Originally, NC 55 ran from US 421 in Erwin (Harnett County) north across the original NC 50 (today's Salem St. in Apex) and north to Durham.

The route from US 64 south has not changed since the road was first signed in the early '30s, but originally NC 55 ran west of its current alignment, including a short multiplex with US 64 around the Wake/Chatham border. It's probable that it ran over what is today NC 751 in Chatham and Durham counties, since the eastward shift of 55 took place around the time 751 was extended south to US 64, but there's an outside chance that 55 could have moved twice: once to Green Level Rd, a mile or so west of the current alignment, then a few years later eastward again to where it is now.

In any case, 55 north of Apex was not paved until it moved off the current 751 alignment.

At some point 55 was moved onto a straighter alignment north of the community of Carpenter; the old alignment is now known as Petty Farm Rd and Alston Ave. No map gets that detailed to know when that happened.

55 is western Wake County's Main Street.  A widening project from US 64 all the way north into Durham County was finally completed early in 2007, with a first-of-its-kind funding process to pay for the widening through west Cary:  the town actually paid for the widening up front, with the state reimbursing the town from the Transportation Improvement Plan as money became available (when it was originally planned to be spent).  That's how badly this road needed extra lanes; even four lanes isn't enough.  While 55 is a lot better now than it was when it was a two-lane road into RTP, it can still be a very slow ride at rush hour.

A 4-lane bypass around Holly Springs was opened in late 2002, and a five-lane widening from the north end of the bypass to US 1 was completed in 2004.  However, thanks to a railroad underpass that will require a reconstruction in any future widening, it's doubtful that 55 will be widened through the town of Apex in the foreseeable future.