- Southern Terminus:
- Post Road (US 1) in Charlestown
- Northern Terminus:
- Commodore Perry Highway (US 1) in South Kingstown
RI 1A is a local alternative to US 1 between Charlestown and South Kingstown. It is one of three routes in the state that carry the RI 1A designation. It is designated a north/south route for consistency with US 1, even though it actually runs east and west. It is also designated a scenic route and in many places has special green route shields with the word "Scenic" at the top. Over the course of its length, it touches US 1 twice. The first time, it is multiplexed with the northbound lanes of US 1 for one exit. The second time, it crosses US 1. There is no overpass, so motorists wishing to follow RI 1A must use the turnaround on US 1 to get between the two sections. The portion of RI 1A south of US 1 is known as Old Post Road, while the portion north of US 1 is known as Post Road. The entire length is a two-lane undivided road.