Interstate 895 (I-895) is an Interstate Highway in the U.S. state of Maryland. Known as the Harbor Tunnel Thruway, the highway runs 14.87 miles (23.93 km) between one junction with I-95 in Elkridge and another interchange with I-95 on the east side of Baltimore. I-895 is a toll road that crosses the Patapsco River estuary via the Baltimore Harbor Tunnel, connecting U.S. Route 1 (US 1), I-695, and the Baltimore–Washington Parkway in the southwestern suburbs of Baltimore with US 40 on the east side of Baltimore. In conjunction with a pair of spurs, unsigned I-895A and I-895B, I-895 provides access to the tunnel from I-97 and Maryland Route 2 (MD 2) in Glen Burnie. The highway is designed for through traffic by having partial interchanges that require vehicles from almost all starting points to pass through the tunnel and the tunnel toll plaza, where a $3 toll is charged to passenger vehicles, before exiting the facility. I-895 and its spurs are maintained by the Maryland Transportation Authority (MdTA) and are a part of the National Highway System for their entire length except for the part of I-895B between MD 2 and I-895A.

The idea of a crossing of the Patapsco River south of downtown Baltimore has been studied since the 1930s. In the early 1950s, the Maryland State Roads Commission chose to construct a four-lane tunnel between the Canton and Fairfield neighborhoods of Baltimore and approach highways to connect the tunnel with major highways to Washington, Annapolis, Richmond, and Philadelphia. The tunnel and approach highways were constructed beginning in 1955 and opened in November 1957, opening a bottleneck for Baltimore through traffic, which formerly had to navigate the city streets. The Harbor Tunnel Thruway was connected with the John F. Kennedy Memorial Highway in the early 1960s and the portion of I-95 south to Washington in the early 1970s. With these connections, I-895 was burdened with most of the through traffic passing through Baltimore. The congestion was not resolved until I-95 through Baltimore was completed when the eight-lane Fort McHenry Tunnel opened in November 1985. The transfer of most traffic to the new tunnel allowed the Baltimore Harbor Tunnel to be partially shut down for extensive maintenance in the late 1980s.

I-895 begins at Exit 46 of I-95 in Elkridge with single-lane ramps from I-95 north to I-895 north and I-895 south to I-95 south. The highway, which has a speed limit of 65 miles per hour (105 km/h), expands to four lanes on a viaduct over local roads and CSX's Capital Subdivision and MARC's Camden Line. I-895 crosses the Patapsco River and US 1 (Washington Boulevard), then receives the ramps from Exit 1 with US 1 south before passing under I-195 with no access. I-895 continues east with a wide grass median and parallels the Patapsco River and a pair of transmission lines. The highway passes several industrial facilities in Halethorpe as it crosses the Amtrak Northeast Corridor and MARC's Penn Line and Herbert Run. I-895 meets I-695 (Baltimore Beltway) at Exit 3, then crosses Hammonds Ferry Road in Baltimore Highlands before Exit 4 with MD 295 (Baltimore–Washington Parkway), where the speed limit drops to 55 miles per hour (89 km/h). The wide median reduces to a Jersey barrier as the highway crosses MD 648 (Annapolis Road).

I-895 crosses marshland, the main line of the Baltimore Light Rail, and the Patapsco River and curves to the northeast at Exit 6 for the southern approach, unsigned I-895B, in Brooklyn Park. The highway enters the city of Baltimore and curves to the east over Patapsco Avenue before Exit 7 with MD 2 (Potee Street). I-895 parallels CSX's Curtis Bay Branch as the highway passes between an industrial area to the north and the Brooklyn neighborhood. The highway crosses the Curtis Bay Branch on a steel truss bridge ahead of Exit 8A with Shell Road, which heads toward the Curtis Bay, Baltimore neighborhood, and Exit 8B with Frankfurst Avenue, which leads to Hanover Street and downtown Baltimore. I-895 passes through the 14-booth toll plaza for the tunnel, then receives exit ramps for Exit 9 with Childs Street. The speed limit decreases to 50 miles per hour (80 km/h) as the highway curves to the northeast through the Fairfield unit of the Port of Baltimore and descends into the Baltimore Harbor Tunnel.

