Where in the back seat should the infant car seat be placed (actually it is a convertible car seat for my 1-year-old). I was always told in the middle of the back seat, since that would protect them from a side impact accident (the car does not have side air bags) but I just read that head on collisions are more prevalent. Does this pose a risk being in the middle of the back seat?
You are correct that rear-facing in the middle of the back seat is considered to be the safest spot for infants to ride in cars, assuming, of course, that the car seat can be safely and correctly installed in that position. You just always need to make very sure that this is actually the case for your particular vehicle and car seat.
As for your concern about head-on collisions, what you have read is correct: a majority of crashes are frontal collisions. That said, you should be reassured to know that having an infant properly secured in a rear-facing car seat in the middle of the back seat actually stands to protect him better, rather than pose an increased risk. This is because in a frontal collision, when the front of a car makes impact, everything (and everyone) else in the car continues to move towards the point of impact until something stops them. For younger children who have graduated from rear-facing to forward-facing, their car seats' internal 5-point harness is what helps hold them back and keep them safely restrained in their seats. For rear-facing infants, the responsibility for stopping forward motion in a crash falls upon the entire shell of the car seat, which is positioned behind the infant such that the crash forces are distributed along the entire back of an infant's body as it is pushed into the protective infant car seat. This even distribution of forces over a greater area of an infant's body significantly reduces the likelihood of serious injury.
Since you asked about side-impact crash protection as well, I will also point out that while just under 25 percent of crashes are estimated to involve side impacts, this type of crash poses the highest likelihood of injury and/or death if for no other reason than because passengers have very little if any protection or distance between them and the point of impact. When it comes to minimizing these more "potent" crash forces, the middle of the back seat provides the greatest distance from either side of the vehicle. The side impact crash protection features now found on many newer car seats are also aimed at diffusing and minimizing side impact crash forces as much as possible.