While Arnold is getting up (and a guy with a camera is getting many pictures), John runs down the stairwell to his bike, has the requisite trouble starting it, and vrooms off. Robert follows on foot, and his compact running style looks like it could do thirty or forty mph easily. John pulls out in front of a semi, which Robert jumps into and commandeers, and before you know it, we're in the middle of an action sequence!
So: Robert's driving a Freightliner with reckless abandon, knocking cars out of the way in his pursuit of John, who's driving a wee little motorcycle. The chase goes down a reasonably busy street, at which point it picks up Arnold on his large motorcycle, and John goes down into the concrete thing that looks like the scene of the race from Grease. Only the wee motorcycle can make it down the path he chose, so John thinks it's safe to stop and look behind him. When he sees the Freightliner go flying off the overpass and come lurching forward at him, all crushed and broken but still going faster than he can, John sensibly takes off again. He weaves around puddles, shopping carts, and derelict cars, while Robert drives right through them. Arnold follows up above them (where the Pink Ladies were sitting in Grease), taking the occasional pot shot at the truck. A low overpass does not deter Robert, who cheerfully lets the top of his truck get sheared off. After Robert's truck rams John a few times (which I would have thought would be hard for a kid on a small motorcycle to handle), Arnold flies his motorcycle down the twenty feet or so to get involved in the chase on a personal level. After managing to get around the Freightliner, Arnold scoops John onto his bike and shoots out one of the truck's front tires with his shotgun. If this were The A-Team, the truck would immediately flip over, but instead it slides out of control into a pillar. In an uncharacteristic nod to realism, we're shown both the spewing gas and some sparking wires before the inevitable explosion. Arnold readies his shotgun, but the only sign of life is a pretty cool burning tire rolling out of the wreckage. He and John speed off. And then, of course, a shiny silver man walks out of the fire, resolving itself into Robert Patrick.