The Hangover director Todd Phillips has just signed Robert Downey Jr. to star opposite his Hangover scene-stealer Zach Galifianakis in the comedy Due Date, which could begin filming as early as the fall. While the film has not yet been greenlit by Warner Bros., the studio is close to pulling the trigger, and bringing Downey on board will certainly accelerate the pace. The project centers on an expectant dad, to be played by Downey, and his unlikely travel companion (Galifianakis), who race cross-country in hopes of making it home in time for the birth of his first child. (Think Planes, Trains and Automobiles with Downey in the straight-man Steve Martin role.) Due Date was written by Alan R. Cohen and Alan Freedland, with a revision by Adam Sztykiel. Warners would ideally like to release the film next summer, taking a similar box office route to The Hangover, which has now grossed more than $240 million.