Maryland Route 3 (MD 3), also part of Robert Crain Highway, is the designation given to the former alignment of U.S. Route 301 from Bowie, Maryland, USA, to Baltimore. It is named for Robert Crain of Baltimore.

The route is a direct continuation of the four-lane divided highway previously followed by US 301. North of MD 424, the median between the carriageways is up to 300 feet (91 m) in width; several fast-food restaurants occupy the median in this area. The route was upgraded to this format in its persona as US 301 in 1954.

The route is severely congested; attempts to bypass it with new routings have failed. One such routing would have been Interstate 297, a direct freeway link between Interstate 97 and US 50/US 301/I-595.

In the past, Crain Highway originally held the designation MD 3, then US 301, and it currently carries both of these designations on different sections.

Started in 1922, Crain Highway was a new road built by the Maryland State Road Commission and ran from Baltimore to Southern Maryland. It was completed in 1927. With the opening of the Potomac River Bridge in 1940 it was joined with U.S. Route 301. After the Chesapeake Bay Bridge was built in 1952, US 301, which at that time ran along the current alignment of MD 3, was rerouted along US 50, across the Bay Bridge, and north to Wilmington, Delaware, as a bypass around the Baltimore-Washington Metropolitan Area. Former US 301 north of US 50 was then given back the MD 3 designation. After the construction of Interstate 97, MD 3 was cut back to I-97/MD 32, which led to the oddity of Maryland Route 3 Business in Glen Burnie being completely orphaned from its parent route. Despite this, the route is still designated Business MD 3 as recently as 2011.

Route 3 runs from the US 50/US 301 interchange (the western end of the US 50/301 concurrency) to an interchange with Interstate 97. Business MD 3 begins 9 miles (14 km) north of MD 3's northern terminus along Interstate 97 and runs through Glen Burnie.

Maryland Route 3 Business is a 5.1-mile (8.2 km) thoroughfare through Glen Burnie, Maryland and is the northernmost part of the Robert Crain Highway. Maryland Business 3 starts at the Governor Ritchie Highway (Maryland Route 2) and continues south into Southgate and then ends officially at Interstate 97 where it becomes New Cut Road and the Business Route 3 designation is discontinued. Business Route 3 is the only Maryland state highway that no longer connects with its parent route. The reason behind that is because its parent route, Maryland Route 3, used to have the right of way where Interstate 97 currently is. Now MD 3 ends 3 miles (4.8 km) south of Business Route 3's junction with Interstate 97. Robert Crain Highway is also the names of Maryland Route 3 between Millersville and Bowie and after Route 3 terminates at U.S. Route 301 in Bowie, southbound US 301 continues as that name until it reaches the Governor Harry W. Nice Memorial Bridge that crosses the Potomac River into Dahlgren, Virginia.

Maryland Route 3 Truck is an unsigned designation given to Pratt Street eastbound and Lombard Street westbound in downtown Baltimore, running from MD 295 (Paca Street/Greene Street) east to President Street. The route exists despite not connecting to the current alignment of MD 3.