Questions often arise on the control cities for California Interstates. Information on Control Cities in general can be found here. Specifically, according to the MUTCD:
The direction of a freeway and the major destinations or control cities (see Section 2D.34) along it shall be clearly identified through the use of appropriate destination legends. Successive freeway guide signs shall provide continuity in destination names and consistency with available map information. At any decision point, a given destination shall be indicated by way of only one route.
Control city legends are required to be used at interchanges, separation points of overlapping freeway routes, on directional signs on intersecting routes, on Pull-Through signs, and on the bottom line of post-interchange distance signs.
The control cities defined for California Interstates are as follows:
|I-5 NB||San Diego, Santa Ana, Los Angeles, San Francisco, Sacramento, Redding, Mt. Shasta City, Weed, Yreka, Ashland (OR)|
|I-5 SB||Ashland (OR), Yreka, Weed, Mt. Shasta City, Redding, Sacramento, San Francisco, Los Angeles, Santa Ana, San Diego|
|I-8||San Diego, El Centro, Yuma (AZ)|
|I-10||Santa Monica, Los Angeles, San Bernardino, Riverside, Indio, Blythe, Phoenix (AZ)|
|I-15||San Diego, Riverside, San Bernardino, Los Angeles, Barstow, Las Vegas (NV)|
|I-40||Barstow, Needles, Kingman (AZ)|
|I-80||San Francisco, Sacramento, Reno (NV)|
Other routes do not have control cities—they are forward directions. The difference is that continuous signing is (nationally) guaranteed for a control city. It appears on every pull-through sign on the Interstate leading to it until it is reached, then the next control city appears on every pull-through until that is reached, and so on. This doesn't work for things like loop routes (3-digits) or spurs (which might be within a city); and AASHTO doesn't have jurisdiction over the state routes.
But, just to confuse things, the term "control city" is also used at the state level, in a more broader sense, to refer to any one on a list of forward destinations that are to be signed on the state highway system (not just Interstates or freeways). Examples of documents referring to designated control cities are Caltrans' own 'MUTCD.' Supplement (which, however, only directs the Districts to come up with control city lists--no set of control cities is actually given in the Supplement). Often, the forward destinations are the ultimate destinations, or (such as with I-405) the names of cities reachable with the next Interstate connection (Sacramento, Santa Monica, Long Beach, San Diego).
Introduction to Interstate Highway Types History of California's Interstates
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