At each grade crossing where, because of the conditions surrounding it, the reasonable protection to life and property necessitates placing additional warning signs on the highway farther from the crossing than the home crossing signs, approach warning signs must be installed. The commissioner may designate grade crossings requiring additional signs on either or both sides of the crossing. Upon designating a crossing as requiring additional protection, the commissioner shall notify the road authority having the care of the highway. The road authority, within 30 days after notification, shall furnish and maintain uniform signs in the appropriate places on the highway on either or both sides of the grade crossings.