Welcome to Philadelphia. Traffic around City Hall is gridlocked. A motorcycle clips your side mirror and roars away. Garbage trucks are running lights. What else is new?

Um, the swarms of limb-chomping zombies are kind of a fresh twist, aren't they?

Yes, World War Z - a relentless horror thriller that serves up a chilling vision of a planet in the throes of apocalypse - begins in the City of Brotherly Love. (Although, for the record, and for the tax breaks, the Philly stuff was shot in Glasgow.) There's a heartwarming moment first: Brad Pitt busy flipping pancakes for his wife and kids, the news from the TV full of cheer - beached dolphins, out-of-control CO2 emissions, martial law.

By the time the family flees town, Philly is in flames, and there are roadblocks on the Ben Franklin Bridge. Can't let the zombies get to the Cherry Hill Mall.

Pitt is Gerry Lane, a retired United Nations troubleshooter. Mireille Enos, the mopey Detective Linden from TV's rain-soaked noir The Killing, is Karin Lane. The couple throw each other soulful glances, and seem to have their parenting skills down, too.

"Creatures in our bed!" Gerry exclaims in mock fear as his two girls, Connie and Rachel (Sterling Jerins and Abigail Hargrove), clamber atop him in the wee hours, before zillions of far more menacing creatures start plaguing our hero.

On the acknowledgments page of Max Brooks' World War Z novel, the basis for director Marc Forster's breakneck, big-budget genre flick, the author gives a shout-out to George A. Romero, who laid down the template for the modern-day zombie movie with 1968's Night of the Living Dead. And, indeed, there's nothing about World War Z that we haven't seen before (Danny Boyle's 28 Days Later is probably the closest in tone and terror, though certainly not in scale).

But what World War Z does have going for it is Pitt, who proves why he is an undisputed big-screen star. Even when he's being hounded by hordes of the undead, this guy is cool, unflappable, ridiculously good-looking.

Running madly - and driving, and helicoptering, and bicycling and jet-planing - from Philadelphia to Newark to an aircraft carrier off the Atlantic coast to Korea to Jerusalem and then, fatefully, to a World Health Organization lab in Wales, Pitt's Gerry goes looking for "Patient Zero," the source of this devastating pandemic. Once contaminated, the human-turned-zombie throng start leading with their jaws, clacking their teeth, their milky dead eyes bulging like Looney Tunes demons, convulsing, piling on - giant antlike armies that can topple barricades, scale walls, bring down whole cities in the time it takes to, well, watch this movie.

Maintaining phone contact with Karin proves difficult, and by the time Gerry, accompanied by a brave and bee-stung-lipped Israeli soldier (Daniella Kertesz), arrives in Cardiff, things aren't looking terribly promising: The surviving humans have locked themselves into one wing, while four score of zombie scientists have free rein of the B wing, where, if there's any hope at all, hope lies.

World War Z shows no visible signs of the production woes that have dogged the project - and supplied fodder for entertainment reporters and bloggers. Forster and his team have also mastered the discreet edit, leaving a lot of the blood, gore, and zombie slime to the imagination. (It's still a pretty convincingly creepy affair.) And in less than two hours, Enos, cradling her phone and her screen daughters, manages to smile more than she has in three seasons' worth of The Killing. For that, we must all be thankful.

Maybe Karin Lane knows that when her husband says "I'm coming back," he means it.

World War Z *** (Out of four stars)

Directed by Marc Forster. With Brad Pitt, Mireille Enos, Daniella Kertesz, and Fana Mokoena. Distributed by Paramount Pictures.

Running time: 1 hour, 56 mins.

Parent's guide: PG-13 (intense scares, zombie violence, adult themes)

Playing at: area theatersEndText

Contact Steven Rea at 215-854-5629 or srea@phillynews.com, or follow on Twitter @Steven_Rea. Read his blog, On Movies Online, at www.inquirer.com/onmovies.