Girls have a right to walk to their friends, or walk to shiurim, or walk to the nursing homes or wherever else it is they are going. As long as they arent just congregating in the street to “hang out” and to just be in the street I see no issue with it.
How do you know what they are up to unless you are busy paying attention to them and watching them during those “3 hours” that they are on the street.
I take it you are a boy so you should either be in a bais medrash learning or at home learning, or even sleeping. I see no reason why a boy may hang out on the street unless he has a reason to be there either.
If you were where you were supposed to be and doing what you were supposed to do this “enormous issue” wouldnt be a problem for you.