Here in the greater Boston area there are several places where there are interchanges for highways that were never finished. I’m thinking of 128 south of Boston, where 95 comes in…there is a cloverleaf there that is only half used, there was a highway that was going to go straight north from there that was never built but the ramps and such are still there. Similarly north of the city where Rte. 3 intersects 128, there are ramps to serve a Rte. 3 extension south that was also never built
Don’t forget the ramps to thin air north of Boston on I-93.
The Southwest expressway was cancled by Gov. Frank Sargent in the '60s, leaving I-95 in the dead end to the south of the city, the inner beltway was killed off, leaving the above mentioned air-ramps north of the city, and a big, already cleared scar through half of the city to the south. Further north, there is another orphened section of 95, so US-1 goes from 4 lanes in each direction, to a local two lane road, while berms run to nowhere in a swamp.
The already cleared land for the Southwest expressway became the right-of-way for the Orange line rapid (?) transit
South of the Park street T stop, the tracks split, with the main line going right, and a abandoned line going left, dead ending where they built the Mass Pike. This chunk may get reused as a part of the silver line bus way.
West of the Arlington St stop, the tracks split, to a sealed up surface portal.
Rhode Island is famous for not removing abandoned bridges, although they did just blow up the old Jamestown bridge.
There is a 3/4th mile long chunk of interstate road/bridge connecting Providence and East Providence. The rest of the road was never built.