Marked north-south.

SHA I-270 strip map with interchange details, 1976.

I-270 is one of the oldest sections of freeway in Maryland, the first section being in place by 1953 (and before the Interstate system). The official map from that year shows it complete between route 109 and US 15 (now MD 85). It was made the new US 240, and I-70S when the Interstate system arrived in 1956. US 240 was co-signed until the early seventies, and in 1973 was changed to I-270, to eliminate suffixed Interstate numbers.

I-70S was to extend inside the Capital Beltway roughly along the Metro line, but this plan was killed along with almost all the other unbuilt DC area freeways.

The I-270 corridor in Montgomery County has developed rapidly over the last 30 years, and 270 itself has gone from a 4 lane dual to a 12-lane highway with local and thru carriageways and HOV lanes. It's the closest thing to Los Angeles there is in Maryland, and it's every bit that, California-sized backups and all.

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