Interstate Frontage Roads

To Which System Do They Belong?

FHWA frequently is asked whether interstate frontage roads are included in the Interstate System or the National Highway System (NHS).

The general answer is "no."

However, there are a number of cases where a partial exception to, or expansion of, or addition to this answer is appropriate.

Important partial exceptions include the following:

• In some cases, a portion of the frontage road serves as part of an Interstate ramp.
• In some cases, a portion of an Interstate frontage road is on a bridge and the substructure of the bridge (or a portion of it) carries both the frontage road and the mainline Interstate and thus the bridge as a whole might be considered an Interstate Bridge.
• The edge of the Interstate Right-of-Way is a factor in Outdoor Advertising regulations (23 CFR 750.152, etc.) These regulations require control of all signs within 660 feet of the outside of the Interstate facility. In most cases, FHWA accepts the definition of the Interstate Right-of-Way established by the State Department of Transportation (there may be some unusual cases in which the FHWA does not accept this).

Important expansions to the general answer include the following:

• In some cases, e.g., where the frontage road is part of the Interstate ramp, NHS funds may, after examination and on a case by case basis, be used to improve that section of the frontage road.
• In some cases, Interstate Construction funds may have been used to improve portions of the frontage road when the Interstate was constructed because those portions were important to operation of the Interstate or were a mitigation of the impact of the Interstate (or were used as a detour route during construction of the mainline).
• While the Interstate frontage roads are not considered part of the Interstate system for the purpose of application of the vehicle weight and length provisions of Section 127 of Title 23 U.S.C., many sections of Interstate frontage road are, in effect, the access to the Interstate system and thus fall under the "Reasonable Access" part of these provisions.

Important additions to the general answer include the following:

• Notwithstanding the use of federal aid highway funds for improvement of frontage roads as noted above, the frontage road may generally be functionally classified as a local road.
• The FHWA does not have a list of the sections where such classifications have been made. Functional classification is essentially an activity of the State Department of Transportation.
• In general the FHWA records hinge on the centerline. The length of the Interstate centerline is used in the determination of NHS mileage (per Section 103 of title 23 U.S.C.) and the determination of apportionments of federal aid funds (per Section 104 of title 23 U.S.C.).

The FHWA realizes that this answer may be disappointing in that some people feel the answer to the question "Are Interstate frontage roads part of the Interstate or the NHS?" should be short and simple.

However, the fact is that the answer must take account of textual differences in different parts of highway statute and regulations, the real world function and operation of frontage roads and other factors.