nut behind the wheel myth does not account for the literally hundreds of documented studies which clearly indicate the value of environmental improvements in reducing accidents (pp. 20-21). Finally, a specific behavior - such as... 

---