You may wonder why a mainstream movie with such name actors as Mark Ruffalo and as big a star as Joaquin Phoenix never made it to a theater near you. In part it shows that actors are slowly but surely tumbling in their importance in movies. Concept, special effects, product recognition — these are becoming the stars of today. (If you need proof, take a gander at the upcoming “Cloverfield,” in which a giant gimmick attacks a New York strangely bereft of celebrities. It opened with a nationwide release.)

Another reason is that “Reservation Road,” written and directed by “Hotel Rwanda” director Terry George, is pretty weak stuff. “Reservation Road” starts off as an investigation of grief and guilt, along the way looking into the nature of justice, but ends somewhere else. The story concerns a father (Phoenix) and his effort to catch a hit-and-run driver (Ruffalo) who accidentally runs over his young son on the winding road in question, killing the boy instantly. To heighten the suspense, many implausibilities pile up after the accident: The father, Ethan, happens to take his children to piano lessons with the driver’s ex-wife (Mira Sorvino). The driver, Dwight, works at the law firm where Ethan goes to get help with his private investigation. Dwight ends up being Ethan’s lawyer. And so on.

Astonishingly, these contrivances come to nothing.

Ethan visits the local police often, to no avail. They pay him lip service, but give up the search fairly quickly. His wife (Jennifer Connelly), somewhat unbelievably, deserts him as well. These plot elements, as it turns out, also bear little fruit, and they seem inserted only to ratchet up the tension. Perhaps sensing the citrus scent emanating from his vehicle, George soon abandons the drama he’s developed, swerving the story into an action-thriller finale. It’s a road traveled far too frequently by movie endings. “Reservation Road” crashes. (R)