I just read through a research paper from the Washington State Department of Transportation (WSDOT) that looked at the safety effects of putting a rumble strip down the centerline of two lane highways. WSDOT started aggressively installing these rumble strips down the middle of their two lane roads in 2004 and have enough/before after data to be able to draw statistically valid conclusions.
Minnesota uses rumble strips a lot on shoulders, but isn't as aggressive with putting them down the middle of the road. The research found very significant crash reductions in crashes where motorists cross over the centerline into oncoming traffic. These types of crashes were cut almost in half on roads that have the rumble strips.
Of course there is no magic solution when it comes to safety, but these rumble strips should probably be considered whenever undivided high speed roads are reconstructed. The report recommended they are especially effective on two lane roads that have less than 8,000 cars per day, a 45 to 55 mph speed limit, and narrow shoulders.
The research found the rumble strips to be great at reducing crashes where people doze off and start swerving. They're also effective in combating distracted driving. In the age of texting and driving, rumble strips seem like an effective countermeasure.