"We do see more accidents when the weather is bad, but the more serious accidents take place when the weather is good," Lennart Helsing at the Swedish Transport Administration (Trafikverket) told the TT news agency on Holy Thursday.
"The worst occur in spring and summer, and often on quite good roads."
The risk, he explained, came from motorists simply driving too fast on big roads when the sun is shining.
Easter holidays also pose a risk. Although there will be less traffic as a whole on Sweden's road, most people who do jump in the car are heading the same way - away from town.
Swedes are set to quit the cities in droves, either after work on Holy Thursday, or making an early run on Good Friday to join friends and family for Easter.
"That's when we see such extreme traffic," Helsing said.