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What Is The Longest Interstate In The U.S.?

The longest interstate in the United States is Interstate 90 (I-90), which crosses the upper quadrant of the country, starting in Boston in the East and continuing to Seattle in the West.

The eastern terminus lies less than ½ a mile from Boston Harbor, while the western terminus lies roughly the same distance from Elliott Bay, meaning I-90 comes within a mile’s access to both the Atlantic and Pacific Oceans.

It truly is a coast to coast highway.

How long is Interstate 90?

Interstate 90 has a total distance of 3,021 miles (or 4,862 km).

What states does Interstate 90 go through?

Interstate 90 passes through 13 states.

Those states are:

  • Massachusetts
  • New York
  • Pennsylvania
  • Ohio
  • Indiana
  • Illinois
  • Wisconsin
  • Minnesota
  • South Dakota
  • Wyoming
  • Montana
  • Idaho
  • Washington

How long is I-90 in MA?

138 miles

How long is I-90 in NY?

386 miles

How long is I-90 in PA?

46 miles

How long is I-90 in OH?

243 miles

How long is I-90 in IN?

156 miles

How long is I-90 in IL?

108 miles

How long is I-90 in WI?

187 miles

How long is I-90 in MN?

276 miles

How long is I-90 in SD?

413 miles

How long is I-90 in WY?

210 miles

How long is I-90 in MT?

554 miles

How long is I-90 in ID?

74 miles

How long is I-90 in WA?

298 miles

Which cities does Interstate 90 go through?

Along with its terminus cities of Seattle and Boston, Interstate 90 passes through (or on the outskirts of) multiple large cities. (For the sake of this article, we’ll define large cities as those with 100,000 or more residents.)

These cities are:

  • Springfield, MA
  • Syracuse, NY
  • Rochester, NY
  • Buffalo, NY
  • Cleveland, OH
  • Toledo, OH
  • South Bend, IN
  • Chicago, IL
  • Rockford, IL
  • Madison, WI
  • Rochester, MN
  • Sioux Falls, SD
  • Billings, MT
  • Spokane, WA

Interstate 90 also passes through multiple smaller cities, including:

  • Framingham, MA
  • Worcester, MA
  • Albany, NY
  • Utica, NY
  • Erie, PA
  • Gary, IN
  • Rapid City, SD
  • Bozeman, MT
  • Missoula, MT
  • Coeur d’Alene, ID

Other Notable Places Along Interstate 90

Along with the cities it goes through, Interstate 90 passes several notable attractions or towns.

These include:

  • October Mountain State Forest (Appalachian Trail Head)
  • Lake Erie (rolls right over it in Cleveland)
  • Notre Dame University
  • Badlands National Park
  • Black Hills National Forest
  • Sturgis, SD (known for its motorcycle rally)
  • Bighorn National Forest
  • Mt. Baker-Snoqualmie National Forest

How long did it take to build I-90?

The majority of Interstate 90 took 31 years to build. It was first commissioned in 1956 and made it all the way across the country by 1987.

But it was extended further into Seattle in 1993 and further into Boston in 2003.

So, all in, I-90 as it runs today was built between 1956 and 2003 and took 47 years to complete!

How long does it take to drive I-90?

With speed limits factored in, it takes approximately 45 hours to drive I-90 from one terminus to the other, or almost two full days if you drive straight through. (We’ll assume here you have a very comfortable car and an extra driver.)

But that doesn’t take into account traffic (you will definitely encounter some), fuel stops (you’ll need a few), or any other stops you’ll want to make along the way (there’ll be plenty).

So, cutting back to a far more reasonable eight hours per day of driving, you’re looking at nearly six days of quality road tripping along the U.S.’s northernmost cross-country interstate.

Want to know about the country’s longest highway, see What Is The Longest Highway In The U.S.?

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