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U.S. Route 20 is the longest highway in the United States at 3,365 miles, running from Boston, Massachusetts, to Newport, Oregon. That is longer than Interstate 90, the longest Interstate, which spans about 3,020 miles between Seattle and Boston. This ranking separates U.S. Routes from Interstates because they are different systems, with different numbering, standards and histories.
Mileages are rounded and can change when route endpoints or alignments are revised. The first six positions below are supported by current federal or compiled route data; exact current mileages for positions seven through eleven should be checked against the latest Federal Highway Administration (FHWA) Interstate Route Log.
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The 11 longest U.S. highways
| Rank | Route | System | Approximate length | Endpoints | Orientation | Source status |
|---|---|---|---|---|---|---|
| 1 | U.S. Route 20 | U.S. Route | 3,365 miles | Boston, Massachusetts, to Newport, Oregon | East–west | FHWA, 2025 route information |
| 2 | Interstate 90 | Interstate | About 3,020 miles | Seattle, Washington, to Boston, Massachusetts | East–west | Compiled route table retrieved in 2026 |
| 3 | Interstate 80 | Interstate | About 2,899 miles | San Francisco, California, to Teaneck, New Jersey | East–west | Compiled route table retrieved in 2026 |
| 4 | Interstate 40 | Interstate | About 2,559 miles | Barstow, California, to Wilmington, North Carolina | East–west | Compiled route table retrieved in 2026 |
| 5 | Interstate 10 | Interstate | About 2,460 miles | Santa Monica, California, to Jacksonville, Florida | East–west | Compiled route table retrieved in 2026 |
| 6 | Interstate 70 | Interstate | About 1,337 miles | Cove Fort, Utah, to Baltimore, Maryland | East–west | Compiled route table retrieved in 2026 |
| 7 | Interstate 95 | Interstate | Not stated in the available current table | Not stated in the available current table | North–south | Verify against the current FHWA Interstate Route Log |
| 8 | Interstate 75 | Interstate | Not stated in the available current table | Not stated in the available current table | North–south | Verify against the current FHWA Interstate Route Log |
| 9 | Interstate 35 | Interstate | Not stated in the available current table | Not stated in the available current table | North–south | Verify against the current FHWA Interstate Route Log |
| 10 | Interstate 94 | Interstate | Not stated in the available current table | Not stated in the available current table | East–west | Verify against the current FHWA Interstate Route Log |
| 11 | Interstate 5 | Interstate | Not stated in the available current table | Not stated in the available current table | North–south | Verify against the current FHWA Interstate Route Log |
The table ranks named mainline routes, not every state highway, business loop, spur or auxiliary Interstate. “About” indicates a rounded figure rather than a permanently fixed mileage.
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U.S. Route 20 crosses the northern United States from Boston to the Oregon coast for 3,365 miles. FHWA identifies it as the longest U.S. road. Its route includes two non-contiguous sections in Yellowstone National Park, where the U.S. Route 20 designation is interrupted rather than carried continuously through the park.
#1 Best Overall
U.S. Routes were organized in the 1920s. Major east–west roads generally received numbers ending in zero, which is why U.S. 20 occupies a prominent cross-country corridor. The system is not built to one uniform freeway standard: sections of U.S. 20 are divided highways, ordinary two-lane roads and urban streets.
Is U.S. 20 longer than I-90?
Yes. At 3,365 miles, U.S. 20 is roughly 345 miles longer than I-90’s approximately 3,020 miles. U.S. 20 also begins farther east, in Boston, while I-90 begins in the Seattle area and terminates in Boston.
Rank #2
The comparison is not a contest between identical road types. I-90 is a controlled-access Interstate designed for high-speed, long-distance movement; U.S. 20 is an older numbered route whose segments vary substantially in design and speed.
The longest Interstate highways
Interstate 90
I-90 is the longest Interstate, crossing Washington, Idaho, Montana, Wyoming, South Dakota, Minnesota, Wisconsin, Illinois, Indiana, Ohio, Pennsylvania, New York and Massachusetts. The compiled route table used for this ranking lists approximately 3,020 miles.
Rank #3
- Road Atlas, Adventure Edition
- Road Atlas, Adventure Edition
- National Geographic Maps
Interstate 80
I-80 runs about 2,899 miles from the San Francisco area to Teaneck, New Jersey. It is a major transcontinental route across the northern half of the country.
Interstate 40
I-40 covers about 2,559 miles between Barstow, California, and Wilmington, North Carolina, paralleling or replacing portions of historic U.S. 66 across much of the Southwest.
Interstate 10
I-10 stretches about 2,460 miles from Santa Monica, California, to Jacksonville, Florida. It is the southernmost transcontinental Interstate and crosses the country’s southern tier.
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Interstate 70
I-70 is listed at about 1,337 miles from Cove Fort, Utah, to Baltimore, Maryland. It crosses the Rocky Mountains and the central United States but is considerably shorter than the four Interstates above it.
Best Value
- Teach geography using the Rand McNally United States Interstate Fold Map. This folded interstate map is complete with clearly indicated cartography and points of interest.
- Folded map features all Interstate and U.S. highways.
- Clear, easy-to-read cartography.
- Clearly indicated cities, points of interest, airports, boundaries and more.
- Measures 9-1/2" x 4".
Why highway mileage changes
Route length depends on the official endpoints and the alignment recorded for a particular year. FHWA records that U.S. Route 6 once measured 3,652 miles. After California moved its western terminus to Bishop, the route became shorter; historical figures for U.S. 6 are also reported around 3,227 to 3,249 miles in different records. That change left U.S. 20 as the longest U.S. road.
Consequently, a ranking should always show its mileage date and source. Construction, endpoint changes, rerouting and corrections can alter a route’s listed length without changing its familiar number.
What makes an Interstate different?
The Interstate Highway System has a distinct national transportation and defense purpose. FHWA describes Interstates as controlled-access roads built to common standards, including standardized lane dimensions, limited access points and connections among major cities and strategic corridors.
That design makes an Interstate more consistent for through travel than a typical U.S. Route, but the route number alone does not tell you the exact driving distance. Bypasses, metropolitan approaches, overlapping designations and endpoint definitions can produce different totals among mapping services.
How large is the U.S. road network?
FHWA’s 2026 overview reports about 4.2 million miles of public roads in the United States. The Interstate system accounts for approximately 48,830 miles, plus 286 miles in Puerto Rico. The longest routes therefore represent only a small fraction of the national network.
Quick Recap
Planning a cross-country drive on the longest routes
- Use the route number as a starting point, then confirm the current alignment in state transportation maps or a live navigation service.
- Allow extra time on U.S. 20: its non-freeway sections, towns and variable speed limits make travel times very different from an Interstate calculation.
- Check seasonal closures, especially across mountain passes and in or near national parks.
- Treat the mileage figures as route lengths, not a promise that a single uninterrupted drive is possible; construction, park interruptions and local detours can change the actual trip.
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