The song is ironic and tragic. The narrator recounts someone close to him (friend, girlfriend; it's unclear) who left the small town they both lived in for the big life in the big city, promising to return someday with many riches, including a big expensive car. But the friend or girlfriend is killed in a car crash ("the papers" reporting about the fatal crash, the race on the highway, the curve they didn't see), and so now, as the narrator tearfully reports, the friend or girlfriend is returning to his/her small hometown in a big expensive car, but not exactly as planned: he/she is dead from the accident, and riding in a coffin in a hearse, the "long black limousine" of the title. The narrator sings that his heart, his dreams, all ride forlorn with the dead friend or girlfriend in that long black limousine.
The song is ironic and tragic. The narrator recounts someone close to him (friend, girlfriend; it's unclear) who left the small town they both lived in for the big life in the big city, promising to return someday with many riches, including a big expensive car. But the friend or girlfriend is killed in a car crash ("the papers" reporting about the fatal crash, the race on the highway, the curve they didn't see), and so now, as the narrator tearfully reports, the friend or girlfriend is returning to his/her small hometown in a big expensive car, but not exactly as planned: he/she is dead from the accident, and riding in a coffin in a hearse, the "long black limousine" of the title. The narrator sings that his heart, his dreams, all ride forlorn with the dead friend or girlfriend in that long black limousine.
[Edit: added on word]