All three types of highways together provide access to all incorporated and unincorporated areas in all 23 counties of Maryland as well as the independent city of Baltimore.

There are other systems of highways in Maryland that are not marked but are numbered internally.

The vast majority of Interstate, U.S., and state highways are constructed by and maintained by the Maryland State Highway Administration (MDSHA).

All toll facilities in the state and limited access highways within Baltimore except I-83 are constructed and maintained by the Maryland Transportation Authority (MdTA).

Portions of U.S. and state highways within particular cities and towns are maintained by the respective municipalities.