Hitting the road for a New Year's gathering? Crossing the highway rumble strip is a sign that you're too sleepy to drive, researchers report.

Sleepiness affects your ability to make decisions, and ignoring a rumble strip could make you prone to a deadly crash, they added.

"Pulling over and taking a 15-20 minute nap or drinking a double shot of coffee have been found to be the most effective ways of increasing driver alertness and reducing sleepiness," study author Chris Watling, of Queensland University of Technology's Centre for Accident Research & Road Safety-Queensland in Australia, said in a university news release.

Researchers from Queensland, the Stress Research Institute of Stockholm University and the Swedish Road and Transport Research Institute observed 36 people during a 90-minute simulated driving session.

"What we found was the first rumble strip hit reduced sleepiness, but repeated hits did not increase alertness, demonstrating sleepiness levels were linked to a greater probability of hitting a rumble strip," Watling said in a Queensland University news release.

Previous studies found rumble strips help prevent car accidents but are not a foolproof solution for sleepy driving, the study published recently in the Journal of Sleep Research said.

The findings suggest that sleepiness increases over the duration of a drive, Watling said.

"It is very possible that a driver will run off the road despite the presence of rumble strips if they ignore an early rumble strip hit and decide to continue driving when highly sleepy."

The study authors recommend that drivers build in time for breaks to manage fatigue on long road trips. Drivers should also take a break if they notice signs of sleepiness such as yawning, blinking more often and shifting positions in the seat.

The researchers noted that trouble concentrating and difficulty keeping the eyes open are signs of more extreme sleepiness.

"Ideally, drivers should stop driving and use a sleepiness countermeasure after noticing some of the early signs of sleepiness," Watling said.

The researchers said there are a number of actions drivers can take to avoid drowsy driving:

• Get enough sleep the night before a long drive.

• Take driving breaks.

• Pull over and take a 15- to 20-minute nap during a long trip.

• Drink a caffeinated beverage.

Many drivers believe that opening the car windows, turning up the radio or blasting the air conditioner will help them stay awake, but the researchers said these strategies do not help people stay alert.