Taller weeds are obstructing the view of the white reflective delineators that mark the edges of the road in some places.
Rune Karlsvärd from Motormännen, an organization for car drivers, told Swedish Radio in Östergötland that it is unacceptabel that not more is done to tackle the weeds, which he says pose a health and safety risk.
"This is a concern we have every year, and we always report it to traffic authorities. This year it's been a great summer for the weeds - it's rained a lot and there's been a lot of sun - it's practically caused a greenhouse effect", he says.
Karlsvärd says it is not just the edges of the road that are being hidden by the weeds - there's a higher risk of hitting a wild animal on the roads because of them.
"Deer can hide in the grass by the side of the roads. They could jump out into the roads, causing drivers to panic, break and swerve off the road. If you're able to see the side areas, it would be much better," he says.
But Jonas Bruce from the Swedish Transport Administration in the region says the situation on the E4 highway does not worry him.
"We've heard people's concerns over weeds getting in the way at intersections. But on a road like the E4, I absolutely don't see the weed growth as a problem for traffic safety", he says.