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.
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.