Studies Probe US Traffic Injuries, Deaths

Even as a new report documents substantial progress in reducing motor vehicle crashes and fatalities in the United States, recent research suggests that thousands of additional injuries and deaths could be prevented by lowering speed limits and banning drivers from engaging in potentially fatal distractions, such as dialing or text messaging on cellular telephones.

According to a report released in July by the National Highway Traffic Safety Administration (NHTSA), the number of traffic fatalities in 2008 reached its lowest level since 1961, when such statistics were first compiled. A second NHTSA report, also published in July, said that a 2007 survey monitoring weekend highway use recorded the lowest percentage of legally intoxicated drivers on the road since the agency's first survey more than 3 decades earlier. In addition to the curtailment of impaired driving, increased seat belt use, improved roadways, and safety-related vehicle features and design enhancements were cited as factors that contributed to reductions in motor vehicle crashes.

Despite such advances, research suggests that additional interventions could do much to further reduce highway deaths and crashes. A study released in July examining the effects of the repeal of federal speed limit controls in 1995 estimated that by the end of 2005, an estimated 12 545 additional deaths and 36 583 injuries could be attributed to the raised speed limits. In other work, researchers found that drivers of heavy vehicles and trucks who dialed or sent a text message on a cell phone substantially increased the risk of a crash or near-crash event. Although lowering speed limits and limiting driver distractions such as cell phone use and text messaging could make roads and highways safer, whether there is the political or societal will to implement such measures remains to be seen.

The NHTSA's statistical summary found that 37 261 people died in motor vehicle crashes in 2008, down 9.7% from the 41 259 who died in 2007. The 2008 fatality rate was 1.27 persons per 100 million vehicle miles traveled (VMT) vs 1.36 persons per 100 million VMT in 2007, a decrease of nearly 7% (http://www-nrd.nhtsa.dot.gov/Pubs/811172.pdf).

Early reports from 2009 suggest the downward trend in deaths is continuing, with one exception. Motorcycle-related deaths increased 2.2% between 2007 and 2008 to 5290, extending an 11-year trend.

The overall decrease in motor vehicle fatalities is partly due to fewer alcohol-impaired drivers on the road. The NHTSA survey found that 2.2% of weekend nighttime drivers in 2007 had blood alcohol levels of at least 0.08 g/dL compared with 4.3% of drivers in a 1996 survey and with 7.5% in 1973, when the study was first conducted (http://www.nhtsa.gov/staticfiles/DOT/NHTSA/Traffic%20Injury%20Control/Articles/Associated%20Files/811175.pdf). A further look at the numbers found that the time of the evening affected drunk driving rates: 1.2% of drivers were intoxicated between 10 PM and midnight and 4.8% of late-night drivers were legally intoxicated between 1 AM and 3 AM. The type of vehicle was also associated with varying intoxication levels, with 5.6% of motorcycle drivers were legally impaired compared with 0.3% of minivan operators.

For the first time, the survey also looked at drug use and found that more than 16% of nighttime weekend drivers tested positive: 8.6% for marijuana, 3.9% for cocaine, and 3.9% for potentially impairing over-the-counter and prescription drugs. The findings were based on random stops of nearly 11 000 drivers at 300 locations throughout the United States. These drivers, who participated voluntarily and anonymously, underwent a number of evaluations, including blood tests. The survey authors cautioned that their data do not imply that those testing positive for drugs were impaired at the time of testing because a drug’s presence can, in some cases, be detected long after its use. Also, the impairment effects for various concentration levels of different drug types has not yet been studied rigorously.

In addition to interventions aimed at improving safety on the roads, there is an additional factor contributing to the nearly 10% decline in highway deaths in just 1 year, said James C. Fell, MS, senior program director with the Pacific Institute for Research & Evaluation. “There's a couple reasons why deaths are down. Seat belt usage is up, and that is saving lives,” he said. “But the real reason is the recession.” Individuals are driving fewer miles and are curtailing discretionary travel, such as going to restaurants, he noted.

