Also known as the Sam Eig
Highway. A very short highway
(2.67 miles) Parallel
ing Shady Grove Rd. in Montgomery County, Maryland
connecting Interstate 270
with the Shady Grove Metro
If the Intercounty Connector is ever built, Interstate 370 will serve as the first few miles. According to the Interstate Numbering System, 370 would imply that it's a "bypass between highways", which is pretty accurate for the Intercounty Connector which is to connect Interstate 270 with Interstate 95 but not at all true for it's lame state today.
It's a federal road, which means that when it snows, the road is cleared very quickly. It's entirely concrete, which makes for a very loud driving experience.
In addition, there is a proposed I-370 in Missouri which will connect Interstate 270 with Interstate 70 at St. Peters and will include a crossing of the Missouri River.
I got some of this info (especially the stuff about Missouri) from http://www.kurumi.com/roads/3di/i370.html.