Formerly, reference location signs, aka milepost, mile marker or MM, is a varying sized green sign identifying the distance from the beginning of the interstate in each state. Mile markers assist road users in estimating their progress, provide a means for identifying the location of emergency incidents and traffic crashes and aid in highway maintenance and servicing. Where the Interstate route intersects a state line, milepost numbering typically begins at zero. The numbers then increase as you travel north on north-south roadways and east on east-west roadways. Exit numbers often mirror these numbers where roadways intersect.

Mile Marker illustration

Illustration: Mile Marker along the roadway.

 

Mile Marker photo

Photograph: Actual Mile Marker along an interstate roadway.