Interstate 270 Maryland
Overview
Interstate 270 in Maryland is a regional connector between the Capital Beltway (I-495) and I-70 at Frederick. A heavily traveled commuter route, I-270 joins Washington, D.C. with points west to Hagerstown and Cumberland and north into Pennsylvania.
Just north of the Capital Beltway, I-270 splits into two branches. The main line angles east to link with I-495 by Chevy Chase. Interstate 270 Spur drops south to join I-270 with I-495 ahead of Cabin John and the American Legion Memorial Bridge across the Potomac River.
North from the merge of I-270 and I-270 Spur, the freeway expands with four overall roadways. The Local / Express configuration extends north to Gaithersburg and MD 117 (Clopper Road) at Exit 10.
History
The freeway for Interstate 270 was concurrently signed with U.S. 240, an intrastate route from Frederick, Maryland to Washington, DC, from 1960 onward. Interstate 70S was established along the route in 1956 and I-270 subsequently applied to what is now I-270 Spur. I-70 east to Baltimore was designated Interstate 70N.
Interstate 270 was originally the connector joining I-495 with I-70S/U.S. 240 – 1968 Maryland Official Map
U.S. 240 was decommissioned with approval of the American Association of State Highway Officials (AASHO) on June 20, 1972. The Maryland State Highway Administration (MDSHA) determined that the motoring public was orientated to the I-70S signing and that U.S. 240 no longer served any useful purpose. MDSHA followed with a numbering plan to AASHO for approval to eliminate I-70S and I-70N on March 1, 1973:
We are requesting the consideration of the Route Numbering Committee and the concurrence of the Federal Highway Administration in the elimination of the Cardinal Direction suffix letters on Interstate Routes I-70S and I-70N.
It is our understanding that preliminary agreement was reached with Mr. Frank C. Turner, Federal Highway Administration, and
your office on the need for the renumbering of these routes to eliminate the postscripts nationwide. In light of this, it is requested that
the following route numbers be changed accordingly:I-70N to I-70 – From the junction of I-270 (formerly I-70S) southwest of Frederick easterly to the junction of I-95 in Baltimore City
I-70S to I-270 – From the junction of I-70 (formerly I-70N) southwest of Frederick, southeasterly to the junction of I-495 (Captital Beltway) at Pooks Hill
I-270 to I-470 – From the junction of I-270 (formerly I-70S) north of Democracy Blvd., southerly to the junction of I-495 (Capital Beltway)
Interstate 470 prematurely added to the Washington, DC inset on the 1975 Virginia Official Highway Map
The American Association of State Highway and Transportation Officials (AASHTO) Route Numbering Committee concurred with these requests at the meeting held in June 1973. However, in a letter dated February 11, 1974 from AASHTO to MDSHA, the matter of Interstate 470 was questioned:
There is a possibility that you will want to consider not changing the route number of existing I270 between I70S and I495 but rather handling this as a long connection to 270 and handle traffic by appropriate guide signs rather than having a separate interstate route number.
The U.S. Department of Transportation approved the numbering changes of I-70S as I-270 and I-70N as I-70 on March 18, 1975. The FHWA also concurred with the assessment of AASHTO regarding the proposal for Interstate 470:
We do not approve the renumbering of the existing I-270 as I-470 from its junction with I-495 near Bradley Boulevard northerly to a junction with former I-70S near Tuckerman Lane. Existing I-270 to I-495 and Northern Virginia points and the newly numbered I-270 to I-495 and points in Maryland will be considered a wye (Y) connection of I-270 with I-495.
I-270 Spur was instead established in place of the short I-270 on the west leg connecting with the Capital Beltway.
Route Information
North End – Frederick, MD
South End – Bethesda, MD
Mileage – 34.40
Cities – Rockville, Gaithersburg, Frederick
- Junctions –
Source: December 31, 2021 Interstate Route Log and Finders List
I-270 Annual Average Daily Traffic (AADT)
I-270 Spur Annual Average Daily Traffic (AADT)
| Location | Vehicles per day |
|---|---|
| I-495 to Exit 1 | 130,730 |
| Exit 1 to I-270 | 131,292 |
Interstate 70S defaulted onto U.S. 15 north in Frederick prior to the 1960s completion of the freeway west from Frederick to Hagerstown.
