Interstate 370 Maryland

Interstate 370 Maryland


Interstate 370 connects I-270 with the Intercounty Connector (ICC) toll road east in Montgomery County, Maryland. Located between the cities of Gaithersburg and Rockville, I-370 carries commuter traffic west to Sam Eig Highway and east to Shady Grove Metro Station. Prior to construction of the ICC, I-370 concluded at the exchange with Shady Grove Road and the access road to Shady Grove Station. Inventoried as MD 200A, this connection remains but is no longer included in the Interstate System.

Designated Maryland State Route 200, the Intercounty Connector extends east from a trumpet interchange with Interstate 370 and MD 200A. The 17.5 mile long toll road winds through suburban areas north of the Capital Beltway to Interstate 95 and U.S. 1 near Laurel. Operated by the Maryland Transportation Authority (MDTA), the expressway uses all electronic toll (AET) collection.


The American Association of State Highway and Transportation Officials (AASHTO) approved Interstate 370 between I-270 and the vicinity of Shady Grove on November 15, 1975. The freeway, part of a once proposed outer beltway, opened to traffic on December 17, 1988.1 Completion of the Intercounty Connector Project shortened I-370 from 3.13 to 2.54 miles. The truncation to MD 200 was conditionally approved by AASHTO on November 16, 2012.

Route Information

  • East End – Washington Grove, MD

  • West End – Gaithersburg, MD

  • Mileage – 2.54

  • Cities – Gaithersburg, Rockville

  • JunctionsI-270

Source: December 31, 2021 Interstate Route Log and Finders List

I-370 Annual Average Daily Traffic (AADT)

Location Vehicles per day
MD 119 to I-370 35,921
I-270 to MD 355 98,390
MD 355 to MD 200 88,670
MD 200A 22,531

Intercounty Connector

A Draft Environmental Impact Statement (DEIS) was released for the Intercounty Connector project in December 2004, with a toll feasibility analysis completed afterwards.2 The preferred corridor was the southern alignment.3 A Record of Decision was released by the Federal Highway Administration (FHWA) on May 30, 2006.4

Construction on the ICC began in November 2007 after nearly 50 years of debate on whether to build it.5 The ICC is not planned to be designated as a part of Interstate 370.6 Plans called for the six lane, $2.4 billion tollway to fully open in 2012. The phases for construction were:7

  1. Contract A – connect Interstate 370 and MD 97 / Georgia Avenue (7.2 miles, construction from 11/13/07 to Fall 2010; $478.7 million cost)
  2. Contract B – connect MD 97 / Georgia Avenue with U.S. 29 (7.0 miles, construction from Mid 2008 to Late 2011; up to $460 million cost)
  3. Contract C – connect U.S. 29 with I-95 (3.7 miles, construction from 1/14/08 to Late 2011, $513.9 million)
  4. Contract D – construct collector distributor roadway system between ICC and I-95 (three miles at a cost up to $75 million) – construction slated from 2010 to 2011 or 2012

The ICC fully opened between I-370 and I-95 on November 22, 2011. The 1.5 mile extension from I-95 east to U.S. 1 at Laurel opened to traffic on November 10, 2014.

East End Maryland Route 200 Inner County Connector Maryland Route 200A – Washington Grove, Maryland

I-370 East at MD 200 MD 200A

I-370 east at MD 200 - Washington Grove, MD

A trumpet interchange (Exit 3B) joins the east end of Interstate 370 with unsigned MD 200A south to Shady Grove Road and Shady Grove Metro Station and the ICC east to Prince George’s County. 06/20/12

I-370 east at MD 200 - Derwood, MD

An end shield for I-370 previously stood within the six-ramp parclo interchange connecting MD 200A with Shady Grove Road. Photo by Jeff Royston (06/10/06).

MD 200 West at I-370 MD 200A

MD 200 west at I-370 - Washington Grove, MD

Westbound MD 200 (ICC) transitions into Interstate 370 beyond the departure of Exit 3 for MD 200A south to Shady Grove Road. The lone indication of I-370 along the ICC west is this assembly. 06/20/12

MD 200A North at I-370 MD 200

MD 200A north at I-370/MD 200 - Washington Grove, MD

Interstate 370 extends west from MD 200 (ICC) and the exchange with MD 200A. I-370 formerly curved westward here ahead of MD 355 in Gaithersburg. 06/20/12

West End I-270 / Sam Eig Highway – Gaithersburg, Maryland

I-370 West at I-270

I-370 west at I-270 - Gaithersburg, MD

A left exit joins Interstate 370 west with I-270 south to Washington. I-370 formally ends 0.6 miles ahead by Washingtonian Boulevard. The freeway extends 0.2 miles further to a signalized intersection with Fields Road. 06/20/12

I-370 East at I-270

I-370 east at I-270 - Gaithersburg, MD

The zero milepost for I-370 per the MDOT Highway Location Reference (HLR) is located at the merge point from the I-270 north to Sam Eig Highway westbound ramp. This point falls within the diamond interchange at Washingtonian Boulevard. Photo by Jeff Royston (06/10/06).

I-370 east at I-270 - Gaithersburg, MD

An auxiliary lane opens eastbound from Washingtonian Boulevard to I-270 south. Shady Grove Metro Station was greened out for Interstate 370. 06/20/12

I-370 east at I-270 - Gaithersburg, MD

The connection from I-370 east to I-270 north to Frederick is the lone loop ramp within the turbine interchange between the two freeways. 06/20/12

I-370 east at I-270 - Gaithersburg, MD

The lone eastbound confirming marker was posted at the Oakmont Avenue underpass. The assembly was removed during expansion of I-370 to six lanes in 2008-09. Photo by Jeff Royston (06/10/06).

I-270 North at I-370

I-270 north at I-370 - Gaithersburg, MD

Exit 9A departs from the Local Lanes of Interstate 270 north for both I-370 east to the Inner County Connector (MD 200) and Sam Eig Highway west to MD 119 (Great Seneca Highway). 08/04/13


  1. Interstate 370. Wikipedia.
  2. “Maryland’s ICC may not need any tax money – for Maryland Taxpayers Association.quot; Toll Road News, March 24, 2005.
  3. Southern Route for Connector EndorsedWashington Post (DC), February 4, 2005.
  4. Posts from misc.transport.road newsgroup: “Maryland ICC Record of Decision and Groundbreaking” by Scott M. Kozel, 05/31/06 and “Re: Maryland ICC Record of Decision and Groundbreaking” by Scott M. Kozel, 05/31/06.
  5. With Obstacles Overcome, Highway Work Begins: Quietly, Barriers and Dirt Emerge at Scattered Sites.Washington Post (DC), November 29, 2007.
  6. Wolf, Joe. “Another Interstate Guide update.quot; Personal Email, 12/17/07.
  7. ICC Project Schedule, accessed on January 2008.

Page updated December 11, 2020.