Former US Route 99 in Atwater originally traversed the City via Atwater Boulevard. Interestingly Atwater Boulevard was replaced surprisingly early on (especially considering Merced wasn't bypassed until 1964) with the titular "Atwater Bypass" realignment of US Route 99 which opened in October of 1957. Given the age of the Atwater Bypass it is now wonder that CA 99 through Atwater is one of the most substandard and rough sections of freeway in the Central Valley.
https://www.gribblenation.org/2021/01/former-us-route-99-on-atwater-boulevard.html