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Interstate Types and History
Interstate Highway Types and the History of California's Interstates

Chargeable and Non-Chargeable Interstates

The Interstate System

First, to eliminate some confusion: 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 23 USC 109(b).
[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 mileage 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 chargeable to the mileage in the system, but were signed as part of the system.

Interstate Highway Funding

Over time, the approach to funding Interstate highways has changed. Originally, the distinction between chargeable and non-chargeable miles was an important one. Chargeable miles were those that counted against the total miles authorized by Congress in 23 USC 103(c)(2), which in 2026 stated: "(2) Maximum mileage.-The mileage of highways on the Interstate System shall not exceed 43,000 miles, exclusive of designations under paragraph (4)." Non-chargeable miles were those covered by 23 USC 103(c)(4): "(A) Additions.-If the Secretary determines that a highway on the National Highway System meets all standards of a highway on the Interstate System and that the highway is a logical addition or connection to the Interstate System, the Secretary may, upon the affirmative recommendation of the State or States in which the highway is located, designate the highway as a route on the Interstate System." Section (B) allowed designation of routes as "Future Interstate Routes". The key point is that 23 USC 103(c)(4) routes didn't count against the mileage allocated by Congress, and were not eligible for Interstate Completion Funds. These routes were signed as Interstate more to provide continuity for the traveling public, and to signal that the highway met Interstate standards. This is made clear in 23 USC 103(c)(4)(C): "(C) Financial responsibility.-Except as provided in this title, the designation of a highway under this paragraph shall create no additional Federal financial responsibility with respect to the highway."

The discussion below on chargeable and non-chargeable interstates was written by Caltrans in the 1990s. It was applicable then, but the distinctions discussed have disappeared. Still, it is important historically as it shows the history of interstate submissions by Caltrans. Since it was created in 1956, the Interstate system has seen limited growth in total mileage (chargeable + non-chargeable):
(Mileage Information Source: Ports to Plains Alliance: Highway Funding, retrieved 7/16/2026)

The original Interstate System began in the 1950s with a guaranteed 90 percent federal funding commitment, enabling rapid, coordinated national delivery. That system was largely completed by 1985 and formally concluded in 1992. Beginning in 1991, Congress acknowledged the need for continued Interstate expansion through the High Priority Corridors concept. This resulted in drastic changes in funding formulas.
(Source: Ports to Plains Alliance: Highway Funding, retrieved 7/16/2026)

According to the Caltrans Highway Design Manual, dated 8/8/2025, the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 was the first major transportation legislation since the Interstate System was enacted. ISTEA changed the established Federal-Aid system. During the 20 years prior to ISTEA there were four Federal-Aid systems: Interstate, Primary, Secondary, and Urban. Now under ISTEA, instead of four Federal-aid systems there are two, the National Highway System (NHS) and the Interstate System, which is a component of the National Highway System.
(Source: Caltrans Highway Design Manual, 8/8/2025)

In 2005, the Safe, Accountable, Flexible, Efficient Transportation Enhancement Act, Legacy for the Users, better known as SAFETEA-LU, was passed. SAFETEA-LU, invested in highway, transit and safety programs. While ISTEA created new federal-aid programs, SAFETEA-LU continued those programs such as the Surface Transportation Program, National Highway System, Congestion Mitigation and Air Quality Improvement Program and the Bridge Replacement and Rehabilitation Program.
(Source: Caltrans Highway Design Manual, 8/8/2025)

The Moving Ahead for Progress in the 21st Century Act (MAP-21) was signed into law in 2012 and streamlined the performance-based surface transportation program, establishing asset management as a key direction for  transportation funding. In 2015, the Fixing America’s Surface Transportation (FAST) Act was signed into law, providing the first federal law in over a decade to provide long-term funding for infrastructure planning and investment. The FAST Act maintained focus on safety, keeping intact the established structure of the various highway programs, continued efforts to streamline delivery, and for the first time, provided dedicated funding for freight projects.
(Source: Caltrans Highway Design Manual, 8/8/2025)

