Disregarding just being teenagers (using their phones, doing burnouts), not having a proper driver's license (usually a 20+ lesson affair in Sweden) and driving old cars without safety systems; driving at less than half the speed of regular traffic in a smaller city or a more rural area means a lot of dangerous overtaking as the standard road is one lane in each direction (especially where the terrain doesn't allow for much more) and these cars are not allowed on highways. Since you are allowed to choose high school in Sweden, some choose one further away and driving. Making such roads congested.
It's normal cars regulated as tractors, because at some point it was considered useful to use cars as tractors. But as you can now convert them electronically, they are used at scale for convenience. So it like driving behind a tractor, but there are many tractors going back and forth to school, the supermarket and friends in rush hour and on weekend. All day, every day. And the drivers are very overrepresented in not behaving well on the road.
