The Maryland highway system consists of roads in the US state of Maryland that are maintained by the Maryland State Highway Administration (SHA). The three main systems of roads that comprise the Maryland highway system are Interstate Highways, US Highways, and Maryland state highways. Other roads in Maryland are maintained by individual cities and counties.
Interstate Highways and US Highways are assigned at the national level. Interstate Highways are numbered in a grid—even-numbered routes are east–west routes (the lowest numbers are along Mexico and the Gulf of Mexico), and odd-numbered routes are north–south routes (with the lowest numbers along the Pacific Ocean). US Highways are also numbered in a grid—even numbered for east–west routes (with the lowest numbers along Canada) and odd numbered for north–south routes (with the lowest numbers along the Atlantic Ocean). For this reason, mainline (two-digit) Interstate Highways in Maryland all have numbers between 81 and 97 for north-south routes and between 68 and 70 for east-west routes. In addition, mainline US Highways all have numbers between 1 and 29 for north-south routes and between 40 and 50 for east-west routes. Three-digit Interstate and U.S. Highways, also known as "child routes," are branches off their main one- or two-digit "parents". The Interstate and US Highways are generally maintained by the SHA, with some toll roads maintained by the Maryland Transportation Authority (MdTA) and some roads maintained by municipalities, including most roads in the city of Baltimore. Interstate 95 (I-95) and U.S. Route 40 (US 40) are the longest examples in the state.
Maryland state highways are the other state highways maintained by the SHA. Some state highways are maintained by municipalities while the Maryland Route 200 (MD 200) toll road is maintained by the MdTA. All roads maintained by the SHA are assigned route numbers, ranging from through routes passing through multiple counties to minor service roads that are less than a mile long. Many of the shorter state highways are unsigned. Some routes consists of multiple segments with letter suffixes; these suffixes are unsigned with the exception of MD 835A. There are two geographical clusters for Maryland state highways. The first, ranging from 2 to 37, consists of longer intercounty routes, with 2 to 6 in Southern Maryland, 7 to 10 originally skipped, 12 to 21 on the Eastern Shore, and 22 to 37 running west from Central Maryland to Western Maryland. The second cluster consists of routes from 38 to 378, running across the state from Garrett County in the west to Worcester County in the east. Numbers above 378 are assigned randomly.
Maryland Route 23 (MD 23) is a state highway in the U.S. state of Maryland. The state highway runs 20.58 miles (33.12 km) from U.S. Route 1 (US 1) in Hickory north and west to the Pennsylvania state line near Norrisville, where the highway continues as Pennsylvania Route 24 (PA 24). MD 23 is an L-shaped highway in northwestern Harford County that consists of two major sections. Between US 1 and MD 165 in Jarrettsville, MD 23 is marked east–west along a two-lane controlled access road named East–West Highway. From MD 165 to the state line, the state highway is marked north–south along Norrisville Road, a rural two-lane highway that passes through the villages of Madonna and Shawsville. The two sections of MD 23 are connected by a short concurrency with MD 165. MD 23 from Hickory to Jarrettsville was one of the original state highways marked for improvement by the Maryland State Roads Commission in 1909 and one of the original state-numbered highways in 1927. The state road was constructed from Hickory to Jarrettsville and from Norrisville to the state line in the early to mid-1910s. The gaps between Jarrettsville and Shawsville and from Shawsville to Norrisville were filled in the early 1920s. East–West Highway was constructed in the early 1960s to replace the parallel Jarrettsville Road. MD 23's eastern terminus was moved to US 1's new bypass of Hickory in 2000.