In November of 2021, the Infrastructure Investment and Jobs Act (IIJA) was signed into law.  The IIJA is the largest long-term infrastructure investment in our Nation’s history, providing federal investments in infrastructure including: roads, bridges, mass transit, water infrastructure, resilience, and broadband. In addition to our core federal aid programs, IIJA created new programs, including Promoting Resilient Operations for Transformative, Efficient, and Cost-Saving Transportation (PROTECT), Carbon Reduction Program (CRP), and the Bridge Formula Program (BFP), ensuring dedicated funding for specific scopes of work.
(Source: Caltrans Highway Design Manual, 8/8/2025)

A variety of other programs also continued to exist to provide flexibility in determining transportation solutions and promote a multi-modal system approach. Some of these programs include those that target funding for rail and transit projects while others provide funds for environmental enhancement such as habitat mitigation and wetland banking. Numerous other funding categories are also available for use during the five-year term of the latest act.
(Source: Caltrans Highway Design Manual, 8/8/2025)

With respect to Federal Aid: The focus is the National Highway System. To see a map of the NHS, visit the FHWA HEPGIS National Highway System Page. In 1995, the Secretary of Transportation proposed a National Highway System (NHS) consisting of approximately 160,000 miles across the United States. The NHS consists of all Interstate routes, a large percentage of urban and rural principal arterials, the defense Strategic Highway Network, strategic highway network connectors, and intermodal connectors. The Interstate Highway System is a part of the NHS, but retains its separate identity. As a condition of funding for Federal-aid highway projects, Federal law prohibits State departments of transportation from adding any point of access to or from the Interstate System without the approval of the Secretary of Transportation and all new or modified points of access must be approved by FHWA and developed in accordance with federal laws and regulations as specified in 23 U.S.C. 109 and 111, 23 C.F.R. 624 and 625.4, and 49 C.F.R. 1.48(b)(1). Revenue from the Federal gas and other motor-vehicle user taxes was credited to the Highway Trust Fund to pay the Federal share of Interstate and all other Federal-aid highway projects. In this way, the Act guaranteed construction of all segments on a "pay-as-you-go" basis, where the program is self-financing without contributing to the Federal budget deficit.
(Source: Caltrans Highway Design Manual, 8/8/2025)

In terms of Federal funding: The maximum share of project cost that may be funded with Federal-aid highway funds (the “Federal share”) varies based upon the Federal-aid program from which the project receives funding. In some cases, the Federal share is also adjusted based on related statutory provisions. The typical federal share under the sliding scale is 91.57 percent on Interstate projects and 88.53 percent on non-Interstate projects for federally eligible roads. 23 USC 120 dictates the Federal Share Payable. For Interstate projects, this is specified as "(1) In general.-Except as otherwise provided in this chapter, the Federal share payable on account of any project on the Interstate System (including a project to add high occupancy vehicle lanes and a project to add auxiliary lanes but excluding a project to add any other lanes) shall be 90 percent of the total cost thereof, plus a percentage of the remaining 10 percent of such cost in any State containing unappropriated and unreserved public lands and nontaxable Indian lands, individual and tribal, exceeding 5 percent of the total area of all lands therein, equal to the percentage that the area of such lands in such State is of its total area; except that such Federal share payable on any project in any State shall not exceed 95 percent of the total cost of such project." Certain specified types of projects, mostly targeting safety improvements, are eligible to receive a Federal share of 100 percent. A toll project under 23 USC 129 is eligible for a maximum Federal share of 80 percent  (regardless of whether the project would have qualified for a higher Federal share if advanced as a non-toll facility). 
(Source: Caltrans Highway Design Manual, 8/8/2025)

