They make no mention of much better driver training; higher-quality and routinely inspected automobiles; less traffic; and cultural values that probably play a huge role.
Wikipedia says Swedish drivers can't get a fully-privileged license until they're 20 or 21. Compare that to the U.S. where in many states a 16 year old who took a single practical driving test is considered fully qualified. I wonder how much of a difference that makes.
Less than you might think. Studies have consistently shown that experience matters much more than age. Though holding experience constant 17 year olds are more likely to get in accidents than 22 year olds, an 18 year old with two years of driving experience is much less likely to get into an accident than a 25 year old with 1 year of driving experience.
Furthermore, accident rates start increasing with age at only the mid 20's, perhaps due to decreasing reaction time with age.
The very first time I drove alone after getting my license, I was backing out of my parents' driveway and managed to put huge scrapes in three cars because I didn't have a strong enough understanding of how the world worked in reverse.
Because all three cars were ours, and it occurred on our property, there were no tickets, no police activity, no DMV penalties, nothing -- if my parents hadn't been strict (and thank GOD they were), I could've just kept driving.
I also cringe at the thought of that happening, because I, like a lot of 16 year olds, was really stupid.
My parents had me drive a VW station wagon with a Bug engine, automatic transmission and AC. I think I could walk faster. I think the only ticket I could get was for going too slow.