Two wildly incompatible travelers from opposite ends of the personality spectrum are thrust together by a perfect storm of bad mojo, dumb luck and financial roadblocks to embark on a madcap cross-country journey. A marathon of indignities, car wrecks, rough rides in the back of pickups and, of course, hilarity ensues. That describes both "Due Date" (the comedy starring Zach Galifianakis and Robert Downey Jr. that earned $30 million during its first weekend in theaters) and "Planes, Trains & Automobiles" (John Hughes' classic 1987 road romp starring Steve Martin and John Candy).

But just how similar are the two movies? Well, for starters ...

Each film's doddering idiot (Galifianakis' Ethan Tremblay and Candy's Del Griffith) sports curly hair, has lost a loved one and rents a car he'll later destroy while the straight man (Downey's Peter Highman, Martin's Neal Page) snoozes in the passenger seat. Their sacrificial vehicles? Ethan gets a fire-engine-red Subaru Impreza; Del gets a wood-paneled Chrysler LeBaron Town & Country.

The comedy of overweight errors plays out on planes in both movies: In "Due Date," Downey's character gets up close and personal with the short and curlies on Galifianakis' potbelly as he struggles to jam his suitcase into an overhead luggage rack. Meanwhile, Candy's outsize body mass - as well as his foot odor - invades Martin's personal space when the two are jampacked into economy cheap seats in "Planes, Trains & Automobiles."

Both duos have tense pit stops in roadside diners. Ethan complains to Peter that he's "allergic to waffles" after a meal at a Waffle House; Neal attempts to give Del a none-too-subtle kiss-off in a greasy spoon. Then there are the stinging personal indictments. Del to Neal: "Nice personality combination: hostile and intolerant." Ethan to Peter: "What do you have? You have a nice hairline. Fine. You have a strong jaw. But I gotta tell you, mister, your personality needs some work."