Undeniably silly and stretching the limits of credibility beyond all bounds (despite being based on a “true story”), this new film by Tony Scott—who apparently wasn’t satisfied with the sight of a subway train barreling ahead uncontrolled in last year’s “The Taking of Pelham 1 2 3”—now goes a similar route above ground, with Denzel Washington again along for the ride. It’s called “Unstoppable” (which proves, of course, to be inaccurate), presumably only because Andrei Konchalovsky has already used “Runaway Train.” But though far-fetched in the extreme and formulaic to a fault, the movie succeeds as an empty-headed adrenaline rush. It’s pure popcorn escapism, and it works on that level.

Mark Bomback’s script is very loosely based on an incident that occurred in Ohio in 2001, when an unmanned train traveled more than 60 miles in two hours at speeds of up to 47 MHP until a second train coupled onto it and slowed it down so that the engine could be boarded. There were no injuries or close calls. Of course in the Hollywood version the train goes much faster and is far more dangerous, loaded with cars carrying highly toxic cargoes that could cause a “death zone” if they were derailed. And it’s traveling through Pennsylvania towns on its way to the densely populated Stanton, where a steep curve awaits. If it can’t be slowed down before it reaches it, a massive disaster threatens.

But not to worry—Washington is on the case. He plays Frank Barnes, a veteran engineer who’s shepherding another train on the same track. Though he’s already been pink-slipped by the bottom-line budgeting of the line owners represented by smarmy executive Galvin (Kevin Dunn), he succeeds in getting his cars onto a siding just in time to avoid a collision, and then elects to chase down the speeding locomotive and do whatever it takes to stop it. His companion in the cab is trainee Will Colson (Chris Pine), precisely the sort of bright-eyed but inexperienced rookie the company is replacing men of Frank’s age with.

Bomback and Scott wisely keep “Unstoppable” at a modest length; it doesn’t even reach a hundred minutes. And editors Chris Lebenzon and Robert Duffy, working from Ben Seresin’s nice widescreen footage, succeed in keeping the action crisp and exciting. But of course incident is required to pad out the running-time, and some of it is pretty tedious. The hostility of Barnes and his colleagues of similar age toward young whippersnappers like Colson is one example of that, and so are the digressions about the men’s family lives (Barnes is having trouble with his two daughters—who are financing their college tuition by working at Hooter’s, of all places—while Colson is separated from his wife and agonizing over it). The cutaways to the officious Galvin and yardmaster Connie Hooper (Rosario Dawson), as well as Werner (Kevin Corrigan), a federal safety inspector who just happens to be on the scene, are better, but still come across as filler. On the other hand, the material dealing with Dewey (Ethan Suplee), the doofus yard worker responsible for letting the train get away in the first place, works as comic relief.

What really matters, of course, are the big set-pieces that kick in at about the halfway point. There are shots of the train crashing through autos and trucks positioned too close to the track, with people and animals scampering out of the way in the nick of time. There’s a failed attempt at stopping the speeding time bomb—Galvin’s idea—by lowering a man from a helicopter into the engine to apply the brake. But the piece de resistance comes, of course, when Frank and Will go into courageous mode as the train nears Stanton, catching up to it, linking onto it, slowing it down and eventually running along the tops of the cars to reach the locomotive. In the end a pick-up truck driven by another railway employee (Lew Temple) has to get involved in a last-ditch effort to speed an injured Colson to the engine as Barnes raises his arms in a Nixonian victory salute while standing atop a car. (I don’t think it’s too much of a spoiler to reveal that the train does not destroy the town. This is a Denzel Washington vehicle!)

Scott stages all this with the skill that’s expected of him, cannily using TV news reports to explain what’s happening so the viewer doesn’t lose his way, and Washington and Pine play well off one another, even if the banter Bomback provides them with is pretty rudimentary stuff. Everybody else does what’s necessary, if not much more, but Suplee and Corrigan should be singled out for getting some smiles with their goofily understated turns.

“Unstoppable”—which of course eventually refers more to Barnes and Colson than the runaway train—isn’t much more than an action exercise, resembling a summer blockbuster rather than a picture being released in the awards-conscious autumn season. But on that level it works as mindless but well-constructed popular entertainment.