It all started with a simple tweet, “Did you know milepost numbering begins in the south and west? So, MP 10 on I-15 is in the St. George area and I-80 Exit 115 is 115 miles from NV.” This has been such a handy thing to know, even away from our work environment, that we wanted to share it.
This information on its own is pretty simple however there are a few places around the state that complicate things. In several locations we have highways that run concurrently like U.S. 89 and U.S. 91 between Brigham City and Logan. U.S. 6 is another good example. It runs concurrently with other routes in several places. There’s U.S. 50 near the Nevada border, I-15 in southern Utah County, U.S. 191 between Helper and Price, and I-70 from Green River to Colorado.
The surprising part to us was that our followers wanted to know what we do on these concurrent highways, what mileposts are used. To be honest, it’s kind of tricky.
The way it works is when a route joins another route the first route’s mileposts are used. Wait, what? That IS tricky. Let’s try it with an example. U.S. 91 begins at I-15 southwest of Brigham City and continues to the Utah-Idaho state line near Franklin, Idaho. U.S. 89 joins this route at 1100 South in Brigham City and then leaves the route at 400 North in Logan. For this distance U.S. 91′s mileposts are used but, U.S. 89 mileposts aren’t forgotten, we don’t pick up in Logan where we left off in Brigham City. Instead the mileposts include the 25 miles where U.S. 89 ran concurrent with U.S. 91, so, the milepost on U.S. 89 in Brigham City where it joins U.S. 91 is 433 and the milepost on U.S. 89 in Logan where it leaves U.S. 91 is 458.
There you have it, more than you ever wanted to know about mileposts. If you’re ever curious, we have highway reference reports for every interstate, U.S. Highway, and state Route on our website.