Like a couple others have pointed out, I have been put in perilous circumstances by all kinds of vehicles, none excluded. Mostly I watch out for any erratic or aggressive driving. I also listen for vehicles behind me and how hard the engines are running and how close they are (in addition to my mirror). Maybe some of the more aggressive drivers have been Yellow Cab, mostly in the summer when the tourists are out. Then it would be full-sized trucks (construction workers) followed by larger vans (delivery, carpool, smaller buses). In all my experience the scariest drivers have been middle-aged men, period.