The OP is concerned about his/her safety while here in the USA. We can honestly say that our air travel and passenger rail networks are extremely safe, more so than at home. We most likely have a higher crime rate than at home, but it is generally limited to the ghettoes, and even then mostly to bad guys in the ghettoes. What the OP really needs to be careful about is the automobile. Either as a pedestrian or more likely occupant of a car they are far more likely to get maimed or killed by an automobile than a bad guy, and all this advice on this string is doing the OP a disservice. As a matter of fact, I believe that for non-thugs Philly is safer overall than the American average, if (as I suspect) the OP is trying to avoid getting maimed or dying.