How safe are greyhound buses? Is it safe for a teenage girl to travel alone on a bus?

NOT SAFE! I took a Greyhound bus trip once and it was a nightmare! Some weirdo pulled a knife on me (luckily he didn't stab me!!!!) and when we came to a stop I had to alert the driver, who called the police and the guy was removed from the bus. To this day I don't know why he did it or why he chose to then leave me alone. All I know, is that I WILL NEVER RIDE A BUS AGAIN! It's cheap travel so the you see some pretty troubled people on buses.