It costs about $3,000 per mile to mow down the weeds while herbicide spraying costs about $140 a mile. Only 45 miles of road was mowed last year, leaving roadways plagued with overgrown weeds. Guess where these weeds grow? Yep, into the edges of the roads and beyond, exactly where I want to ride my bicycle. Along some roads, the weeds are so high you can't see down the road.