I recently was linked to Car Seats as Contraception, which argues that car seat laws have led to parents choosing to have fewer children because "physical limitations of many cars precludes the use of three car seats in the back seat." Now, this is a correlational study, so I'm skeptical that this is a real effect, but the premise here is also strange. If the only way to have three children in your car was to buy a larger car, I see why that could be a major issue for a lot of people. On the other hand, buying a narrow car seat is pretty straightforward, and three narrow seats fit across the back of almost anything.

We have several Cosco seats that are 17" wide. They are one of the cheapest seats out there ($50), and they fit three-across in almost anything. Manufacturers publish "rear shoulder room" measurements for their cars, so roughly we're talking about cars with at least 51". Alternatively, if you're willing to spend 4x as much ($200, still small compared to the cost of a car or of raising a child) there are 16" seats which would only need 48" across the back. Small cars I checked:

• Toyota Corolla: 52"
• Honda Fit: 53"
• Chevy Sonic: 53"
• Ford Focus: 54"
• Honda Civic: 55"
• Kia Forte: 55"
• Nissan Sentra: 55"
• Hyundai Elantra: 55"
• Subaru Impreza: 56"

Of these, I think we've put our seats three-across in both the Toyota Corolla and Honda Fit, the two smallest on the list, without issue. It's more annoying than just putting in two, but if you own your car (unlike us) you can leave them installed. There are tons of blog posts on this. This mild hassle doesn't seem like it could be large enough to cause a substantial shift in whether or when people choose to have a third child?