A man aged around 60 died following a collision between a bus and a car near Varberg. Another man aged around 60 lost his life in Mellerud municipality, as did a woman aged around 60 on the island of Tjörn.
"It hasn't dropped below freezing point just yet, but several of our patrols have reported this evening that roads are slippery out there in the west region," police spokesperson Johan Håkansson told the TT newswire on Monday evening.
"That is not to say that slippery conditions were a factor in the serious accidents we unfortunately had this afternoon, but it serves as a reminder of how quickly things can go wrong on the roads. With that in mind, there is every reason to drive with caution."
The warning of slippery roads on Tuesday morning applied specifically to the Gävleborg, Uppsala and Västmanland regions, but it could be icy elsewhere as well.
As early as Friday, the Swedish Transport Administration warned that there is an increasing risk of black ice in western Sweden.
"Black ice, also known as flash ice, is extremely treacherous because it is usually invisible, yet makes the road surface exceptionally slick. It often forms when the road surface is cold and damp at temperatures around 0C. It typically becomes slippery late in the evening or early in the morning when temperatures drop," the agency wrote on its website.
Particularly vulnerable spots include bridges, overpasses, areas near bodies of water, and shaded patches along the roadside.
There were also two fatal traffic accidents in the southern region of Skåne on Monday. A man aged around 70 died following a crash on the E6 motorway north of Ängelholm, and a woman aged around 20 died in a collision with a truck outside Åstorp.