This is the 3789th most frequent Swedish word.
inträffar
"Occurs" or "happens."
In this context, 'inträffar' is used to describe the happening of an event (an accident) at a specific condition (when the road is slippery).
En olycka inträffar varje gång när det är halt på vägen.
An accident occurs every time the road is slippery.
Here, 'inträffar' denotes the usual occurrence or arrival of a natural phenomenon (heat) during a certain time period (June).
Värmen inträffar vanligtvis i juni i Sverige.
The heat usually occurs in June in Sweden.
In this example, 'inträffar' reflects the action of a significant event taking place (a treaty signing) within a defined scenario (the interaction of countries).