In earlier FreightWaves Classics articles, information about several interstates that are part of the U.S. Interstate Highway System (IHS) has been provided in numerical order – Interstate 2, Interstate 4, Interstate 5 (Part 1 and Part 2), Interstate 8 and Interstate 10. The next interstate that will be covered in this series is Interstate 11.

But what happened to the interstates numbered 1, 3, 6, 7 and 9?

If an Interstate 1 existed, it would likely be located west of Interstate 5, which currently is the western-most interstate and runs from the U.S. borders with Canada and Mexico.

To understand why, an understanding of the numbering scheme that governs the interstate routes is needed. Each interstate number contains coded information about its direction, geographic location and function:

Direction. Odd-numbered highways (e.g., Interstate 15) run north-south and even-numbered highways (e.g., Interstate 80) run east-west.
Geographic location. Interstate numbers are also ordered from west to east and south to north; Interstate 5 is thus west of Interstate 15 and Interstate 8 is south of Interstate 10.
Function. A hierarchy of interstate numbers reveals each highway’s function. One or two-digit route numbers ending in 0s and 5s indicate primary highways; a number ending in 1, 2, 3, 4, 6, 7, 8 or 9 indicates a lesser interstate; and three-digit numbers indicate spur routes if they begin with an odd number (e.g., Interstate 105) or a bypass route if they begin with an even (e.g., Interstate 405).

The interstate system helps trucks deliver their loads faster and more economically. (Photo: Jim Allen/FreightWaves)

Interstate 1

Because 1 is an odd number, Interstate 1 would run north-south. Also, because 1 is lower than 5, it should be located west of Interstate 5, the lowest odd-numbered interstate in existence. 

In some places along the West Coast, constructing an interstate highway west of I-5 would be nothing short of an engineering miracle. Few highways exist that run through California’s Coast Ranges, the Klamath Mountains, or the Oregon Coast Range. Those that do, like California’s State Route 1, are slow, narrow and curvy.

A heavily traveled stretch of US 101 in Marin County, California. (Photo: Transportation Authority of Marin County)

The only plausible path for Interstate 1 is already occupied by U.S. Highway 101. Perhaps US 101 could become I-1 were it upgraded to interstate design standards. But U.S. 101 runs along oak-dotted hills and through redwood forests. Widening and straightening the highway into an interstate would destroy beautiful stretches of nature. And U.S. 101 serves as “Main Street” for a number of small coastal towns. An interstate would bypass these communities. And in San Francisco, U.S. 101 follows the city’s streets. A new urban interstate would destroy neighborhoods and business districts. 

The major issue with a hypothetical Interstate 1 is the rugged character of the California, Oregon and Washington coasts. Imposition of the Interstate Highway System’s strict design requirements – minimum lane widths, maximum curvatures, maximum grades, etc. – would be very difficult in many areas on the coast of the three states. Interstate 5’s route between the Mexican and Canadian borders is an inland route; it avoids the very difficult terrain along the coast. 

The reasons why there is no Interstate 1 include numbering schemes and engineering challenges – not to mention costs. But a better answer is that an Interstate 1 built west of Interstate 5 would destroy too much of the California and Oregon coasts and coastal communities for little gain to motorists.

The interstates were constructed to carry both automobile and truck traffic. (Photo: Shutterstock)

Interstate 3

Interstate 3 does not exist – yet. I-3 is the proposed designation of an Interstate Highway Corridor under development in the Southeastern United States. If it is numbered I-3 when it is built it will not follow standard interstate numbering – under established numbering conventions, I-3 would normally run west of I-5 along the Pacific Coast. However, noting what is written above about an I-1, building an I-3 to the east of I-1 and west of I-5 is simply impractical.

At this time, I-3 is planned to follow a path from Savannah, Georgia, to Knoxville, Tennessee. The interstate was established by the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) legislation that also created Interstate 14 (which is located in Texas). 

The “Interstate 3” designation has not been officially accepted by American Association of State Highway and Transportation Officials (AASHTO) or the Federal Highway Administration (FHWA), but is being used by the Georgia Department of Transportation and others to identify the highway. 

The reason to number the proposed interstate as I-3 derives from the 3rd Infantry Division, which is based near Savannah at Fort Stewart. Portions of the planned route, including the Savannah River Parkway, are already built to interstate standards; however, the exact route is not finalized, especially across the Appalachian Mountains northwest of Augusta, Georgia.

Driving on an interstate in a sparsely populated area also has its challenges. (Photo: Jim Allen/FreightWaves)

Interstate 6

Apparently, there are no plans for an Interstate 6. It is not listed on the Federal Highway Administration lists of future interstate highways or in any other article about the interstates.

One reason may be that U.S. Route 6 (US 6) is a main route of the U.S. Highway system. Also called the Grand Army of the Republic Highway (to honor the American Civil War veterans association) US 6 currently runs east-northeast from Bishop, California, to Provincetown, Massachusetts. However, US 6’s route has been modified several times. From 1936-64, US 6 ended at Long Beach, California. During that period, US 6 was the nation’s longest highway.

Entering California. (Photo: Jim Allen/FreightWaves)

Interstate 7/Interstate 9

Whether numbered Interstate 7 or Interstate 9, an interstate has been proposed by the California Department of Transportation (Caltrans) that would follow State Route 99 in central California. It would run from the split with I-5 at the Wheeler Ridge interchange north through Bakersfield and Fresno to Stockton. In Stockton the proposed route would head west via the State Route 4 freeway to a terminus at I-5 in the central part of that city. An alternate proposed terminus is located at the I-5/US 50/Capital City Freeway junction in Sacramento. There the future interstate, after continuing north from Stockton along Route 99, would run west along the Capital City Freeway, already an interstate route (unsigned I-305), to connect with I-5, which extends north toward Redding. This also serves as a connector to the existing northern portion of Highway 99. 

The potential interstate’s prospects for upgrades to appropriate interstate standards are tied to  Caltrans’ “Route 99 Corridor Enhancement Master Plan,” which outlines improvements to that route, including capacity and physical improvements.

Due to passage of the SAFETEA-LU federal transportation legislation in August 2005, SR 99 from the Wheeler Ridge interchange to Stockton and beyond to Sacramento was designated as High Priority Corridor 54 and the California Farm-to-Market Corridor. The legislation also designated that the corridor would be a future segment of the IHS.

An article in Roads and Bridges entitled Interstate 2000 suggested that the California 99 corridor between Bakersfield and Sacramento (via Fresno and Modesto) should become “Interstate 7.” However, the article pointed out that upgrading California 99 to interstate standards would “require the elimination of several at-grade intersections, expressway sections and some other reconstruction to bring the highway up to interstate standards.”

California 99 was formerly U.S. 99 before it was reclassified as a state highway. On June 11, 2003, the “California Report” segment on KQED, San Francisco’s NPR radio station, indicated that there was a strong desire in Fresno to locate an interstate highway in or very near the city.  Fresno is the largest U.S. city not served by an interstate highway. However, conversion of the state highway to interstate standards is a major obstacle to this route becoming Interstate 7.

Whether I-3, I-6, I-7 or I-9 are built – and when – is still to be determined. The financial costs of building highways has risen dramatically since the first interstates were built. And there are other issues to consider as well.