A downed utility pole in Jamesport closed Route 25, also known as Main Road, in both directions between Herricks and Manor lanes for more than six hours early Thursday, Riverhead Town Police said.
Police said the pole came down after being hit by a vehicle at about 3 a.m. No injuries were reported.
The state Department of Transporation website, informny.com, said the road was reopened shortly before 9:30 a.m.
All traffic was diverted north to Sound Avenue or south to Peconic Bay Boulevard during the morning commute.
PSEG Long Island spokeswoman Elizabeth Flagler said she expected that repairs could take "quite some time," partly because the damaged pole needed to be replaced.