How are Mile Markers Calculated

[Ric7308]

Okay, my brother-in-law asked me this question the other day and I don't have the answer. Thought I would ask those CalTrans guys.

How are the mileage markers that are on the little signs on the highways calculated?

Center of the road?
Outer edge?
Average of all the lanes?

Ric

[Jim Frame]

My observation is that they rezero the mileage each time the highway crosses a county line. I think there are standard cardinal directions for "up" -- that is, the mileage increases as the highway proceeds north or east (might be south or west, I don't recall).

I'm sure someone with certain knowledge of the subject will check in to set the record straight.

Merry Christmas, everybody!

[Ian Wilson]

The markers I've staked were based on the distance fromthe base station set up on brass on the side of the road.

We also laid out a set of "Known Mark" bars for calibration of the precise odometers for some of paint striping trucks. That was also based on distance along the shoulder.

I laid out mile bars on a highway for aerial speed calculations. Those were also based on distances along the shoulder.

Are we seeing a pattern here, yet, Ric?

Have a great and safe holiday!

I'm back in Temecula for 9 days with my family.

[Ric7308]

Ian,

Yeah, I believe I can see a trend there. Have a good time back down south and everyone have a nice and safe holiday.

Ric

[Jim Frame]

Adding grist to the mill, I found the following on page 10 of the California Bicycling Guide, published by Caltrans District 1 and available on the District 1 website (http://www.dot.ca.gov/dist1/d1transplan ... ide/10.pdf):

"Post mile markers are white metal plates found at various locations along State Highways. Post miles start at 0.0 at county lines or beginning of routes and increase in [northerly] and easterly directions."

I inserted the "northerly" because the original text left out a direction. It *could* be "southerly," but I doubt it.

Note that the link above is only for page 10 and is 233k in size. The whole guide -- 17.44mb -- is also available (http://www.dot.ca.gov/dist1/d1transplan ... bikeguide/).
.

[E_Page]

When I was with MI DOT, the mileage markers were placed as Jim says. On all CA roads that I've paid attention to this, it fits that same pattern.

[Ric7308]

Thanks All,

I knew about the directions, but just didn't realize how the mileage was actually calculated. Our tests coincided with what Ian stated. It seems to favor the shoulder or right outside edge of the pavement.

Ri

[Jim Frame]

I need to read more carefully -- I completely missed the focus of the original question. I never thought about what specific alignment the mileage followed. Ian's post makes sense now!

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[E_Page]

I didn't know that they were placed that precisely either. That bit of info may be useful someday.

[RAM]

Even mile on side of tghe highway and 1/2 mile on the other. when completing an encroachment work you must reference the post mile to the 0.1 mile

[Dave Lindell]

I always guessed the mileage markers were accurately and precisely placed using centerline stationing. The curves would average out. being on the inside shorter radius one time and the outside longer radius the next.

What I always wondered is whether they accounted for the slope. After all, stationing is measured horizontal. Then I figured that a 5% slope would have to be 800 miles long to add an extra mile to the horizontal distance.

[Ric7308]

Well Dave,

I have also been told that all Caltrans stationing is on Grid, not Ground.

Ric

[Ian Wilson]

The markers I've set are based on ground distances and accounted for the slope as well. The purposes for which I laid out markers was to calibrate odometers or to catch speeders. The actual ground disatnce, based on slope distances was critical.

[waterworks]

http://www.cahighways.org/numberng.html
Holy cow.