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California Highways

Interstate Highway Types and the History of California's Interstates

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Interstate Highway Types

As defined in the state highway code, there is no distinction between "Interstates", "US Highways", and state highways -- they are all state highways.

Federal law is different. Federal Law (specifically 23 USC 103, which was significantly reworked by Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991) defines two highway systems: the National Highway System (NHS) and the Interstate System, which is a component of the National Highway System. Note that this is a change from the original method of Interstate funding, where there were four Federal-Aid systems: Interstate, Primary, Secondary, and Urban.

The Interstate system (formally "The Dwight D. Eisenhower System of Interstate and Defense Highways") serves the 48 contiguous states, Alaska, Hawaii, Puerto Rico, and the District of Columbia. It carries more than 21 percent of the nation's traffic on only 1% of the nation's total road and street milage. A good history of the interstate system can be found at Stephen Summers has created a nice page on the history of the interestate system at There are specific design requirements for Interstate highways, and all highways classified as Interstate (with the exception of those in Alaska and Puerto Rico) must meet those standards. The goals of the highways on the Interstate system are to:

  1. To connect by routes, as direct as practicable, the principal metropolitan areas, cities, and industrial centers.

  2. To serve the national defense.

  3. To the maximum extent practicable, to connect at suitable border points with routes of continental importance in Canada and Mexico.

The Interstate system has a maximum number of miles defined in law: it cannot exceed 43,000 miles (currently, it is at 42,795 miles). This milage does not include milage signed as interstate under 23 USC 103(4). Such milage is colloquially called "non-chargeable" milage.

Under ISTEA, the Interstate Program includes completion funding for Interstate Construction, Interstate Substitute highway projects, and an Interstate Maintenance program to rehabilitate, restore, and resurface the Interstate system. Reconstruction is also eligible for funding if it does not add capacity, except for high occupancy vehicle (HOV) or auxiliary lanes. Federal Aid comes in multiple forms. The Surface Transportation Program can be used on Interstate, National Highway System, and all roads functionally classified by FHWA as other than local or rural minor collectors. The Congestion Mitigation and Air Quality Improvement Program is directed towards transportation projects which will contribute to Clean Air Act requirements in non-attainment areas for ozone and carbon monoxide. The Bridge Replacement and Rehabilitation Program is continued.

According to the FHWA, to mark the Interstate routes, the American Association of State Highway Officials (AASHO) asked its member states to submit suggestions. The States submitted dozens of ideas in several forms, ranging from a 55mm color transparency to a 4-foot square aluminum blank. The signs were tested, an a final version, a combination of submissions from Missouri and Texas, was selected. On September 19, 1967, the U.S. Patent and Trademark Office issued Trademark Registration 835,635 for the shield.

Control Cities

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 'M.U.T.C.D.' 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).

History of California's Interstates

First, to eliminate some confusion, thanks to a posting by Paul Wolf: All highways in the US, except on federally-owned land (such as within national parks) are state or locally maintained, although many are eligible for federal aid in construction. The Interstate system created in 1956 has a specific set of design criteria, and specific funding ratios. The design criteria and funding ratios are different from that of the 1926 Federal system. The standards include a minimum of four 12-foot wide travel lanes, a minimum shoulder width of 10 feet, full control of access, and design speeds of 50 to 70 miles per hour (depending on the type of terrain). Initially, the design had to be adequate to meet the traffic volumes expected in 1975. Later, the requirement was changed to a more general 20-year design period rather than for a specific year to allow for evolution of the System. The design standards have been codified in Section 109(b), 23 U.S.C.
[Information on the Design Standards from the FHWA Interstate Log]

The Federal government, working with the states, established the system (i.e. designated the general corridors, but not the exact locations) and allocated the milage to the states. The states designed and built the roads, with the Federal government reviewing and approving the plans. States could, and did, decide not to build portions of the system. There are also routes built to the standards of the system, usually with some percentage of federal money, that were not chargable to the milage in the system, but were signed as part of the system.

Chargable Interstate Routes

The Interstate System was created by the 1944 Federal-Aid Highway act, which authorized 40,000 miles nationally. California was initially allocated 1,938 miles. Later allocations in 1955 brought the total milage to 2,135 miles. The 1956 Federal-Aid Highway Act authorized an additional 1,000 miles nationally; California received none of this. The 1968 Highway Act added another 1,500 miles, expanding the system to 42,500 miles. An amendment sponsored by U.S. Representatives James Howard and William Cramer authorized an additional 200 miles for modification or revision of the basic System. The mileage authorized under the Howard-Cramer Amendment was increased eventually to 500 miles under the Federal-Aid Highway Act of 1973. The Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 brought the total authorized milage to 43,000. Of these miles, California has been allocated 2,311 miles. This milage is called "chargeable Interstate". All of this milage is/was eligible for construction with regular Interstate funds.

The Surface Transportation Assistance Act of 1978 provided full Interstate Construction funding for all routes designated under previous System adjustments. Another provision of this Act prohibited the use of Interstate Construction (IC) funds for the construction of any new miles designated after passage of the Act. A total of 42,795 miles had been designated for development with IC funds before this measure was enacted.

