The mileage marker mystery mentioned in the In One Ear column last week is explained! The “thank yous” go to Paul Christiansen, project manager, Oregon Department of Transportation, Astoria construction, who kindly provided the answer:

“The phenomenon of apparently erroneous mileposts is common for highways across the country, and there is a relatively simple explanation.

“When the highway was originally built, mileposts were placed in accurate locations. With time, as the highway alignment is changed because of construction projects or natural phenomena such as slides, the original highway length changes.

“Rather than redo all of the affected mileposts when this happens, engineers insert an ‘equation station’ in the highway alignment. An equation station is a point in the highway where the mileage reference point changes; it might be written like ‘behind MP 79.1, ahead MP 80.5,’ which would illustrate a sudden 0.6 mile ‘jump’ in mileage.

“Imagine taking a tape measure and forming a loop by putting the 8 inch mark next to the 6 inch mark; the overall length is shortened, but distance between each of the inch marks on the tape are still one inch.

“An example of this on U.S. Highway 30 is the realignment that resulted in the remnant that became Old Highway 30. The equation station can go the other direction as well; between Wheeler and Rockaway the highway alignment was lengthened to accommodate the Brighton Slide. In that area, ODOT has added ‘Z’ to the mileage markers. Look for the Z posts next time you’re on this section of U.S. Highway 101.”

The Ear humbly apologizes for thinking those hard-working ODOT guys had an issue with counting while setting up those mile-markers!