Button copy signs preceding the split of I-70/270 eastbound previously referenced Interstate 70S. 02/18/94
$27 million in roadwork improved Interstate 270 at MD 187 (Old Georgetown Road) and Rockledge Drive east of I-270 Spur. Work rebuilt the diamond interchange and widened the MD 187 overpass to ten lanes. The project also improved access to Rock Springs Industrial Park with two new ramps from I-270. Despite inclement weather, construction wrapped up nine months ahead of schedule on November 4, 2003.1
Highway Guides
North End 
– Frederick, Maryland
North at 
Traffic separates at the north end of I-270 into a two-lane ramp (Exit 32) for Interstate 70 and a two-lane continuation of the freeway to U.S. 40 west. 08/04/13
Exit 32 branches away from the I-270 mainline for I-70/U.S. 40 east to Baltimore and a left merge onto I-70 west toward Hagerstown. 08/04/13
Replaced with a small guide sign by 2012, an end shield for I-270 stands at the gore point where U.S. 40 merges from I-70 westbound. Photo by Tim Reichard (08/25/02).
East at
U.S. 15/340 combine along a freeway leading northeast to I-70 at Exit 52 B and U.S. 40 in the city of Frederick. 08/15/21
I-270 branches southeast from Interstate 70 at the ensuing exit beyond U.S. 15/340. 08/15/21
An older diagrammatic sign preceded the split of Interstate 270 south from I-70 east at Exit 53. Photo by Jeff Royston (06/10/06).
Ramps from U.S. 15/340 north and MD 180 add two auxiliary lanes to Interstate 70 east for Exit 53 and I-270 south to Washington, DC. 08/15/21
I-270 extends southeast from a freeway along U.S. 40 at Exit 53. U.S. 40 east combines with I-70 to Ellicott City as I-270 diverges southward to Gaithersburg and Rockville. 08/15/21
West at
I-70/U.S. 40 advance west from MD 355 (Market Street) south of Downtown Frederick to their split at I-270 (Exit 53). 06/08/12
Interstate 270 north ends at I-70, with U.S. 40 overtaking the freeway north to U.S. 15 (Frederick Freeway) to Gettysburg, Pennsylvania. 06/08/12
Replaced overheads one quarter mile from I-270 south. Photo taken by Tim Reichard (08/25/02).
Exit 53A loops away from I-70 west to Interstate 270 south toward Gaithersburg, Rockville and Washington, DC. 06/08/12
South End – Bethesda, Maryland
South at 
Interstate 270 concludes with ramps joining both the Capital Beltway east toward Silver Spring and MD 355 (Rockville Pike) south to Bethesda. 08/04/13
West at
One mile southeast of the wye interchange (Exit 35) separating I-270 north from I-495 west. 12/30/12
Exit 34 departs just ahead of I-270 for MD 355 (Rockville Pike). The state route parallels I-270 to the east, serving Rockville and Gaithersburg. 12/30/12
Westbound I-495 (Capital Beltway) at Exit 34 for MD 355. MD 355 follows the original course of U.S. 240, which was replaced by I-270 between Bethesda and Frederick. 12/30/12
Traffic partitions for I-270 north to Frederick from the Capital Beltway westbound below the Rockville Pike overpasses. I-495 winds westward 2.5 miles to a wye interchange with I-270 Spur. 12/30/12
Interstate 495 advances southwest to Northern Virginia while I-270 initially heads west to I-270 Spur and then northwest to Rockville and Frederick. 12/30/12
South at 
Southbound on Interstate 270 at the split with I-270 Spur. This is the lone reference on guide signs for the spur route. Photo by Jeff Royston (06/10/06).
North at
Interstate 495 splits with I-270 Spur 3.6 miles north of the American Legion Memorial Bridge spanning the Potomac River from Virginia. 12/21/12
The Capital Beltway northbound widens to six lanes ahead of the separation with Interstate 270 Spur. The left lane is restricted to HOV-2 traffic. 12/21/12
Interstate 270 Spur meets Democracy Boulevard by Westfield Montgomery Mall midway between the Capital Beltway and the merge with I-270 north. Interstate 270 expands with Local/Express roadways northward through the Rockville area. 12/21/12
Guide signs for I-270 Spur reference the route as Interstate 270. Mileposts along the freeway however reference the spur extension. 12/21/12
Sources:
- “State Highway Administration Celebrates Opening of I-270/MD 187 (Old Georgetown Road)/Rockledge Drive Interchange in Montgomery County.” Maryland Department of Transportation (MDOT), news release. November 4, 2003.
Page updated July 21, 2022.
