US 117 and SC 38 Myrtle Beach to Latta 1933 Official

US 501 replaces US 117 and SC 38 1935 Official

Adjustments: In April 1937 (SCDOT), US 501 was removed from today's S-26-14 just east of Conway, leaving behind SC 90 ALT.
In 1949, US 501 was given a direct route from Myrtle Beach to Conway, replacing SC 503. The old routing via Socastee became part of SC 544 and all of SC 707. Today this is: S-26-272 Washington Ave; SC 544; Dick Pond Rd; SC 707; Emory Rd/Powell Lane; abandoned routing through the airport; S-26-15 Old Socastee Hwy.

SC 503 appears in eastern Horry County 1940 Official

SC 503 replaced by US 501 corridor 1949 Official

In 1951, US 501 was rerouted in Conway to use S-26-26 9th Ave to Pine St west, then replaced S-26-46 from Conway west to today's S-26-62, then on new construction over to Aynor. The old route remained US 701 to Homewood, and SC 319 over to Aynor.

US 501 Aynor to US 701 1950 Official

US 501 Aynor to US 701 1951 Official

In 1959, US 501 received its current bypass of Conway, leaving behind US 501 Business. 9th St and Pine St were removed from the primary system as 501 Business was routed via 16th St.

US 501 through Conway 1952 Horry County

US 501 Business through Conway 1962 Horry County

About 1970, US 501 was removed from S-17-630 at the North Carolina border to facilitate its interchange with I-95.
In 1990, US 501 received its Marion Bypass.

US 501 through Marion 1987 Marion County

US 501 Business through Marion 1995 Marion County

Improvements: Fully paved when assigned in 1935.
The first multilane section of US 501 was the Conway Bypass and south to Myrtle Beach, in 1959.
The next section to be upgraded was Latta to Dillon, between 1968-69.
In 1974, US 501 was 4-laned from Marion to Myrtle Beach except over the Little Pee Dee River, including an interchange at SC 41.
In 1976, US 501 was multilaned over the Little Pee Dee River.
When the Marion Bypass opened in 1990, it was multilaned, with an interchange at US 76 and on both ends.
In 2007 or 2008, US 501 was multilaned from SC 38 to the Marion Bypass.
In recent years, US 501 was upgraded to expressway with no lights from US 17 Bypass out to at least SC 31. The area just west of the Intracoastal Waterway was always very congested prior to this upgrade.
Comment: US 501 is the main route to get to Myrtle Beach from points west, though with the addition of SC 22, traffic should be more spread out.
US 501's old crossing of the Intracoastal Waterway was on a drawbridge that was shared with the railroad, which is still there (albeit closed to auto traffic).
Another 501 oddity nearby is the ramps from the US 17 interchange have at grade railroad crossings.