I-85 was completed from the S.C. line to Charlotte by 1965, and northwest of Charlotte and Durham in the early 1970s. 

By 1973, I-85 was complete and signed through the entire state. Between Lexington and Greensboro, however, the road was routed further west of the current alignment, over what is now Green 85. This so-called "I-85" was, and still is, only four lanes wide with several at-grade crossings. 

When this original 85 was built through Lexington, plans were already in the works for a bypass: At what is now Exit 87, the original road swung well to the right (east), then turned back left (north) and traversed a "bridge over nothing". The roadway still follows this same route. The bridge indeed had a purpose; it now crosses over today's six-lane I-85. The original roadway was built this way so that a northbound right-hand exit off the "new" (now the current) I-85 could be easily built. 

The six-lane stretch between Lexington (exit 87) and Greensboro (exit 118), several miles east of the original I-85, started construction around 1980 and opened around 1984. While this road was built, the original route was called Temporary 85, and after the new road opened, the old route became Green 85. 

Eight-lane widening through Charlotte, between I-77 (exit 36) and 29/49 (exit 42), opened in mid-1989. Eight-lane widening through Charlotte west of I-77, opened 1990-92. The SPUIs at N.C. 16 and 27 were upgraded from simple diamonds at this time. 

Earnhardt Road interchange (exit 60) opened, 1992[2]. The road existed long before the interchange was built. I'm not ready to believe the road has any connection to NASCAR driver Dale Earnhardt without solid proof. 

Six- to eight-lane widening through Gaston and western Mecklenburg counties, opened in stretches 1993-94. 

Six- to eight-lane widening for the 85/40 multiplex between U.S. 29 in Greensboro (exit 127) and the 85/40 split near Durham (exit 163), late 1980s and early 1990s. This sorely-needed widening required the removal and rebuilding of every overpass, and the realignment of several crossing roads -- the original I-85 was only four lanes and future widening had not been foreseen during the original construction. At all times during reconstruction, two lanes of travel were maintained in each direction. 
Generally, the project was completed first through Alamance County (started 1989, opened 1993-94), then Guilford County (started 1993, opened 1994-95), then Orange County (started 1995, opened 1997-98). [2] 
Near the end of the 85/40 widening project above, the left exit for U.S. 70 (exit 161) was changed to a right exit. 

Completion of the U.S. 220 interchange in Greensboro, 1994[2]. 

Construction of the N.C. 147 interchange in Durham (exit 172) and six-lane widening in the immediate area, completed mid-1998. 

Six-lane widening between Charlotte and the Green 85 split near Lexington (exit 87), started 1997 and continuing now. 

Extension of six-lane portion through Gaston County westward to the interchange with U.S. 74 (exit 10), started August 1998. 

Bypass around Greensboro to the southeast of the current road, 21st century.

At milepost 98, the northbound lanes of I-85 cross under the southbound lanes, and cross back over them near milepost 102. This results in motorists driving on the "wrong side of the road" for three-plus miles: while you're driving this stretch, the opposing lanes are on your right. One reason this was done was to allow right-hand exits for the N.C. Vietnam Veterans' Memorial, which lies in the spread median between the two roadways at milepost 100. There are also two rest areas [1] in the middle of the road here, one serving each direction. Furthermore, the Hamby Creek runs between the two roadways, and engineers may have chosen the switchover design and wide separation to best preserve the creek. 
As a practical matter, the "wrong-way" switch is not very noticeable, because the roadways are separated by several hundred feet of woods in this area. 

The northernmost exit off 85 in South Carolina, exit 105, is signed for Grover, but no signs mention that Grover is actually in North Carolina. 

The bridge over the Catawba River, at the Gaston/Mecklenburg county line, is named the Cameron Morrison Bridge. Morrison was North Carolina's Good Roads Governor, having lead an effort to pave most of the state's major roads during his leadership between 1921 and 1925. Wonder what he'd think of the eight-lane Interstate whose bridge bears his name today. 

In August, 1992, I was traveling 85 while the N.C. Highway Patrol was conducting a peculiar roadblock. A few miles over the Virginia line, changeable message signs read, "DRUG CHECK AHEAD / Be Prepared To Stop." Several miles of driving, no checkpoint. Then an exit appeared, and a squad of troopers was waiting at the end of the off-ramp. Get it? The cops figured that if you had drugs, you'd try to exit. No roadblock was ever set up on the 85 mainline itself. There were no towns or traveler services at the exit in question, so anybody who actually tried to get off was probably presumed guilty until proven innocent. 

I-85 is often invoked as a cheer during ACC Tournament basketball games. (Since 1990, the Atlantic Coast Conference men's basketball tournament has been held in either Greensboro or Charlotte every year. From these two cities, most ACC schools are directly accessible via 85.) When it becomes obvious a team will lose, the winning team's students will often cheer, "85 North! 85 North!" to indicate it's time to hit the road. Of course, if the losing team is Georgia Tech or Clemson, the cheer will be "85 South" instead. 

I-85 is The Official Interstate of the South. Why? First, it serves only Southern states and goes through five of them. Second, it goes through the South's largest city (Atlanta) and serves the metro areas of four Southern capital cities (Montgomery, Atlanta, Raleigh/Durham and Richmond/Petersburg). Finally, it's usually the road one travels to get from "The North" to "The South", especially when starting in the Boston-Washington megalopolis.

Provide mileages on signs for some cities outside North Carolina, such as Atlanta or Richmond. In the late 1990s mileage signs in the Durham area which state the distance to Petersburg first sprouted up; this is a good start. 

785? Why 785? What's wrong with 185, 385 or 585? To use 785 is reminiscent of Georgia's I-985 when that state could have used a lower number. If it's necessary to call this road an Interstate, use 185. Or better yet, 173.