Bob Goudreau: I-numbers galore

December 19, 2013 

The writer of the Dec. 17 letter “Wrong number” criticized the selection of Interstate 495 as the new designation for the U.S. 64 link between Raleigh and Rocky Mount. He correctly pointed out that a three-digit interstate with an odd first digit represents a spur connected to its parent interstate at only one end. But he was off-base in asserting that even-numbered prefix digits are reserved for loops that connect to their parent at both ends.

Actually, such a number indicates that the road terminates at an interstate highway (but not necessarily the parent interstate) at both ends. Since the new I-495 will connect to I-95 at one end and to I-440 at the other, it obeys the rule. Other examples of this practice include I-270 in Maryland (southern terminus at the I-495 Capital Beltway) and I-464 in Virginia (northern terminus at I-264).

As a side benefit of this change, I-540 will no longer technically be a spur; it will now run from I-40 in Durham County to I-495 in eastern Raleigh. The DOT could, if it chose, address the writer’s other complaint by renumbering I-540 to I-640. This would not be possible without I-495, as the Outer Loop’s future interchange with I-40 in Johnston County will be on a segment of the non-interstate N.C. 540 toll road.

Bob Goudreau

Cary

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