A Vancouver woman was arrested Wednesday after allegedly assaulting another woman on the shoulder of southbound Interstate 5 near Main Street.Dawn M. Ongrung, 30, was booked into the Clark County Jail for suspicion of fourth-degree assault, domestic violence, said Kim Kapp, spokeswoman for the Vancouver Police Department.Passing motorists called 911 just after 11 a.m. Wednesday when they spotted two women wearing pajamas engaging in a physical altercation near a blue Nissan sedan, Washington State Patrol Trooper Will Finn said.The female driver was trying to restrain the female passenger, Finn said. When the passenger got out of the car, the driver then got out and shoved the passenger and punched her four or five times, Finn said.The name of the victim was not released by police, but Finn said the women are in a domestic partnership. Vancouver police took over the investigation. The same vehicle was seen driving erratically in Lewis County about 9:15 a.m. and passersby reported that the driver was possibly intoxicated, Finn said. Troopers responded but did not see the vehicle. A female was arrested after allegedly assaulting another female on the shoulder of southbound Interstate 5 near Main Street.