Road trips "within" a state that take you out of state

[cl94]

Building off of OP's original example, there is a MUCH shorter example through the same area. The fastest route from the MD 210 corridor south of Washington to pretty much anywhere in Maryland west of the MD 97 corridor involves taking the Beltway around the west side of Washington. For example, National Harbor to Bethesda. This, of course, requires passing through DC and VA.

[Bickendan]

US199 adds a couple of unique situations.  To get from Crescent City to anywhere along I-5 north of Redding, one would use US199 passing through Grants Pass, Oregon.  On the other hand, a trip from Grants Pass or Medford, Oregon, to coastal Brookings/Harbor, Oregon would take you on US199 through the Crescent City area.

Another one I encountered on a road trip was Hood River to Astoria, OR.  Google suggested we cross into Washington on I-205, then cross back south into Oregon at Longview, WA.

Echoing this, Portland to Clatskanie.

Point Roberts to anywhere else in Washington.
And, a technicality: Ferries between North Saanich (Victoria) to Tsawassen (Vancouver) clip through the corner of the Canada/US border.

Finally, an example that satisfies the multi-state condition of the OP: Puducherry, India.

[KCRoadFan]

This applies to certain trips within the KC area -  one way to get from parts of south KC (e.g. Ward Parkway area) to Platte County is to take 435 west to 69 north to 35 north to 635 north, going through Kansas.

As for me, personally, l live in Midtown KC (West 39th Street area) and I've spent many a hot summer day cooling off at an aquatic center off 29 near Zona Rosa and KCI Airport. There are a number of ways to get there, but one thing I've done is to head west on 39th to Rainbow Blvd by KU Med, then proceed north on Rainbow (which becomes 7th Street) through KCK, until it crosses the river on the Fairfax Bridge, near Argosy Casino, and merges onto 635 north, which in turn merges onto 29 north. That route does have a lot of traffic lights, but because it's a more direct route than crossing the river on 35 north, which swings east while the waterpark is northwest (and 35 is often prone to congestion anyway), it's a way that I find practical.

[Sctvhound]

Not many of these in South Carolina, but one is going from Gaffney, SC to North Myrtle Beach or Little River. The suggested routing takes you across US 74 in North Carolina, then the south loop of I-485 around Charlotte, then 85 back into SC. It's 4:05.

[bwana39]

Foreman AR to Texarkana AR (and points farther including Little Rock etc.) You go through New Boston TX. Not a big difference anywhere south of DeQueen.

[Roadgeekteen]

When I was staying at Wyndham Bentley Brook in Hancock, MA, we would often use NY 22 to get to Tanglewood, and, well, just about any other part of Massachusetts. Quicker than driving through Pittsfield.

[Occidental Tourist]

St George, UT to Kanab, UT takes you into Fredonia, AZ.

[hbelkins]

A number of people in the Henderson, Ky. area who are going to Louisville or points east will take I-64 through Indiana instead of US 60 or the Kentucky parkways.

[jp the roadgeek]

When I was on a school tour in 9th grade, the quickest way from Lakeville, CT to Kent, CT was to go into NY by going down CT 41 to Amenia Union, following Dutchess CR 2 to CR 3, which turns into CT 341 to Kent. 

[doorknob60]

Right now, the only way to get from southern Idaho to Northern Idaho (Riggins or anywhere north), on a paved road, is by going through another state. The only real link, US-95, is currently closed south of Riggins due to a landslide. There is no detour route. Some brave folks have taken some back roads from McCall to Riggins, but that's unpaved narrow mountain roads, and apparently they may have closed that too after some accidents up there. Google Maps shows a parallel route, Pollock Rd, as an alternative, but that's been permanently closed for years (you can see concrete barriers on Google Satellite view). The only realistic detour involves going through Washington and Oregon, or Montana, depending on where you're coming from/going.

[mgk920]

Most anywhere of consequence in Wisconsin and Florence, WI.

Mike