The following summarizes California's chargable Interstate milage:

Route Description Miles Miles Per FHWA Log
I-5 International Boundary near Tijuana, Mexico to the Oregon state line near Ashland, Oregon 797.0 796.53
I-8 I-5 in San Diego to the Arizona state line near Yuma, Arizona 170.0 169.92
I-10 Santa Monica to I-5 in Los Angeles and from I-5 in Los Angeles to the Arizona state line near Blythe 240.9 242.54
I-15 I-8 in San Diego to the Nevada state line near Las Vegas, Nevada 287.3 287.26
I-40 I-15 in Barstow to the Arizona state line near Kingman, Arizona 154.6 154.61
I-80 First Street in San Francisco to the Nevada state line near Reno, Nevada 202.2 199.24
I-105 Route 1 (Sepulveda Blvd) at the Los Angeles International Airport to I-605
*: I-105 includes 7.0 "Howard-Cramer" miles.
*17.3 17.32
I-110 Route 47 in San Pedro to I-10 in Los Angeles 20.5 20.43
I-205 I-580 W of Tracy to I-5 E of Tracy 13.0 12.97
I-210 I-5 near Tunnel Station to I-10 near Pomona 48.6 48.72
I-280 I-680 in San Jose to Sixth Street in San Francisco 57.1 57.22
I-305 I-80 W of Sacramento to Route 99 in Sacramento. (Signed as US 50) 5.3 8.44
I-380 I-280 S of San Francisco to the San Francisco International Airport 3.3 3.30
I-405 I-5 near El Toro to I-5 near Tunnel Station 72.4 72.15
I-505 I-80 near Vacaville to I-5 near Dunnigan 33.0 32.98
I-580 Vicinity of Castro Street in Richmond to I-80 in Albany, and from I-80 in Oakland to I-5 near Tracy 68.4 67.83
I-605 I-405 near Seal Beach to I-210 near Azusa 27.4 27.40
I-680 I-280 in San Jose to I-780 in Benicia 58.0 58.02
I-780 I-80 in Vallejo to I-680 in Benicia 6.5 6.50
I-805 I-5 S of San Diego to I-5 N of San Diego 28.0 28.02
I-980 I-880 in Oakland to S of the San Pablo undercrossing 0.8 1.03
TOTAL CHARGABLE MILAGE (includes 7.0 "Howard-Cramer" miles) 2,311.5 2312.93

The following is a history of routes submitted for inclusion as chargable miles in the Interstate system. Information and maps of the original Interstate proposals may be found at Note that these dates are based on those shown in the Caltrans history of Interstate submissions. They may correspond to initial submission dates, or dates the basic route was approved, but not necessarily the number.

Non-Chargable Interstate Routes

Section 139, Title 23 of the US Code allows for the designation of certain highways as Interstate routes in addition to that which is "chargeable". These highways are not eligible for regular Interstate Completion funds and are called "Non-chargeable Interstates". They are all Federal-aid Primary highways that meet the criteria for Interstate routes. They are signed as interstates to provide continuity and connectivity for motorists and truckers. There are two types:

Note that the section numbers have changed. According to the FHWA log:

The FHWA may, at the request of a State or States, designate sections of the National Highway System (NHS) as Interstate Highway under Section 103(c)(4)(A), Title 23, United States Code (23 U.S.C.). The proposed section must:

Although Section 103(c)(4)(A) segments look like any other Interstate highway, they are not eligible for development with IC funds. In all, the FHWA has approved 2,145.29 miles of highways in the contiguous 48 States, District of Columbia, and Hawaii as Section 103(c)(4)(A) additions to the Interstate System (including additions under former Section 139(a)).

Also added to the Interstate System under Section 103(c)(4)(A) are highways in Alaska and Puerto Rico for a total of 1,331.99 miles (including additions under former Section 139(c)). Alaska and Puerto Rico are exempt from the design standards of Section 109(b). Section 103(c)(1)(B)(ii), 23 U.S.C., states: "Highways on the Interstate System in Alaska and Puerto Rico shall be designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway."

The FHWA may also, at the request of a State or States, add highways to the Interstate System that are designated as National Highway System (NHS) high priority corridors and future parts of the Interstate System in Section 1105 of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). The proposed section must:

The following is a summary of California's non-chargable interstate milage:

Route Description (139(b) milage is still non-interstate and not counted in the FHWA log) Miles Miles Per FHWA Log
I-215 Temecula to Devore (6.2 mi is still 139(b)) 60.20 54.50
I-238 Between I-580 and Route 17 in San Leandro. 2.0 2.23
I-680 Between Benicia and Cordelia. 12.0 12.50
I-580 Castro Street in Richmond to US 101 in San Rafael 7.0 7.30
I-710 Ocean Blvd in Long Beach to I-10 (1.6 mi is still 139(b)) 21.6 19.66
I-880 San Jose to I-80 45.0 47.22
I-905 Route 117/125 from I-5 to the Mexico border (all 139(b)) 8.80 0.0
I-980 The constructed freeway portion of I-980 between I-580 and 1 mi S, 1.0 1.00
TOTAL 158.0 144.41

The following is a chronology of California's non-chargable interstate routes:

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