Motor cycles are single-track two wheeled motor vehicle. They have become a common means of transport and they are quite fast just like a motor vehicle. They are also affordable and most people who do not have cars have them. Due to the high speed that they travel in, they are more prone to road accidents than automobiles. The other reason is that they are driven in the same road as vehicles and they are less noticeable and therefore are knocked down fast.
Some beginner riders constantly watch the road behind them, or fixate on their rearview mirrors, as if expecting Interpol to be chasing them. This comes at the expense of watching what's ahead, and usually stems from the falsehood that General Motors owns the highway and a mere bicycle can only trespass upon it if it dives onto the shoulder whenever an overtaking car approaches. A better idea: buy a LED blinker, and don't sweat it.