- Washington- 297.52 miles
- Idaho- 73 miles
- Montana- 558 miles
- Wyoming- 207 miles
- South Dakota- 412 miles
- Minnesota- 275 miles
- Wisconsin- 188 miles
- Illinois- 103 miles
- Indiana- 157 miles
- Ohio- 244 miles
- Pennsylvania- 47 miles
- New York- 391 miles
- Massachusetts- 159 miles
- Seattle, WA
- Spokane, WA
- Sioux Falls, SD
- Madison, WI
- Chicago, IL
- Gary, IN
- Toledo, OH
- Cleveland, OH
- Erie, PA
- Buffalo, NY
- Syracuse, NY
- Albany, NY
- Boston, MA
- I-5 in Seattle, WA
- I-82 in Ellensburg, WA
- I-15 in Butte, MT. They stay merged for about 9 miles.
- I-94 in Billings, MT
- I-25 in Buffalo, WY
- I-29 in Sioux Falls, SD
- I-35 in Albert Lee, MN
- I-94 in Tomah, WI. They stay joined until Madison, WI
- I-39 in Portage, WI. They stay joined until Rockford, IL
- I-43 in Beloit, WI
- I-94 in Chicago, IL. They stay joined for a few miles.
- I-55 in Chicago, IL
- I-65 in Gary, IN
- I-94 in Portage, IN
- I-80 in Portage, IN. They stay merged until Clearview, OH
- I-69 in Fremont, IN
- I-75 in Toledo, OH
- I-71 in Cleveland, OH
- I-77 in Cleveland, OH
- I-79 in Erie, PA
- I-81 in Syracuse, NY
- I-88 in Schenectady, NY
- I-87 in Albany, NY
- I-91 in Springfield, MA
- I-84 in Sturbridge, MA
- I-95 in Newton, MA
- I-93 in Boston, MA
- Rapid City, SD- I-190
- Chicago, IL- I-190, I-290
- Cleveland, OH- I-490
- Buffalo, NY- I-190, I-290, I-990
- Rochester, NY- I-490, I-590
- Spur to Corning, NY- I-390
- Syracuse, NY- I-690
- Utica, NY- I-790
- Schenectady, NY- I-890
- Spur to Marlborough, MA- I-290
- Spur to Leominster, MA- I-190
Notes
You can't be the longest Interstate without having a few quirks. In
Montana right by the ID border, I-90 is not a divided highway for a few
stretches. The speed limit there is still "Reasonable and Prudent"
Not only is the I-90 section of the NYS Thruway
marked backwards, with mile numbers going down as you go east, but there
are two metric only signs when you drive westbound. I believe they are
around Syracuse, which is nowhere near Canada.
If you care, I-990 is the highest number given to an Interstate.
I got this email from Brian Marc
Originally from the Syracuse Area, and having a former Thruway Employee as a study hall teacher in high school, here is the legend as to why exit 35 features metric.
The NYSThruway admin decided to test metric sinage (which I am told included [briefly] an 88 km/h speedlimit sign) on the Thruway.
Now the legend part: When one of the metric pushes was on, the state represenative from that district was deadset against it. The Thruway chose his district (Liverpool, next to the former GE plant) as the test site.