It’s not so much a movie as an exercise in cinematic adrenaline, but so long as it sticks to the pavement and avoids trying to humanize its clockwork characters, “Premium Rush” is dumb fun. Unfortunately, especially in the last reel the picture about a daredevil NYC bike messenger who becomes the target of a corrupt cop veers off course and careens into sentimentality. But before that happens, it’s racked up enough mileage to get a pass.

Joseph Gordon-Levitt, continuing his race to action-hero status, is Wilee, the top gun among the ultra-aggressive bikers in a little company run by fast-talking Raj (Aasif Mandvi). He’s having a rough patch with his girlfriend—and co-biker—Vanessa (Dania Ramirez), who feels neglected and is being courted by Wilee’s biggest rival Manny (Wole Parks).

But romantic entanglements turn out to be the least of Wilee’s problems over the course of the evening covered, in nearly real-time fashion, by David Koepp’s flick. He gets a late-afternoon assignment to pick up an envelope from Vanessa’s roommate, Nima (Jamie Chung), a Chinese student, at Columbia and deliver it to a restaurant in Chinatown. He’s almost immediately accosted by Bobby Monday (Michael Shannon), a detective with a hidden agenda, and ordered to turn the envelope over. But Wilee refuses and finds himself pursued relentlessly by Monday.

Why? Because Monday’s in debt to Chinese gambling lords, and his only way to avoid a beating—or worse—is to get the contents of that envelope, which turns out to contain a mysterious ticket issued to Nima by a shadowy crime lord that’s worth a lot of money. How the people Monday’s threatened by knew about the ticket is but one of the many plot holes Koepp and co-writer John Kamps leave hanging, apparently hoping that that the sheer speed with which Koepp, as director, and his agile young cast (as well as a small army of stuntmen) fly over them. And why sweet Nima’s gotten involved with these shady characters is what detours things into schmaltzy territory toward the close.

But despite the plot’s speed bumps, “Premium Rush” still builds up a good head of steam over the course of its ninety minutes, with Koepp using some nifty devices—like a combination of animation and live-action to show Wilee calculating the best route for him to take through heavy traffic—to keep the rush going. He and Kamps add another amusing element to the mix in the person of a NYC bicycle cop (Christopher Place) who becomes obsessed with catching Wilee, to no avail. It’s a pity he has to slow down for flashbacks to explain the rationale behind what’s happening—and to stroke our heartstrings—but if he didn’t we’d remain entirely in the dark.

The role of Wilee doesn’t stretch Gordon-Levitt’s acting chops to any extent—this fine young actor has tackled much meatier parts in the past—though it certainly shows off his physical prowess. But he shows a willingness to make the messenger an unpleasantly cocky fellow through most of the running-time, though in the end he proves to be a softie. Shannon, whose revelatory turn in “Take Shelter” went criminally unnoticed at awards time last year, gets the opportunity to go wild and wacky here; he’s not remotely recognizable as a human being, but his cartoonish overacting is perfect for a character that’s really a live-action Wile E. Coyote frantically chasing Wilee’s Road Runner. Nobody else makes a great impression (save for Place as that luckless bike cop), but Ramirez is attractive and Parks makes a very convincing jerk. More important contributions are Mitchell Amundsen’s slick cinematography, the crisp editing by Derek Ambrosi and Jill Savitt, and David Sardy’s supportive score.

“Rush” might not actually be premium grade, but until it goes syrupy toward the close, it’s an engagingly wild ride.