Highways have markers to indicate directionality, to indicate distances to exits and to give drivers a point of reference when telling others where they are. Local, state and interstate highways have mile marker signs, which are generally small and green.
For most highways, mile marker numbers start at beginning of the highway in the southernmost state, and numbers increase as they go north. On interstates that run from east to west, mile markers generally start at the westernmost point and increase as drivers travel east. Mile markers are also linked to exit numbers, so that a driver who is at mile marker 37 is approximately 3 miles from exit 40. Mile markers help drivers indicate where they are when talking to people such as tow truck drivers, particularly in areas with few other landmarks.