Maryland has 16 Interstate highways, including six primary Interstates and ten auxiliary Interstates. The longest Interstate in Maryland is Interstate 95, while the shortest Interstate is I-295. Maryland also contains an unsigned Interstate, I-595; a former Interstate, I-170; and an intracounty Interstate, I-97, which is also the shortest primary highway in the Interstate Highway System.
Maryland has 14 U.S. Highways, including seven primary U.S. Highways and seven auxiliary U.S. highways. The longest U.S. highway in Maryland is U.S. Route 40, while the shortest U.S. highway is US 522. Maryland also contains six former U.S. highways.
Maryland has a unitary system of numbered state highways with numbers between 2 and 999. The longest Maryland state highway is Maryland Route 2, while several state highways are less than 0.5 mi (0.80 km) in length. Most of the shortest highways are unsigned. Several state highways have multiple disjoint segments that are denoted internally by suffixes, encompassing either old alignments of a major highway or a collection of service roads related to a particular highway.
Other systems
There are other systems of highways in Maryland that are not marked but are numbered internally.
County highways: All 23 counties have internal numerical designations for all highways under their jurisdiction.
Municipal highways: Every city, town, and village maintains an internal system of numerically designated municipal streets.
State reservation highways: Highways maintained by non-highways agencies of the state of Maryland. Examples of highways within this categories include streets on state university campuses, access roads to state parks and state forests, and highways within state-owned airports.
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).
Other agencies
All U.S. and state highways and I-83 within Baltimore are maintained by the Baltimore City Department of Transportation. Portions of U.S. and state highways within particular cities and towns are maintained by the respective municipalities.