The last part of the game is a typical rail shooter, at least at the beginning. You can't go anywhere, but what you can do is shoot. The soldiers on the trucks are the most dangerous so eliminate them as quick as you can (#227). Do the same with soldiers equipped with RPGs (#228). When they show up, you will hear it from your teammates.
Then a Hind helicopter with Zakhaev will show up (#229). Try to destroy it with a launcher (#230) - actually there is almost no way you can destroy it now but the helicopter will be distracted. Then the helicopter will fly off. Apparently, Zakhaev will decide that it's better to destroy the bridge instead of the truck.
You survived the crash, but if you don't hurry up you'll die.. Follow Prince to get off the falling bridge and find a suitable position on the road (#231). Kill every opponent you can. The situation is getting worse but hey, you're still alive.
Finally the helicopter will reappear and destroy the fuel tank. When you come round you will see Zakhaev coming with two of his soldiers (#232). Take your chance and, after grabbing the pistol that Price slid to you, kill Zakhaev and his soldiers. After that all you have to do is watch the credits...