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I-197 (cancelled) Maryland
A proposed numbering in the 1970s and 1980s for a portion of US 50/301 from I-97 toward Annapolis. I-97 itself was proposed to continue west on US 50/301 back to I-95/495 near Washington D.C., forming two sides of a triangle between Baltimore, Annapolis, and the nation's capital.
In 1978 Interstate 197 was allotted 0.8 miles . In a circa 1980 plan, I-197 was listed at about 4 miles, terminating at MD 70.  In 1982 this was still the case, and I-197 was approved.  But in 1983 I-197 was removed from the plan.
Dropping I-197 makes sense, as it was just another numbering for a road that already had two (US 50 and US 301). In fact, US 50/301 is now officially I-595 between I-495 and MD 70, but is not signed as such for the same reasons.
Earlier I had written that I-197 was proposed for the MD 665 freeway south of Annapolis, but that apparently was just a rumor, gleaned from an MTR post in 1997.
See also: Non-Indiana Highways (Stephen Summers; I-197 and I-297 scans and lots of other neat stuff)
I-297 (cancelled) Maryland
A proposed freeway upgrade of MD 3 between I-97 at Millersville and US 50/301 at Bowie. This was first proposed in the 1970s, and canceled around 1990. It was part of the package with I-68/US 50 and I-97 that was approved in the mid-1980's. 
In November 2002, the State Highway Administration revealed a half-dozen alternatives for improving the MD 3 corridor. None of them include a full freeway, but some include grade separations and and interchange at MD 450. 
Until 1983, I-97 was also proposed to follow US 50/301 from Annapolis back to I-495 at Washington, D.C. forming two sides of a triangle; then I-297 would have met I-97 twice. In 1983, the US 50/301 route proposal was changed to Interstate 68. Now, it is unsigned I-595.
See also: Non-Indiana Highways (Stephen Summers; I-297 and I-197 scans and oodles of other groovy stuff)