Slow drivers are the ones that don't like to speed because there afraid of getting caught or those who simply rather not put all there attention on the road. Slow drivers generally don't create a serious problem because they only go 10-15 mph under the fastest safe driving speed for the road (not the speed limit!). However, if you are in a rush they can be very annoying. Slow drivers unfortunately keep the people behind them driving at there speed. Making up 10 to 20 percent of the drivers on the road, they generally dictate the general traffic speed when there is moderate traffic and therefore in my view the 85th percentile speed of the road.