first of all, you also have to keep in mind that thrash metal and hard rock is just as likely to "affect your mood adversely". and honestly, ANY kind of music that's so loud that it impairs the driver's ability to hear what's going on around them is dangerous, not just rap.
secondly, i feel like these statistics are meaningless. it all comes down to how much confidence you have in your driving ability and how much self-control you have. i, for one, am not going to stop listening to Eminem when I'm driving because statistics "show" that i'm more likely to get into an accident.
thirdly, your last statement? "young male drivers are the target group least likely to listen to road safety advice"? that is a SWEEPING generalization that doesn't take into account the facts that a) young female drivers present just as many problems when they're texting while driving or bopping around to Taylor Swift without bothering to keep their hands on the wheel, and b) we've got just as many middle-aged, so-called "conscientious" adults who put on makeup or talk on the phone when they're driving, regardless of the fact that they have been warned not to do so and hell, just plain, regular COMMON SENSE.