Interstate 270 (I-270) is a auxiliary Interstate Highway in the U.S. state of Maryland that travels from I-495 (Capital Beltway) just north of Bethesda in Montgomery County north to I-70 in the city of Frederick in Frederick County. It consists of the mainline as well as a spur that provides access to and from southbound I-495. I-270 is known as the Washington National Pike, and makes up the easternmost stretch of the Dwight D. Eisenhower Highway. Most of the southern part of the route in Montgomery County passes through suburban areas around Rockville and Gaithersburg that are home to many biotech firms. This portion of I-270 is up to 12 lanes wide and consists of a local–express lane configuration as well as high-occupancy vehicle lanes (HOV lanes) that are in operation during peak travel times. North of the Gaithersburg area, the road continues through the northern part of Montgomery County, passing Germantown and Clarksburg as a six- to eight-lane highway with an HOV lane in the northbound direction only. North of here, I-270 continues through rural areas into Frederick County and toward the city of Frederick as a four-lane freeway.
The freeway was built between 1953 and 1960 as the Washington National Pike between Bethesda and Frederick and carried U.S. Route 240 (US 240), which was rerouted off what is now Maryland Route 355 (MD 355) between these two points. With the creation of the Interstate Highway System a few years later, the road was designated as I-70S along with US 240. There were plans to extend I-70S to I-95 in Washington, D.C., on the North Central Freeway from the Capital Beltway; however, they were canceled in the 1970s due to opposition from residents in the freeway's path. The concurrent US 240 designation was removed in 1972 and I-70S became I-270 in 1975. Increasing traffic levels led to a $200-million (equivalent to $ in ) widening of the road in Montgomery County to its current configuration. Many improvements are slated for I-270, including the widening of the route that would add high-occupancy toll lanes (HOT lanes).
Route description
I-270 heads northwest from an interchange with I-495 (Capital Beltway) and MD 355 (Rockville Pike) in suburban Bethesda, Montgomery County, as a six-lane freeway. The left lane on each side is used as an HOV lane for carpools with two or more people in the northbound direction between 3:30 and 6:30 pm on weekdays and in the southbound direction between 6:00 and 9:00 am on weekdays. At the southern terminus, I-270 only has access to and from the eastbound direction of I-495. The road turns west and comes to an interchange with MD 187 (Old Georgetown Road) and Rockledge Drive (unsigned MD 187B). From there, I-270 continues west as a 10-lane freeway and merges with I-270 Spur, which provides access to and from southbound I-495. Past this interchange, I-270 continues north as a 12-lane freeway with an HOV lane and five travel lanes in each direction. The route passes through wooded suburban areas, where, prior to the cloverleaf interchange with Montrose Road (unsigned MD 927), I-270 takes on a local–express lane configuration with the outer two lanes serving as local lanes and the inner three lanes and the HOV lane serving as express lanes. Past Montrose Road, I-270 continues north into the Rockville area, turning northwest before it comes to a single-point urban interchange with MD 189 (Falls Road), where the highway sees 253,620 vehicles daily. The road continues to a modified cloverleaf interchange with MD 28 (Montgomery Avenue). Past MD 28, the freeway passes numerous business parks and some wooded areas before coming to an interchange with Shady Grove Road.