Some researchers say there is evidence suggesting that highway deaths could be reduced even further by lowering speed limits. This evidence, they say, emerged after the US Congress enacted the National Highway Designation Act in 1995. This law removed all federal speed limit controls (including the 1974 National Maximum Speed Law, which set a 55 miles per hour [mph] limit on all interstate roads) and allowed states to set their own maximum limits, as high as 80 mph in Montana and Texas. In the 10 years following passage of this law, there was a 3.2% increase (an estimate based on modeling) in road fatalities attributable to raised speed limits, with the highest increases seen on rural interstates (9.1%) and urban interstates (4.0%) (Friedman LS et al. Am J Public Health. 2009;99[9]:1626-1631).

“Proponents of deregulation of speed . . . claim that higher travel speeds do not result in higher numbers of deaths, and it is better for the economy” said Lee S. Friedman, PhD, lead author and assistant professor at the University of Illinois at Chicago School of Public Health. “Our goal was to see the long-term impact.”

Attempts to reduce the speed limit face societal and economic pressures, but lowering it to 55 mph would likely save lives, said Friedman. Risk rates from crashes are not linear but exponential; the greatest risk of death occurs above 35 mph, with minimal risk under that speed. “Most people do not crash at high speed; most hit their breaks before impact,” Friedman said. “So if you are going 55 mph, the ability to get down below 35 mph is much greater.”

While physics plays an important role in crashes, so too does human behavior, in the form of driver distraction. Drivers have long diverted their focus from attentive driving to turn a radio dial, converse with passengers, and consume food or a beverage. Now, however, dialing cell phones and texting have raised the threat to highway safety, according to investigators with the Virginia Tech Transportation Institute in Blacksburg.

In a study of truck drivers that is a follow-up to their 2006 study on distractions among those driving cars, the researchers installed small video cameras and other measuring devices in 55 trucks and followed up 203 drivers (who volunteered to participate in the study) for more than 6 million miles. The research tallied 21 crashes and 4500 “safety events” that included a range of mishaps from near-collisions to unintended lane deviation. The measuring devices and video cameras then allowed the researchers to determine what the driver was doing just before an incident.

The research team found that compared with nondistracted drivers, drivers dialing a cell phone had a 5.9 times greater risk of crashing or nearly crashing; those using or reaching for an electronic device were 6.7 times more likely to have a crash or a near miss. The study, the first to investigate the effects on crash risk of reading and sending text messages, also found that texting increased the danger by 23.2 times. Surprisingly, the researchers also found that talking into or listening to a cell phone did not increase risk—a finding that contradicts previous studies that have suggested an increased risk (http://www.vtti.vt.edu/PDF/7-22-09-VTTI-Press_Release_Cell_phones_and_Driver_Distraction.pdf).

“What we saw is that the visually intense tasks, like dialing, texting, and reaching, took the driver's forward-looking eyes off the roadway for almost 6 seconds,” said Rich Hanowski, PhD, director of the institute's Center for Truck and Bus Safety. “Such diversion was associated with the highest risk. What we did not see was the same risks associated with cognitive tasks, like talking and listening.”

Hanowski's findings showed that the risks posed by these types of diversions were higher than those seen in their car study. This difference might be because trucks are heavier and larger, making driving corrections more difficult, he said. However, he noted, the higher risk rates might also reflect the fact that cell phones and other devices have become more complicated to operate in the past few years and require more time spent manipulating them. What is clear, Hanowski said, is that “there is no safety argument to be made for texting while driving; a survey found the majority of the population says it is a crazy thing to do.”

Despite this sentiment, changing such unsafe behaviors will be very difficult.

“The fact is that while most people think talking on the cell phone is not safe behavior, it is on the increase and the laws prohibiting it are often not effectively enforced,” said Adrian Lund, PhD, president of the Insurance Institute for Highway Safety. Nonetheless, changing behaviors can be done, he added. “The question has a political answer,” he said.

Incorporating “passive technologies” in new vehicles also offers the potential of harm reduction on the road. Fell said that it may be about 10 years away, but engineers are developing technologies designed to stabilize a vehicle to prevent it from rolling over, to automatically reduce speed when the vehicle runs off the road, to apply brakes when sensors signal an imminent crash, and to prevent a vehicle from starting if the driver's blood-alcohol level is too high.

In the meantime, Fell agrees with Lund that old-fashioned methods can still work. “We have to change drivers' attitudes,” he said. “And if there is visible enforcement—that, for example, the police will stop you if they see you texting—that will be effective.”