There are only two with bright yellow stripes.
These are the most common and obvious species seen throughout Western Massachusetts. While only two snakes really fit into this category, other snakes have one longitudinal stripe running the length of their bodies, though these are neither yellow nor distinct.
The Gartersnake and Ribbonsnake are the Western Mass snakes with two yellow stripes. Certainly the Gartersnake is familiar to almost anyone who has something more than a parking lot for a backyard or has ever taken even a short walk into a natural area some springtime day.
Gartersnakes come in a fascinating and complex array of species, subspecies, and local forms throughout North and Central America. For the best review, get (and read) The Garter Snakes by Rossman, Ford, and Seigel. Not all Gartersnake forms have stripes, but most do (and so do a lot of other snakes). There is something about that feature that makes Gartersnakes among the most widespread, abundant, and interesting animals in the New World.
Observations of fleeing snakes show that stripes are important markings that confuse visual predators. Stripes act as bright beacons, but as anyone who has tried knows, stripes (and the snake) quickly disappear in the dried grasses, stems, and duff in an upland meadow. To enhance the effect, Gartersnakes typically retreat in a fairly straight path making those thin, yellow lines nearly impossible to track.