Effects of Alcohol on Performance

Alcohol affects mood and behavior, causing euphoria (which is particularly significant in risk taking) but also depressing the central nervous system (CNS). Even at low doses, there is clear evidence that alcohol impairs performance, especially as the faculties that are most sensitive to alcohol are those most important to driving, namely complex perceptual mechanisms and states of divided attention. In a review of more than 200 articles (18), several behavioral aspects were examined, including reaction time, tracking, concentrated attention, divided attention, information processing, visual function, perception, psychomotor performance, and driver performance. Most of the studies showed impairment at 70 mg/100 mL of blood, but approx 20% showed impairment at concentrations between 10 and 40 mg/ 100 mL of blood.

The definitive study on the relationship between risk of accident and blood alcohol concentration is that conducted in the 1960s in Grand Rapids, Mich., by Borkenstein and Dale (19); data were collected on 5895 drivers involved in accidents and on 7590 drivers not involved in accidents. Comparison of the two groups disclosed that an accident was statistically more likely at blood alcohol levels greater than 80 mg/100 mL of blood, with accidents occurring more frequently as follows:

Blood alcohol (mg/100 mL) Accident occurrence

50-100 1.5 times as frequently

100-150 4 times as frequently

Over 150 18 times as frequently

Further analysis of the data by Allsop (20) quantified the risks for different ages and different drinking habits. On average, the risk doubles at 80 mg/ 100 mL, increasing sharply to a 10 times risk multiplier at 150 mg/100 mL and a 20 times risk multiplier at 200 mg/100 mL of blood. For inexperienced and infrequent drinkers, the sharp increase occurs at much lower levels, whereas for the more experienced drinking driver it may not occur until 100 mg/100 mL (Fig. 1).

Therefore, this research has encouraged some countries to have a lower blood alcohol level for legal driving; in Australia, Canada, and some states of the United States, different levels and rules are applied for younger and/ or inexperienced drivers (see Subheading 3.3.). Further evidence of the relationship between crash risk and blood alcohol levels has been shown by Compton and colleagues (21), who studied drivers in California and Florida. This recent research studying a total of 14,985 drivers was in agreement with previous studies in showing increasing relative risk as blood alcohol levels increase, with an accelerated rise at levels in excess of 100 mg/100 mL of blood. However, after adjustments for missing data (hit-and-run drivers, refusals, etc.), the result was an even more dramatic rise in risk, with the relative risk of crash involvement being significantly elevated at blood alcohol levels of 40 mg/100 mL.

BfACGigfl 00ml} 0 10 20 35 50 1 0 70 SO

BfACGigfl 00ml} 0 10 20 35 50 1 0 70 SO

0 10 50 90 100 150 m

0 10 50 90 100 150 m

Fig. 1. Risk of road traffic accidents related to level of alcohol in the blood and breath. BAC, blood alcohol concentration; BrAC, breath alcohol concentration. Permission by Greenwich Medical Media.

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