I-895 surfaces from the tunnel adjacent to the toll plaza for the Fort McHenry Tunnel within the Canton neighborhood. The highway passes over several rail lines, then the Exit 10 ramp to Holabird Avenue diverges from I-895 north immediately before passing under I-95 (sharing no access with that Interstate). Now running north, as I-895 returns to ground level, the highway crosses Ponca and Boston streets; the speed limit increases to 55 miles per hour (89 km/h) ahead of exits 11A-B, Boston and O'Donnell streets, respectively. The highway crosses a rail line before passing through the Riverside neighborhood in a cut. I-895 passes under MD 150 (Eastern Avenue) ahead of Exit 12, a full interchange with Lombard Street just to the west of Johns Hopkins Bayview Medical Center. The highway turns northeast and crosses both the Amtrak Northeast Corridor and CSX's Philadelphia Subdivision before Exit 13 with US 40 (Pulaski Highway) and MD 151 (Erdman Avenue). After crossing Herring Creek, I-895 meets Moravia Road at Exit 14. The highway crosses Moores Run before reaching its northern terminus at Exit 62 of I-95 (John F. Kennedy Memorial Highway) just west of the Baltimore city limits, with ramps from I-895 north to I-95 north and I-95 south to I-895 south.

In 1938, the Maryland State Roads Commission (SRC) commissioned an engineering study titled Maryland's Primary Bridge Program to examine the feasibility of major bridges across significant transportation barriers, including a bridge crossing the Patapsco River southeast of the Inner Harbor. Another study in 1944 examined the idea of a bridge with limited-access approach roads running from US 1 in Elkridge to the Patapsco River crossing and from the bridge to US 40 near Erdman Avenue in east Baltimore. The financial resources for the project were established in 1947 when the Maryland General Assembly passed an act allowing for the pooling of revenue bonds and toll receipts between the state's toll facilities—the existing Potomac River Bridge and Susquehanna River Bridge, and the upcoming Chesapeake Bay Bridge—to finance the construction of the Patapsco River Crossing. Finally, a 1953 study examined three different routes—Canton-Fairfield, Canton-Fort McHenry, and a Canton-Fort McHenry-Fairfield dual crossing option—and whether the crossing should be a bridge or tunnel.

In 1954, the SRC decided to construct a tunnel between Canton and Fairfield, with three approach highways: a west approach from US 1 in Elkridge, a south approach from MD 2 in Glen Burnie to connect with the west approach in Brooklyn Park, and a north approach from US 40 and Erdman Avenue in east Baltimore. The approach highways were to be limited-access with directional, partial interchanges so that only traffic intending to use the tunnel would use the approach roads. Any vehicles entering an approach road would not be able to exit until having passed through the tunnel and the tunnel toll facility.

Shortly after work began on the Patapsco Tunnel Project on April 7, 1955, several changes were made to the plans for the approach highways. The northern terminus at US 40 was altered to allow an extension from US 40 to the southern end of the future Northeastern Expressway (now John F. Kennedy Memorial Highway). As a result, additional connections with US 40 were planned for the area around present day Exit 14. In addition, the south approach was to have a tie-in to the Glen Burnie Bypass (now I-97) then under construction. The tunnel and approach highways were completed and opened November 29, 1957 as the Baltimore Harbor Tunnel and the Harbor Tunnel Thruway, respectively. The opening of the tunnel and approach roads removed a significant amount of traffic from the streets of Baltimore and eliminated 51 traffic lights from the route of motorists passing through the city.

