Analysis of information sources in references of the Wikipedia article "State highways in Washington" in English language version.
there are two state highway crossings at Blaine, and the four non-state highway crossings are at Boundary (former State Route 251), Ferry, Nighthawk, and Point Roberts.
Driving on ocean beaches—Driving is allowed on ocean beaches in Grays Harbor and Pacific counties. The beach is considered a state highway so all road, vehicle registration, and driver licensing regulations apply. The speed limit is 25 mph (40 km/h) and pedestrians have the right-of-way at all times. You may only enter the beach with your vehicle through marked beach approaches and you may only drive on hard-packed sand. Watch for beach closure signs and signs that occasionally prohibit beach driving.