Understanding mile post markers on Nevada highways

OK, a storm came through last night — Time to check nvroads.com (511 Home) and see about road conditions. It is a very slow website this morning as might be expected when a couple of inches of new snow greets the morning.On US 395 north of Reno, the highway is purple and a click provides a popup that says “There is a conditions related event (Chains or Snow Tires Required) on US-395 from mile post 26.0 in Washoe County to mile post 42.1 in Washoe County in Nevada“. This is confusing. The freeway exit numbers on that stretch of US 395 are in the 70’s so what is this mile post 26 to 42 label?

To figure that out, see the NV DOT page on Milepost Signs.

On interstates, two types of mileposts exist. Green post mile markers list the mileage from the state line while white and black standard mileposts list the mileage from the county line. U.S., state and other routes strictly list the mileage from the county line.

For the purpose of milepost signs, roadway mileage numbers start from the south or west end of where a road first enters a state or county. The mileage number continues to build as the road travels north or east.

Safety Recommendation

It is recommended that motorists be aware of milepost signs, particularly while driving in rural areas. Knowing your milepost location will allow for quicker response if needing to call for emergency assistance.

It looks like the road conditions report is for the “black standard mileposts” and not the green interstate ones. The standard mileposts have a two letter county identifier below the highway number while the green ones don’t. The road distance from the south or west is on the bottom of the sign and rotated 90 degrees on the standard signs. New road construction projects are installing larger milepost signs a bit off the road at 5 feet above the road surface. These are intended to be easier to see and less likely to get run over or otherwise damaged.

Milepost markers are the DOT’s coordinate system. That’s fine for them but many of us aren’t keeping an eagle out for each passing milepost sign or aren’t using that coordinate system often enough to know where we are by that system. Instead we call for help using routes and landmarks or we turn it over to computers. The computers are what NVDOT uses to show road conditions on the map at nvroads.com. If you need a list of the source data rather than a map, see the incidents list page.

Google is a step up the ladder in that every driver with an Android phone that allows position reporting provides Google with current traffic data that it can show on its map. Google bought the Waze app to help facilitate this effort. This is a social network where drivers can share information about roads and routes in real time. That is how, for instance, Google maps can show two crashes and one other incident on US 395 north of Reno this morning along with the red colored highway to indicate slow moving traffic. The position reporting is, of course, by GPS coordinates but it is all behind the curtain. What we see is a map with coded information for our travel needs. Note that this is a two way street. You don’t get this information unless you let your device report its position and speed. 

It should also be noted that cell phones have been required to report position to dispatchers on 911 calls for quite a while. They use GPS for this if available or cell signal strength data otherwise. (this is similar to how home computers are using wifi signals to assist localizing I’net searches now). Again, this is a ‘behind the computer curtain’ kind of thing. You could query your GPS for coordinates and read them over the phone, too, but the chance for error is rather high for that sort of thing. An alternative would be to have a macro read the phone GPS data and send it via SMS (gotta’ love all those TLA’s – three letter acronyms!).

Interstate mile markers are most visible on maps as exit numbers. Otherwise, mile markers are scarce on maps. It might be a good project to write a program to use Navigation software to trace a route back to its start or its southern or western intersection with a state or county line, calculate the route from there to a selected position, and then use the distance of that route to report the mile marker. That would be a non trivial exercise. That’s why the color coding at nvroads.com is very useful as the DOT has done the converting between there mile markers and something that is a bit easier for the regular driver to understand.

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