Here in North Carolina, a brand-new segment of I-40 opened recently. It completes a southern bypass of Greensboro. The new route is now officially I-40 and is 4 miles longer from east to west than old I-40 was.
With exit numbers corresponding to mile markers, and with mile markers starting at zero on the Tennessee border, the question becomes "what to do with mile markers from the western end of the new bypass all the way to Wilmington, NC, where I-40 ends?". One option would be to renumber every milepost and exit for some 220 miles or so. Another option would be to "fudge it" around Greensboro.
And fudge it we did. The mile markers along the new stretch of I-40 are "some 1.1 to 1.6 miles apart" according to the NCDOT, allowing for a count of 15 miles from the western side of Greensboro (which is what the old highway did) within the actual 19 miles traversed by the new route.
Now THAT ought to have the map scale readers, GPS software updaters, and all sorts of travelers just a bit baffled for some time to come, eh? So much for determining one's odometer error on a "long stretch of Interstate highway", too.