- Southern Terminus:
- America's Cup Avenue (RI 238) and Gladys Carr Bolhouse Road (RI 238) in Newport
- Northern Terminus:
- East Main Road (RI 138) in Middletown
RI 138A is a short semicircular route through Newport and Middletown. It begins at the point where RI 238 turns from America's Cup Avenue onto Gladys Carr Bolhouse Road and runs south along America's Cup Avenue for a few blocks before curving to the east to become Memorial Boulevard. RI 138A follows Memorial Boulevard for about two miles and then curves to the north to become Aquidneck Avenue. After about another two miles, it ends at East Main Road (RI 138) in Middletown. The section along America's Cup Avenue and Memorial Boulevard through Newport is a four-lane divided road, while Aquidneck Avenue is a two-lane undivided road.