On highways divided into separate roadways as provided in RCW 46.61.150 and highways with three or more marked traffic lanes, public school district bus routes and private school bus routes shall serve each side of the highway so that students do not have to cross the highway, unless there is a traffic control signal as defined in RCW 46.04.600 or an adult crossing guard within three hundred feet of the bus stop to assist students while crossing such multiple-lane highways.