Your son, as well as any child who is 10 thru 18 feels that they are 'big enough' to do what Actual ADULTS do.
The reality is, that children are so 'smart' because they learn to MIMIC adults' walk and talk, and they pick up everything they see on television.
A person DOESN'T mature as a human being until they become RESPONSIBLE. That means doing the right thing, and the "smart" thing any time they are faced with a choice.
Some people NEVER mature mentally, even though they may mature physically in their early teens. (!)
If you don't trust this world to leave your child alone, then have him or her walk with a friend, or drop him or her at a friend's house and pick him or her up when it's time to go get them.
Parents have to get to know their children's friends' parents too.
And as a precaution... there are walkie-talkies that are affordable, and you only have to pay for them ONCE. Not like a cell phone.
Keep in contact with your child, and the more you get to know their habits, the better you will feel about them when they you are not with them.