My kid, right now, is at the library.
He’s 12. He’s got a little cash, but no cell phone (he loses them madly). Also has cash to buy himself some lunch (he’s on school vacation at the moment, but has assignments to do.)
He’s in an urban area of Sydney. Granted, there’s just one long street between here and there, but it’s a pretty busy, crowded area even on a Tuesday afternoon. I’ve seen some strange people out and about.
I told him this: If you feel unsafe, get out of the way, go into a shop or a cafe or something until what ever is making you feel unsafe goes away. There’s payphones everywhere, you’ve memorised my numbers, call me if you need a little handholding, but other than that tell me about it when you get home.
If you feel frightened by another person (not just sort of mildly creeped out or sort of unsafe, but if someone is genuinely scaring you - like, trying to touch or grab you or something) YELL YOUR HEAD OFF. Scream and make a very public fuss - it’s a busy street, you’re obviously not an adult, someone will help you. If it turns out to be nothing, then you’re embarrassed, but nobody ever died of that. If it turns out to have been dangerous, you’ll be safe. Then call me.
If it’s raining, that’s why I bought you an umbrella, tough. 
I know when the library closes and how long it takes him to meander home looking at interesting things in shop windows. I trust him to buy and eat his own lunch, usually take away to the very very very interesting old cemetery near the library. (That’s ok with me, it’s a pretty historical, really nifty place and everybody needs a study break.)
He rides a public bus to and from school every day. He has demonstrated he can think on his feet - he and every other kid wearing his school’s uniform got kicked off the bus one day. Instead of walking home (same long busy street, just further up than he’s used to going) he had a mild panic, and ended up at a friend’s house. Tried to call me - stupid Mom forgot her cell phone and wasn’t at the office. I get home, he’s late, REALLY late. I have a panic attack thinking he’s dead or dismembered. I log onto my computer to get the police number - no good calling 000 if I don’t know if he’s in immediate danger, which starts up my e-mail, which gets me an e-mail that has a subject line from my kid which starts out:
HELP MOM PLEASE RESCUE ME PLEASE!!!
So, I go from panic attack to heart attack, LOL!
Long story short, he’s having cookies and pop at a friends house while the friend’s mom (bless her) keeps an eye on him. But smart move to try e-mail, since he knows my habits and knows most days I check my home e-mail from the office (I am not normally out of the office.)
So ok, he lost it a little by not just walking home, but he had a good recovery and we talked about, ok, this street? This is X street, if you stay on it, you will see the X pub, yeah? So then you know the street next to that is your street, right?
So it’s all good.
But I still worry, cause I’m his mom.
Oh, and the kid has Aspergers Syndrome, too. I let him do this stuff anyway, cause he has to learn to live with the rest of us. 
So in short, Marli, your kid will be fine, I had the same panic attack the first time I let him go to the library by himself (and I’ll have it again this weekend when I let him take the train alone for the first time to his Yu Gi Oh tournament.)
Cheers,
G