What Is the Difference Between U.S. and Interstate Highways?

[Jim B.]

They both go from state to state. They are both apparently owned by the U.S. government. Yet they are both two different types of roads. What exactly is the difference between the U.S. and Interstate road systems?

I would just add to my question above that I have a vague recollection of reading in high school that the Interstate system was designed by the Eisenhower administration in the 1950's to replace the ineffective U.S. system. The Interstate certainly is the preferred way now, especially when traveling from state to state. But why didn't they just turn the U.S system into the Interstate system then?

Does anyone know the answer to these questions?

[Earl Snake-Hips Tucker]

The biggest difference is that the Interstate Highways are always limited access. I don't think there were many limited access highways before the Interstate Highway System was created.

[RealityChuck]

US highways are older and were originally two-lane. The Interstate highways were created under the interstate system in the 1950s (the system is officially named after Eisenhower).

It was easier to build new multilane highways than to widen existing US routes, many of which had homes and businesses alongside and not enough room for four lanes. Better to build the roads on land that wasn't built up.

[brianmelendez]

The National Highway System includes the Dwight D. Eisenhower National System of Interstate & Defense Highways, known as the "Interstate System," and all other federal-aid highway systems:

Sec. 470.107 Federal-aid highway systems.

(a) Interstate System.

(1) The Dwight D. Eisenhower National System of Interstate and Defense Highways (Interstate System) shall consist of routes of highest importance to the Nation, built to the uniform geometric and construction standards of 23 U.S.C. 109(h), which connect, as directly as practicable, the principal metropolitan areas, cities, and industrial centers, including important routes into, through, and around urban areas, serve the national defense and, to the greatest extent possible, connect at suitable border points with routes of continental importance in Canada and Mexico.

(2) The portion of the Interstate System designated under 23 U.S.C. 103 (e)(1), (e)(2), and (e)(3) shall not exceed 69,230 kilometers (43,000 miles). Additional Interstate System segments are permitted under the provisions of 23 U.S.C. 139 (a) and (c) and section 1105(e)(5)(A) of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), Pub. L. 102-240, 105 Stat. 1914, as amended.

(b) National Highway System.

(1) The National Highway System shall consist of interconnected urban and rural principal arterials and highways (including toll facilities) which serve major population centers, international border crossings, ports, airports, public transportation facilities, other intermodal transportation facilities and other major travel destinations; meet national defense requirements; and serve interstate and interregional travel. All routes on the Interstate System are a part of the National Highway System.

(2) The National Highway System shall not exceed 286,983 kilometers (178,250 miles).

(3) The National Highway System shall include the Strategic Highway Corridor Network (STRAHNET) and its highway connectors to major military installations, as designated by the Administrator in consultation with appropriate Federal agencies and the States. The STRAHNET includes highways which are important to the United States strategic defense policy and which provide defense access, continuity, and emergency capabilities for the movement of personnel, materials, and equipment in both peace time and war time.

(4) The National Highway System shall include all high priority corridors identified in section 1105(c) of the ISTEA.

For more information about the National Highway System's components, see the relevant statutory provisions on federal-aid systems, 3 U.S.C. § 103; the Federal-Aid Policy Guide, 23 C.F.R. pt. 470A; and the Department of Transportation, Federal Highway Administration, What is the National Highway System?.

The Interstate System is named after President Eisenhower because his administration advocated and presided over its institution in the 1950s. But his interest in a strong nationwide transportation network stemmed from his being assigned, as a young Army officer, to devise a cross-country route for the rapid transcontinental deployment of military transport and other materiel.

[tomndebb]

One really big difference is that U.S. highways are simply state highways with no Federal input on planning.

In 1922 (1923?) a number of states, realizing that the automobile was changing the way people perceived travel and cartage) got together and agreed to establish a network of highways in which a single identifying number would cross multiple states. There was no direct Federal involvement in the organization and implementation of the system; it was strictly a state-by-state process. The roads were strictly state highways that happened to carry ID numbers in cooperation with other states.