Congress has a detailed description of how funds are allocated between programs and states. The report is long and involved. The Gemini AI summary of the report is: "Congressional Research Service report R47922 details a shift in federal highway funding from traditional formula factors used between 1916 and 2012 to a mechanism based on historical percentage shares, beginning with MAP-21 and continuing through the Infrastructure Investment and Jobs Act (IIJA). The analysis shows that this reliance on historical baselines increasingly decouples funding from current state-level metrics such as population, lane miles, and vehicle miles traveled." My assessment of a quick read of the report is that the historical notions of percentage share funding based on shield type have become even more calculated, and the percentage allocated to each state from the overall highway trust funds is harder to determine.
(Source: CRS Report R47922, "The Highway Funding Formula: History and Current Status Under the Infrastructure Investment and Jobs Act", 2/15/2024)

As the original distinction between "chargeable" and "non-chargeable" Interstate mileage has gone away, and the old distinction of Federal-Aid-{Interstate, Primary, Urban, Secondary} (FAI, FAU, FAP, FAS) has gone away (deleted in 1991), it has been replaced with a system called Functional Classification. Functional Classification defines seven levels of highways:

  1. Interstate
  2. Other Freeway or Expressway
  3. Other Principal Arterial
  4. Minor Arterial
  5. Major Collector
  6. Minor Collector
  7. Local

The functional classification determines eligibility for Federal Funding programs. Caltrans has a page where it discusses functional classification (FC), and where it links to a map showing the functional classification of highways in the state system. There are detailed definitions for each level of classification, and those classifications also depend on whether the highway is urban or rural. The functional classifications are defined by the FHWA in the Highway Performance Monitoring System. It appears the current guidance for functional classification dates to 2023. As an example, this is the definition for "Other Freeway or Expressway":

Roadways in this functional classification category look very similar to Interstates. While there can be regional differences in the use of the terms ‘freeway’ and ‘expressway’, for the purpose of functional classification the roads in this classification have directional travel lanes are usually separated by some type of physical barrier, and their access and egress points are limited to on- and off-ramp locations or a very limited number of at-grade intersections. Like Interstates, these roadways are designed and constructed to maximize their mobility function, and abutting land uses are not directly served by them.

It appears that the functional classification for "Interstate" depends only upon designation by the Secretary of Transportation, and does not continue the distinction between "chargeable" and "non-chargeable".

The key point, for highway funding, is that roads with a functional classification of 1-3 are eligible to be part of the National Highway System; roads with a functional classification of 1-5 and 6 (urban only) are eligible for Federal Aid. There are a small number FC 4, 5, and 7 routes in the NHS.

Google AI summarizes the impact of the FC: Its primary purpose is to determine which roadways and transportation projects qualify for Federal-Aid Highway Program funds.Funding Eligibility Rules. Under federal law, funding eligibility heavily depends on the classification assigned to a road. Generally, eligibility breaks down as follows:

Chargeable 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 mileage 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 mileage to 43,000. Of these miles, California has been allocated 2,311 miles. This mileage is called "chargeable Interstate". All of this mileage 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 chargeable Interstate mileage:

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 CHARGEABLE MILEAGE (includes 7.0 "Howard-Cramer" miles) 2,311.5 2312.93

The following is a history of routes submitted for inclusion as chargeable miles in the Interstate system. Information and maps of the original Interstate proposals may be found at http://www.roadfan.com/intreg.html#yellowbk. 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.

Additional References:

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Non-Chargeable Interstate Routes

23 USC 139 23 USC 103(c)(4) of the US Code allows for the designation of certain highways as Interstate routes in addition to those that count against the authorized total mileage of the Interstate system. These highways are not eligible for regular Interstate Completion funds and are colloquially called "Non-chargeable Interstates". They are all functionally classified as Interstate. 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 Interstate Completion funds.

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-chargeable interstate mileage:

Route Description ( 23 US 139(b) 23 USC 103(c)(4)(B) mileage 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 23 US 139(b) 23 USC 103(c)(4)(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  23 US 139(b) 23 USC 103(c)(4)(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  23 US 139(b) 23 USC 103(c)(4)(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-chargeable interstate routes:

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© 1996-2024 Daniel P. Faigin.
Maintained by: Daniel P. Faigin <webmaster@cahighways.org>.