Nearly half of American adults — 45 percent — say they have driven while struggling to keep their eyes open and focused on the road ahead. That finding, from a September survey of 2,003 people by the American Academy of Sleep Medicine, supports the organization’s belief that drowsy driving is a serious public health concern. The AAA Foundation for Traffic Safety, a nonprofit research-and-education organization, estimates that more than 300,000 accidents a year, including 6,400 fatal accidents, stem from drowsy driving. Data released by the foundation last year, from what’s called a “naturalistic driving study” that used in-vehicle cameras and other data collection equipment to monitor 3,593 drivers for several months, found that about 10 percent of all vehicle crashes result from driver drowsiness. Common symptoms of drowsiness while driving include yawning and head drooping, drifting out of a lane, missing road signs or turns, having trouble maintaining a regular speed and not being able to remember the last few miles, according to the academy. Sleep and safety experts say that drinking caffeinated beverages, turning up the radio or cooling the vehicle by opening windows or upping the air conditioning may help temporarily, but pulling off the road to take a break is a much safer response.