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I-370 is called the Sam Eig Highway, after a Russian immigrant who made his millions in suburban DC real estate, then donated land and money for synagogues, Methodist and Catholic churches, a Red Cross building and Holy Cross Hospital in Silver Spring. Mr. Eig died in 1982 at the age of 83. 
Controversial ICC would extend from 370's end
There are/were plans to build a new freeway, the so-called Intercounty Connector (ICC), from the end of I-370 eastward to US 1 at Laurel, Md. The 18-mile highway would range from 6 to 12 lanes. Some are positioning this as the first link of an outer D.C. beltway, which was first planned around 1960.
I-370 (proposed) Missouri
The mid-1990s vintage MO 370 freeway extends from I-270 across the Missouri River to I-70 at St. Peters. Some have said this would be a natural candidate for an interstate, and the choice of number supports that; but I haven't heard anything official on the topic.
One reason for MO 370 is to relieve traffic crossing the Missouri River on I-70 a few miles to the south: probably from "excruciating" to "merely unbearable". 
Anthony Boor wrote in late 2001:
"According to Daniel Bruno, who works for MODOT, the reason that MO 370 hasn't become I-370 yet is because MODOT has gotten into a big pillow fight with AASHTO. The former wants to keep the 370 number, but the latter wants to name it I-870. Their rationale is that the raison d'etre of the road, at least the ones MODOT gave, were to create a bypass to reach a circumferential loop. So AASHTO wants it to be an even numbered x70, and 870 is the only one left for MO to use."