The Columbian reports that a 911 caller apparently mistook the sword for a gun.
Troopers, Vancouver police and Clark County sheriff's officers rushed to the scene, turned on their spotlights and talked to the man over a loudspeaker with guns drawn.
Trooper Will Finn says when officers are told someone has a weapon, "we approach as if someone is indeed carrying a weapon."
The 20-year-old man said he was headed home to Elma, Wash. Police drove the man to a relative's house in nearby Vancouver and warned him that pedestrians aren't allowed on I-5.
The newspaper says the shutdown lasted about five minutes.