Sequential exit numbering & conversion to milepost exit numbering

[J N Winkler]

At the time they were originally introduced, California "postmiles" were actually station markers rather than mileposts per se.  I suspect, but cannot definitely prove, that a county-based system was adopted for computational convenience.  For Mexico-to-Oregon routes like US 101, 99, etc. and other very long multi-county routes, the maximum values that have to be dealt with are much lower in a county-based system than in a statewide system.

To be fair to Caltrans, I don't think it was ever the intention that the postmiles be used for motorist navigation.  Caltrans considered the milepointing issue in a major retrospective of guide signing issues in the early 1960's and it is clear that any system introduced for motorist navigation would be distinct from the postmile system (Caltrans considered "paddle" mileposts at this time).  My recollection is also that the final report on the exit numbering study in 1972 recommended not just that exit numbers be installed, but also that consideration be given to provision of mileposts in rural areas, milepointed on a statewide rather than county basis to maintain relatability with the exit numbers.  But the Caltrans brass spiked that study, probably for cost and presentational reasons.  (The copy of it I found in the Caltrans library was stapled to a green-ink letter from a member of the public who was angry that exit numbers, mileposts, etc. were even being considered as opposed to, say, spending the money on new schools.)

Clued-in motorists depend on the postmiles by default because statewide mileposting is just not a service Caltrans provides at present, except (according to Wikipedia) on a pilot basis on certain freeways.  But, as Jake and I have both found, the postmiles are unhelpful where they are not outright misleading.

[agentsteel53]

the only value I get out of CA postmile paddles is that they have the letter R if it is a post-1963 realignment, which means that if I am clever, I can find the old alignment nearby.  Oh and sometimes they have an older route number - there's a 395 postmile in Escondido, some 7s left on the 710 freeway, and some 11s on the 110.

[myosh_tino]

IMO, JN Winkler is correct in that the white postmiles that are found on California's highways were not meant to be used by the motoring public.  Instead, they are reference markers that are used by CalTrans and local governments for maintenance and route logging purposes.  I never used postmiles to calculate distances because they are hard to read and are not posted at regular intervals.

Like I said in a previous post, the only highway that has standard green mileposts is Hwy 58 between Bakersfield and Barstow.  They first appeared on the Mojave Bypass freeway and have since been extended over the Tehachapi mountains.  I'm driving to Las Vegas next week so it'll be interesting to see if the use of mileposts has expanded.

[hbelkins]

It's not unusual on non-interstates.  Illinois uses a county based mileposting system for state and US routes.  It's a green cricle with the following inside:
{route number - black on white}
{county - white on green bar}
{mileage - black on white}

Thus:

83
DUPAGE
8

I can't seem to find a photo of one online.

I have a few of them on millenniumhwy.net

[Brandon]

I have a few of them on millenniumhwy.net

Thanks, HB, just found this one, third photo down on the page. 

http://www.millenniumhwy.net/signs%26sights/il/gallatin/index.html

[Duke87]

The [mu] and [m] variables are the same thing, is one of them supposed to be median? 

Whoops, documentation error. Yeah, µ is the mean, m is the median.

[Alex]

I have another example of the mileposts used on non-Interstate Illinois highways:

[joseph1723]

Ontario used to post sequential exit numbers until May 1, 1982 when they were changed over to our current system which is posting them by the nearest km post according to thekingshighway.ca

[vdeane]

I thought they used sequential, switched to mile-based, and then switched to km-based shortly thereafter?

[Brandon]

I thought they used sequential, switched to mile-based, and then switched to km-based shortly thereafter?

IIRC, that's what Quebec did.

[vdeane]

And to think I remeber reading somewhere that that's how 401's numbers went.  Can't find it now, though.