Is public transportation good for our children?

While my kids grow up, some of my biggest worry's have been their friends and where they hang out. Years ago one of my sons used the bus system and then max; we promoted his adventuresome and self reliant outings.  Now years later I question that wisdom, the transit system exposed him to places and people he was too young to comprehend and deal with.  I may be wrong but I blame some of the troubles he worked through on my willingness to let him use public transportation.  His younger brother is approaching the age where we will have to let him make some of these same choices.  But I have already decided to not promote public transit.  It means I will continue to drive him places and meet some of his friends. That's OK