3-Across Car Seat Installation: What You Need to Know Share this article Print article Need to fit three across, or just two seats side-by-side? There are a some things to know when doing so! Here’s a few tips! Each car seat should be installed independently tight, with less than an inch of movement side-to-side and front-to-back at the belt path. Place forward-facing seats in a seating position with a tether anchor. Booster seats need more space on the buckle side to allow the child to buckle and unbuckle. Educate booster riders about making sure they are unbuckling their seat belt each time, and not accidentally unbuckling a harnessed seat next to them. Contact a local Child Passenger Safety Technician for assistance when having trouble. Have questions? Start a chat with our Customer Support team now!