"That's what happens. We're powerless. It's not that simple, to just go in and stop this," Stockholm policeman Anders Mattsson told news agency TT.
Streetracing is illegal in Sweden, but Mattsson said there wasn't much to be done.
Racers entered the E4 highway south of Stockholm and continued their antics early into Saturday morning. Several of the racers were previously unknown to police.
Racing took place in the areas of Hallunda, Fittja, and Slagsta as well, and traffic was stopped by illegal blockades on the highway as hundreds of spectators gathered.
No one was injured during the racing. Police said that they may present a whole slew of criminal charges if they are able to identify all of the racers and organizers – but that usually racers have vanished by the time police arrive at the scene.