The bridge is indeed deserted. It may be dilapidated, but it's still strong enough to carry your vehicles (one at a time). The old wooden shack contains nothing of value.

The rumble of truck engines in the distance is a red herring. It could be an unusual echo, or the sound of other US forces, enemy trucks or civilian vehicles. Throw a D6. A score of 1 means they've been spotted. It's a 50/50 chance whether this is good (the US forces are welcomed as liberators) or bad (they are regarded as imperialist aggressors). Throw a D6. On a score of 1, a US soldier thinks he heard someone/something watching them. In either event, the US player should see no one. There may be the nagging doubt that they've been seen, but that's all.