How can I make the car safe for my 9-month-old?

Rear-facing car seat. Your baby should be in a rear-facing car seat until s/he is at least 1 year old and weighs 20 pounds.  make sure your child still meets the height and weight limits of your rear-facing car seat.  carefully follow the manufacturer's instructions when installing new or converting old car seats for your child.
Just wondering why? I believe that you are pediatrician? Just wondering why you are posting that question on this website?