Tony Scott's films, at their worst, are shallow, shiny baubles, all incident and no meaning, aiming to distract the audience by deadening them with a non-stop assault of noise and flashy images. This also describes Tony Scott's films at their best. The difference between the two poles is one of incredibly subtle degree, and also tone: the less a Tony Scott film has to say, the more fun it is, generally speaking.

Unstoppable, which claims to be "inspired" by a true story - meaning that a true story happened and some of the details accidentally found their way into the shooting script, despite writer Mark Bomback's best efforts - has damn little to say, and is as a result his best film in a whole lot of years: in fact I must go so far back, past the DΓ©jΓ  Vus and Dominos, that we eventually get to movies which I haven't seen in so many years that I do not trust my memory of them. There is a train; it is going extremely fast; it is devoid of people onboard who might stop it; and so it must and can only be stopped by Denzel Washington, the muse of Scott's late-period cinema (this is their fifth collaboration, the forth since 2004). To make certain that we are impressed with the gravity of the situation, there is a train filled with schoolchildren in the runaway's path; once they have been saved (unexpectedly early, at that), they're replaced by the inhabitants of the fictional Stanton, Pennsylvania, a bustling city with a creaky patch of elevated freight track that makes a sharp right-angle turn just over an industrial lot filled with giant fuel tanks. Also, the train itself is toting several thousand gallons of flammable glue ingredients. You can't make this stuff up. Okay, you can, and if you are Mark Bomback, then you did.

The absurdly elevated stakes are just one of the many ways in which Unstoppable takes a few purposeful strides right up the edge of camp, though it always carefully avoids diving over. No, it is tremendously sincere, even while it plays every hoary old card in the book: the sagelike old railroad veteran, Frank Barnes (Washington), who is teamed up with the snotty neophyte, Will Colson (Chris Pine); the protracted moments of quietude in which these two men bond uncertainly by sharing their broken life stories (Barnes has a dead wife and teenage girls whom he's never there for, working their way through college at Hooters - arguably the film's weirdest and most hilariously unclassy touch - while Colson's wife has filed a restraining order against him, for being an impulsive, irrational hothead with a gun, and since this is a Tony Scott film and thus needs its dose of queasy morality, it would appear that we're meant to side with him since it was all just a misunderstanding); the agitated bureaucrat trying to make everything hold together and find a solution, Connie Hooper (Rosario Dawson), while squaring off with her venal but not exactly evil corporate overlord (Kevin Dunn); and cartoon dialogue delivered with an admirable straight face by everyone involved, though you expect that they broke up laughing the second the cameras cut.

And since this is a Tony Scott film, those cameras must have cut quite a lot. Working with editors Chris Lebenzon and Robert Duffy, Scott will never show an action in one shot when he can show it in four; nor is he interested in passing up any opportunity to crash from one potent bit of frenzied business to another, even more frenzied bit someplace else. Even in the quietest moments, the film is constantly moving (befitting the fact that the main action is set on a train), giving you no time to stop and ponder what the hell is happening, and that's just well, since it's obviously stupid.

Here, though, is the rub: nobody involved cares that it's stupid. They revel in it, and are proud of it, and at the very least, Unstoppable is therefore honest. It's an adrenaline rush that lasts exactly as long as the film's running time, and evaporates in the light of day; but what a rush! Breakneck action films are hardly rare, but when they are done extremely well, they're a sublime treat, like eating too many doughnuts in one sitting and then enjoying the resultant stomachache as exactly what you get from indulging in that much fat and sugar. Unstoppable is done extremely well: it doesn't let up, and Ben Seresin's cinematography (you probably don't remember him as the DP of the sinfully ugly Transformers: Revenge of the Fallen, because why on earth would you?) proves to be a perfect match for Scott's music video/TV commercial approach to filmmaking, with flinty colors and just slightly more contrast than your eye quite knows what to do with, and a beautiful veneer of dirty grain that reminds us, blissfully, that this was indeed shot on celluloid.

And when all is said and done, even if the film's charm is largely ephemeral and pulverizing, it is grounded in a realist sensibility that Scott and Bomback do not foreground, and are perhaps even partially unaware of: there is a palpable level of economic paranoia undergirding the whole of Unstoppable, with the initial conflict between Barnes and Colson largely a manifestation of the fear of the gifted, skilled old worker at being pushed out be a cheaper replacement. Financial uncertainty keeps poking through every moment: every important character has to consider the possibility of being fired, and even the icky businessmen who make all the wrong decisions and make the situation worse than it has to be, only start acting icky when faced with a grim $100 million price tag for doing the right thing at the right time.

The film is thus entirely of 2009, the year in which it was shot and in which it is explicitly set; it is a thriller in which only the immediate threat of a million tons of screaming locomotive can shove aside the deeper concern that one patch of bad luck can leave any of us without enough cash to make it to tomorrow. As I said, this is not a theme given very much emphasis, and it's not ultimately very important to the movie's overall functionality; but it is as ever the privilege of the tawdriest genre films to tell us more about life in these modern times than a self-aware dramatic treatment of the same themes. Unstoppable is clearly mindless, but not as much as it thinks it is.