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. Past this interchange, I-270 leaves Rockville and heads into
Gaithersburg, where it intersects
I-370. This highway provides access to a
park and ride lot at the
Shady Grove station, which serves
Washington Metro's
Red Line, and
MD 200 (Intercounty Connector), which heads east to
I-95 in
Laurel. Past I-370, the local lane configuration ends in the southbound direction, which now has an HOV lane and four travel lanes while the northbound direction still has an HOV lane, three express lanes, and two local lanes. I-270 continues past more suburban development before coming to a northbound exit and southbound entrance with
MD 117 (West Diamond Avenue). Past this interchange, the southbound HOV restrictions end and I-270 continues north with four travel lanes in the southbound direction and an HOV lane, three express lanes, and two local lanes in the northbound direction before reaching
MD 124 (Quince Orchard Road). Past MD 124, the northbound local lanes continue to the
diamond interchange at Watkins Mill Road, after which they end. From there, I-270 heads northwest as an eight-lane freeway with four southbound lanes, an HOV lane, and three travel lanes northbound. It passes through wooded areas, leaving Gaithersburg and comes to an interchange with Middlebrook Road. The freeway narrows to six lanes again past at this interchange, with three lanes in each direction, including a northbound HOV lane. I-270 continues into the
Germantown area and interchanges with
MD 118 (Germantown Road). A short distance later, after passing by some business parks, I-270 comes to an interchange with
MD 27 (Ridge Road) and Father Hurley Boulevard. Past MD 27, I-270 heads into more rural areas of woods with some farm fields, paralleled by a set of
power lines. The road has an interchange with
MD 121 (Clarksburg Road) in
Clarksburg near the
Clarksburg Premium Outlets, and the northbound HOV restriction ends past this interchange, with I-270 continuing north as a four-lane freeway. The power lines stop paralleling the route, and it continues through more rural areas of woods and farms, running closely parallel to MD 355. The median widens, with trees in the middle, and I-270 has
weigh stations on both sides. The highway reaches
Hyattstown, where it has an interchange with
MD 109 (Old Hundred Road). A short distance past the MD 109 interchange, I-270 crosses into
Frederick County, continuing northwest through rural woodland and farmland. It reaches the
Urbana area, where the route has an interchange with
MD 80 (Fingerboard Road). The highway briefly runs along the east side of MD 80 past this interchange before continuing through agricultural areas. It features a
scenic overlook in the northbound direction as the road passes through
Monocacy National Battlefield, which was the site of the
Battle of Monocacy. I-270 eventually leaves the battlefield area and continues into the commercial outskirts of
Frederick. Here, the road reaches an interchange with
MD 85 (Buckeystown Pike) near the
Francis Scott Key Mall. I-270 continues through commercial areas before coming to its northern terminus at an interchange with
I-70 and
US 40 (Baltimore National Pike). Past this interchange, the freeway continues north as the Frederick Freeway, a part of US 40 that interchanges with
US 15 and
US 340 a short distance north of I-270’s northern terminus. ==History==