I remember back in elementary/grade school everyone either road a bike or walked to school, many walking over a mile.
Now no child walks to school, in fact I am sure if a school found out a child was walking to school alone they would complain.
What happen?
What happened?
Well, a number of things.
When I was a kid I walked or rode a bike to school often. But I couldn't anymore. I suppose my answer is strongly influenced by my age and where I grew up.
In some places I couldn't really ride my bike on the road because it was too busy and there were no sidewalks. However, I could ride through the woods behind my house until I got to the next neighborhood and then ride on their streets until I reached the woods on the following side and continue on to school.
There are no woods now, no empty lots etc. No real way to ride a bike. Can't ride through everyone yards even if you wanted to, too many fences etc. So, kids get driven to school.
At another place the roads were gravel. I.e., few cars and they were going pretty slow. You can also hear a car on gravel about half mile away. So, it wasn't dangerous at all. Now those gravel roads are paved with a ton of fast moving traffic and no sidewalks. So, kids get driven to school.
I don't even need to consider the 'danger' from nuts etc., there's just no feasible way to do it.
Fern