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17 CHAPTER 4 FACTORS RELATED TO DRIVER RISK This chapter reviews personal factors relevant to com- drivers, in 2001, those aged 25 or younger constituted 6.9% of mercial driver crash risk, including driver age and gender, the large truck drivers involved in fatal crashes, 11.3% of those driving history, non-driving history, medical conditions and involved in injury crashes, and 13.8% of those involved in health, fatigue susceptibility, personality traits, sensory- property damage only (PDO) crashes (FMCSA 2003). These motor performance capabilities, and several other personal statistics are hard to evaluate, because the relative mileage crash risk factors. exposure of young commercial drivers is not known. In addition, younger truck drivers tend to be hired by smaller, 4.1 DRIVER AGE AND GENDER shorter-haul companies and are more likely to drive large single-unit (straight) trucks than their older peers (Blower 4.1.1 Age 1996, Corsi and Barnard 2003). So, even if rates and risk metrics could be generated, direct comparisons of them For the overall driver population, age is one of the strongest would not necessarily be valid. personal factors affecting crash involvement (NHTSA 2000). A detailed statistical analysis of young truck driver involve- Teenaged drivers, especially males, have crash involvement ment in crashes was conducted by Blower (1996) using Michi- rates per mile traveled that are several times higher than those gan and North Carolina crash and violation data. Young truck of the adult population. Driver errors seen in teenaged drivers drivers (defined in this study as 18 to 21 years old) had mov- include both risk-taking behaviors and misjudgments (Mayhew ing violation rates that were almost twice those of the middle- and Simpson 2003). Even drivers in their twenties--especially aged drivers (30 to 49 years old) in the study. Speeding above early twenties--have high crash rates. Across the spectrum of the speed limit and unsafe speeds for conditions were the two driver ages, crash rates reach their lowest levels for drivers in top violations cited. The study did not report crash involve- their 40s and 50s, remain relatively low for drivers in their 60s, ment rates, again due to lack of reliable mileage exposure and begin to rise for drivers in their 70s. Drivers aged 85 and data. However, the study did report that young commercial older have crash rates (per mile traveled) that rival those of drivers were about 50% more likely than middle-aged drivers new teenaged drivers. to be charged with a violation in a crash. In two-vehicle crashes Inexperience is probably not the main factor elevating the with light vehicles, the young truck driver was twice as likely crash risk of teenaged drivers. Pierce (1977) studied the crash as the other driver to be charged with a hazardous action or rates of 16- to 19-year-olds and found evidence contrary to the traffic violation, which is opposite the trend for large hypothesis that experience is the primary factor. He found that truck/light vehicle crashes in general (FMCSA 2003). Major 14.2% of drivers licensed at 16 years old had vehicle crashes, crash scenarios for these young truck drivers were loss of compared with 13.4% in their second year and 11.5% in their control/struck fixed object, backing into another vehicle, third year (at the age of 18). Drivers who waited until age 18 turning-related involvements, and rear-end (truck-striking) to receive their license had a comparable crash rate with those crash involvement. who had been driving for 3 years (i.e., 11.9%). Nineteen-year- In the local/short-haul study described earlier in the syn- olds who were licensed since the age of 16 had a crash thesis, Hanowski et al. (2000) analyzed factors (including involvement percentage of 10.2% while the same age group both personal driver factors and situational factors) predicting who were newly licensed had an involvement percentage of truck driver involvement in critical incidents (caused by the 10.5%. It appears that other characteristics such as immaturity truck driver). They evaluated driver age, ambient illumina- or risk-taking play stronger roles in the high crash rates of tion, prior night's sleep, current drowsiness rating, physical young drivers than do lack of driving experience per se or any work requirements for the day, and several other factors. They lack of physical ability. Ulleberg (2002) found that young, found that driver age was the strongest predictor of critical high-risk drivers demonstrated a risk-taking attitude that incident involvement. resulted in a propensity to engage in risky driving behaviors. In a study of driver attributes and rear-end crash involve- The above studies and statistics related to all drivers-- ment among the general driving population, Singh (2003) commercial plus non-commercial. Regarding commercial found that young drivers (younger than 25 years old) were