@iceray that can't be said of children.
Sure, kids are crazy, curious, and energetic. They sometimes fail to realize what they are doing may be bad. But that is where the parenting comes in. When I was a child, every time we got close to the road in preparation to cross it, I had to hold the hand of either my parent or babysitter. Children can be protected in a humane way!
Even if children running into the road was a legitimate reason for child leashes, why have I seen them everywhere BUT near the road? I see them mostly in shopping malls and in stores, where yes, a child may wander away from their parent, but once again, it is the parent's responsibility, and an easily accomplished one at that, to simply watch your child! If you're unable to simply keep an eye on your child, you should have thought a bit harder before having children.