I would say all the above except for motorcycles.
Tailgating is far the most dangerous,and rubber necking also causes other mishaps.people on sail phones say they are not dangerous, thats a laugh. I work close to a very busy highway 19 & 41 here in Ga.
Traffic is always crowded on this highway.The Police Training Building is Right next door to me.I here them discussing the accidents that occur and 65% ofthe rearenders are caused by people dring to fast and talking on cell phones. Another 10% is buy big rig drives that are going to fast. and the rest is just plain uncall far.
CBTaters

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic