Since 2004, all states have had a per se BAC limit of 0.08 for noncommercial drivers age 21 and over. Since 1988, federal regulations have set a 0.04 per se BAC limit for commercial drivers (49 Code of Federal Regulations [CFR] 382.201), and all states have “zero tolerance” laws that specify per se BAC limits between 0.00 and 0.02 for drivers under 21. In a few states, different per se BAC limits apply to school bus drivers or convicted DWI offenders (NHTSA 2012a).
As described in chapter 4, laboratory studies have shown that driving-related performance is degraded at BAC levels as low as 0.01, and epidemiological studies employing crash data have shown significantly elevated crash risk at BAC levels near 0.05. Lowering per se BAC limits has been associated with reductions in impaired driving crashes and fatalities. For example, 14 independent studies conducted in the United States found that lowering the BAC limit from 0.10 to 0.08 resulted in reductions in alcohol-related crashes, fatalities, or injuries of 5–16 percent (Fell and Voas 2006, 233–43). Other studies have found similar results (for example, Dee 2001, 111–28; Shults and others 2001, 66–88; Voas, Tippetts, and Fell 2000, 483–92). In 2012, the CDC listed 0.08 per se BAC laws among the “top 20 violence and injury practice innovations since 1992” (Kress and others 2012, 257–63).
Several studies have also demonstrated the effectiveness of setting per se BAC limits below 0.08 for novice drivers, commercial drivers, or all drivers. For example, six studies that examined the effectiveness of low-BAC laws for young or novice drivers found reductions in injuries or crashes after enactment of the laws, and in three of the studies, the reductions were statistically significant (Zwerling and Jones 1999, 76–80). A study of commercial drivers found that changes to commercial driving laws, including the per se BAC reduction to 0.04, were associated with a 23 percent reduction in risk of alcohol involvement in fatal crashes by motor carrier drivers (Brady and others 2009, 775–82). A study of per se BAC reductions in several European countries (Albalate 2008, 20–39) found that the change from a 0.08 to a 0.05 per se BAC limit reduced traffic fatalities by 8–12 percent among people aged 18–49. Finally, in Australia, fatal crashes decreased significantly in two states (by 18 percent in Queensland and by 8 percent in New South Wales) after those states lowered their per se BAC limits from 0.08 to 0.05 (Henstridge, Homel, and Mackay 1997).
National and international traffic safety and public health organizations, including the American Medical Association (AMA 2013), the World Health Organization (WHO 2013a), the World Medical Association (WMA 2013), and the Association for the Advancement of Automotive Medicine (AAAM 2009) have advocated setting BAC limits at 0.05 or lower. The AMA, as part of its “Alcohol and the Driver” policy, has called for a per se BAC limit of 0.04 for more than two decades. The AAAM policy, established in 2009, included the following statement:
Because alcohol has been shown to have a wide variation of effect from subject to subject, special attention needs to be given to the selection of a BAC level in which the vast majority of drinking drivers are likely to be affected. This level appears to be .05 g/dL BAC. When all of the international evidence on lowering BAC limits is assembled, reviewed, and summarized, it is concluded that lowering the illegal BAC limit to .05 g/dL (or lower for countries that have had .05 g/dL limits for several years) is an effective strategy in reducing impaired driving. (AAAM 2009, 7)
According to information derived from the International Center for Alcohol Policies (ICAP) and the WHO, internationally, more than 100 countries have established maximum per se BAC limits at or below 0.05 (ICAP 2013 and WHO 2013b): these include 25 of the 27 EU member countries. The NTSB concludes that BAC levels higher than 0.05 are viewed by respected traffic safety and public health organizations around the world as posing unacceptable risk for driving, and more than 100 countries have already established per se BAC limits at or below 0.05.
Some countries have maintained a 0.08 per se BAC limit for criminal sanction but have recognized the driver-impairing effects of lower BAC levels by establishing lower BAC limits to be addressed by administrative sanction. For example, although Canada has set a 0.08 per se BAC level for DWI arrest, many Canadian provinces and territories provide for ALS for drivers beginning at BAC levels between 0.04 and 0.06 (Chamberlain and Solomon 2002, iii1–iii17). In Ontario, Canada, since May 2009, drivers with BACs between 0.05 and 0.08 face immediate license suspension and an administrative monetary penalty of C$150. Subsequent violations within a 5-year period lead to increasingly severe penalties, and drivers with more than three violations within 5 years are required to install an interlock on their vehicles for a 6-month period (Ontario Ministry of Transportation 2013).
Although lowering the per se BAC threshold may seem counterintuitive when the majority of alcohol-impaired drivers in fatal crashes have BAC levels well over 0.08, research on the effectiveness of laws limiting BAC levels (Hingson, Heeren, and Winter 1996; Wagenaar and others 2007) has found that lowering the per se BAC limit changes the drink-driving behavior of drivers at all BAC levels. Consequently, reducing the per se BAC limit could reasonably be expected to have a broad deterrent effect, thereby reducing the risk of injuries and fatalities from crashes associated with impaired driving.
The NTSB concludes that changing legal per se BAC limits from 0.08 to 0.05 or lower would lead to meaningful reductions in crashes, injuries, and fatalities caused by alcohol-impaired driving. Therefore, the NTSB recommends that the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia establish a per se BAC limit of 0.05 or lower for all drivers who are not already required to adhere to lower BAC limits. To further encourage states to implement this recommendation, the NTSB recommends that NHTSA seek legislative authority to award incentive grants for states to establish a per se BAC limit of 0.05 or lower for all drivers who are not already required to adhere to lower BAC limits. Similar incentive grants were used in the early 1980s to encourage states to establish 0.10 per se laws and to promote ALS/ALR for drivers arrested for DWI, and in the late 1990s to encourage states to establish 0.08 per se laws. In the most recent surface transportation reauthorization (MAP-21), grant funds are made available to states that adopt and enforce mandatory interlock laws for all convicted DWI offenders. Such grants can provide states with additional resources to raise awareness of new laws and to enforce them effectively.
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