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9.96 miles ; from I-30 to I-40 in Little Rock.
Northbelt extends I-440, but not as an interstate
On January 30, 2003, a five-mile section of the Northbelt freeway, opened between I-40 and US 67/167 northeast of Little Rock. The $63 million, six-lane freeway acts as an extension of I-440 across I-40, but is called state highway 440. 
As of late 2006, a 13-mile section from US 67/167 back to I-40 at I-430 remains to be built. The section through Sherwood is still under discussion, but proponents hope to have a Record of Decision from the FHWA by spring 2007. 
Another issue is funding -- none is available for the Northbelt. Some highway officials are calling for the future segment to be a toll road. (The planned Bella Vista Bypass, an extension of I-540, will be the state's first toll road.) 
The idea of a northern belt for Little Rock dates back to 1941. 
I-440 North Carolina
16.40 miles . Interstate 440 and a portion of I-40 form the 25-mile Raleigh Beltline. This was given the I-440 designation in June 9, 1991, replacing a somewhat confusing system of six different numeric designations. Even the portion of the Beltline overlapping I-40 was included, giving I-440 an initial length of 25.05 miles. 
However, motorists were still getting lost. In 1996 NCDOT posted signs with the new Beltline directional strategy: Inner Beltline (clockwise) and Outer (counterclockwise). This wins points for consistency but loses on clarity; the creation of a separate Outer Beltway (I-540) only muddied the Inner/Outer issue.
In August 2002, NCDOT announced a new convention, which it plans to implement at some point (though nothing has been funded or scheduled). I-440 will be defined along the northern alignment only (between I-40 exits 293 to exit 301), and the overlap with I-40 will be removed. As the remainder will be a mostly horizontal route, I-440 will be signed East and West.  The FHWA route log, where I-440 and I-40 do not overlap, already reflects this change.
Thanks to Steve Moerland for pointing out an error and clarification in the I-440 changes. 
I-440 (numbered as another interstate) Oklahoma
Old number for what is now I-44 between I-240 and OK 66.
7.64 miles ; I-40 to I-24 in Nashville. Proposed for decades, Interstate 440 opened between I-24 and I-65 in 1986, and between I-65 and I-40 in 1987. It's the most expensive road Tennessee had built to that point because of the high profile neighborhoods the road cut through and separated, and the large stack interchange at I-65. Afternoon drivers can delight to the sight of prison labor diligently planting new shrubs and bushes and wildflowers along high concrete soundwalls. 
I-440 is already obsolete: only 4 and 6 lanes wide, it suffers nasty backups eastbound between I-65 and I-24 during afternoon rush hours Widening it will most likely require a complete rebuild of several bridges at the I-440/I-24 interchange. 
You've heard of the Merritt and Bronx River Parkways; well, the 440 has a parkway name as well. On every entrance ramp stands a sign reading "Entering Four Forty Parkway". One of the compromises that helped mollify the opposition enough to get the route built was a ban on tractor trailers, which would have technically made the road a parkway. At some point near the opening of the freeway, TDOT decided it would be safer for traffic to let the trucks use I-440 to bypass Downtown Nashville and its "Truckers Curve" (I-40 westbound flyover ramp at the former I-265 junction). The "Four Forty Parkway" signs still remain, but locals simply call it I-440. 
Majoring in highway law? (It's a growing field.) Refer to Nashvillians Against I-440 v. Lewis, 524 F. Supp. 962 (M.D. Tenn. 1981).