The Harbor Tunnel Thruway was extended north to the city limits of Baltimore to seamlessly connect with the Northeastern Expressway when that highway opened northeast to the Baltimore Beltway in 1961. In 1969, Moravia Road was extended east to US 40 using the connector between US 40 and the thruway and several ramps were added to that road's interchanges with US 40 and the thruway. In addition, flyover ramps were constructed at the city limits for I-95 to diverge from the John F. Kennedy Memorial Highway onto its own path through east Baltimore in 1970. The Harbor Tunnel Thruway was extended at its south end in 1973 to connect with I-95 shortly after that Interstate was completed between the Capital Beltway and the Baltimore Beltway in 1971.

Since I-95 had not yet been completed through Baltimore, the Harbor Tunnel Thruway, which was designated I-895 in 1979, was the main route for traffic passing through Baltimore. As a result, the highway was very congested, and travel through Baltimore had once again become a bottleneck. Relief came with the completion of the eight-lane Fort McHenry Tunnel on I-95 on November 23, 1985. With most traffic diverted to the new tunnel, major reconstruction work began on the Baltimore Harbor Tunnel. Traffic was reduced to one lane in each direction through the tunnel as each of the two tubes was renovated between 1987 and 1989. More recent changes include the elimination of the entrance ramp from Ponca Street at Exit 10, the expansion of Exit 12 to a full interchange to provide access to Johns Hopkins Bayview Medical Center in both directions, and the reconstruction of the northern interchange with I-95 in 2009 so I-895 enters and exits I-95 on the right side of the roadway.

The original toll for the Harbor Tunnel Thruway was 40 cents for passenger vehicles and 85 cents for trucks. By 1985, the toll had risen to $1. Electronic toll collection began at the toll plaza in 1999 for M-TAG customers; the M-TAG system was absorbed by E-ZPass in 2001. MdTA increased the toll for passenger vehicles to $2 in 2003. In May 2011, the agency announced the toll for the Harbor Tunnel Thruway and the two other harbor crossings would increase to $3 on October 1, 2011 and to $4 on July 1, 2013.

The Harbor Tunnel Thruway has had three different exit number systems throughout its existence. The first numbering scheme was in place by 1963. The northbound exits were numbered between 1 (Holabird Avenue) and 5 (US 40), while the southbound exits were numbered 1 (Hanover Street) to 7 (US 1). The second numbering scheme, which did not change the interchange numbers on the northern approach to the tunnel, was introduced in 1971. The exits on the western approach were renumbered 11 (Hanover Street) to 17 (US 1). Under both schemes, the Childs Street exit did not have a number and the Moravia Road interchange was numbered as Exit 1 of the John F. Kennedy Memorial Highway. The third and present numbering scheme was enacted in 1991.

I-895 has two auxiliary routes, I-895A and I-895B. Both highways are portions of the southern approach to the Baltimore Harbor Tunnel that connects with the mainline of the Harbor Tunnel Thruway in Brooklyn Park.

I-895A is the designation for the 0.71-mile (1.14 km) connector between the northern end of I-97 just north of I-695 (Baltimore Beltway) and I-895B within Glen Burnie. The highway was constructed in 1957 to connect the northern end of the Glen Burnie Bypass with the Harbor Tunnel Thruway. In conjunction with the reconstruction of I-97's interchange with I-695, in which the loop ramp from I-97 north to I-695 west was replaced with a flyover joining I-695 on the left, a loop ramp was added on I-895A in 1995 to allow access to the right side of I-695 west for traffic exiting at MD 648 (Baltimore Annapolis Boulevard).

I-895B is the designation for the 2.67 mi (4.30 km) southern approach to the mainline of Harbor Tunnel Thruway between MD 2 (Governor Ritchie Highway) in Glen Burnie and I-895 in Brooklyn Park. The highway was completed in 1957 with the remainder of the Harbor Tunnel Thruway. The only change to the southern approach is the addition of ramps from I-895B north to I-695 west and from I-695 east to I-895B south to improve access between MD 2 and the Baltimore Beltway; these ramps, now marked as Exit 3A on I-695 east, were completed in 1968.