They arranged to assign numbers from East to West and from North to South, with lower digit numbers indicating trans-national roads and three-digit numbers indicating alternate (parallel) routes. (When Eisenhower's true Federal highway system was implemented, they numbered them West to East and South to North in the hopes of avoiding a situation where U.S. 50 and I-50 ran near each other, confusing the issue.)

Once the Feds began giving the states money to build feeder roads to the Interstate system, then subsidizing other highway projects, those clear lines of separation between the state and federal highways became blurred, but that is the origin of the two separate numbering systems.

[Duke]

Just as an aside--know what the US highways were called before the Interstates were built?

Interstates. At least according to an old highway map (circa about 1934) I saw in a library. It was actually rather neat to see that a lot of US highways have been re-numbered, no longer exist (Route 66, for example), or are now part of the Interstate system. As but one example of the last, US highway 111, which ran between Harrisburg, PA, and Baltimore, MD, is now part of I-83. From what I understand, it was a two-lane road--during the 70's it was made into a limited-access road and another two-lane section was built right next to it.

[MajorTom]

Wow, learned alot from brianmelendez. Also heard thru the grapevine (not I-5) that the original idea called for at least 1 mile at out of every 20 to be flat, level, and straight to serve as emergency landing areas for planes. (military, commercial?) Also have realized that I-5 on the west coast, to I-95 on the east, all end in "5", while I-10 Southern thru Texas to I-90 thru Montana all end in "0." Mile post markers begin at the southern or western end of the state, with the exception of some states and also with the exception of bypasses which go by the same rule except that the mile markers continue increasing across a state line until the bypass re-joins the main interstate. If I'm anywhere around the bay area, all the above doesn't seem to mean shit.

[Lazlo]

Originally posted by MajorTom
Also heard thru the grapevine (not I-5) that the original idea called for at least 1 mile at out of every 20 to be flat, level, and straight to serve as emergency landing areas for planes. (military, commercial?)

Nope, It's a UL.

[Dogface]

One very important difference, mentioned above but not elaborated upon, is the idea of "limited access". Interstates adoped the Autobahn idea of not permitting any Tom, Dick, and Harry to open his driveway or parking lot directly onto the highway. Likewise, city streets and county roads were not permitted to form direct intersections. Instead, ramp-based interchanges are used. This allows traffic to flow far more smoothly.

As for what the US highways were called before the Interstate system, they were known as "US 70", "US 52" or "Route 52" ("Get your kicks on Route 66"), etc. Many times, the old US route turned out to be a very efficient route to pick, so the interstate was built upon that route, altered to adhere to interstate standards. Other times, there were political pressures to follow or not follow an old route.

[MSU 1978]

Originally posted by tomndebb
One really big difference is that U.S. highways are simply state highways with no Federal input on planning...

Once the Feds began giving the states money to build feeder roads to the Interstate system, then subsidizing other highway projects, those clear lines of separation between the state and federal highways became blurred, but that is the origin of the two separate numbering systems.

They may have been built with no federal input in planning, but the feds certainly have their thumbs in the pie now. As a practical matter, the chief difference is in functional class and funding eligibility. Interstates are functional classes 01 and 11 and are eligible for Interstate Maintenance funds, while US routes cannot be functional classes 01 and 11 and are not eligible for IM funds but are eligible for other federal aid. Federal aid is available for any highway on the federal aid system (i.e, where the functional class is not 08, 09, or 19). In addition, federal bridge monies (HBRRP) is available for bridges on or off the federal aid system.

[MSU 1978]

By the way, the feds do not own the Interstates or US highways, the states do. Few roads are actually owned by the feds, generally they are within national parks or federal forest land.

[NinetyWt]

One beautiful exception being the Natchez Trace Parkway, MSU.

Re: the numbering of interstates: The odd-numbered (I-55, I-65) run north and south. The even-numbered (I-10, I-20) run east and west. Bypass loops add another number to the Interstate being bypassed (I-220).