As St. Johns County continues to grow, so does the popularity of private and gated communities.  The idea is to add an extra layer of security for their residents, but privately owned roads can keep police from enforcing basic traffic infractions like speeding.  The St. Johns County Sheriff’s Office needs a written agreement to issue traffic citations in private communities. It’s up to the individual community to decide what level of enforcement they want, Sheriff’s Office spokesman Chuck Mulligan said.