Final answer:
You should stop before railroad tracks whenever a train might be approaching. Staying back from moving trains is important due to the atmospheric pressure changes they cause, which could push someone towards the train.
Step-by-step explanation:
You should stop before crossing railroad tracks any time a train may be approaching, whether or not you can see it. It's important to be cautious because trains move quickly and may not be able to stop in time to avoid a collision.
It is dangerous to stand close to railroad tracks when a rapidly moving commuter train passes. This is due to the phenomenon of atmospheric pressure, which can create a low-pressure area around the fast-moving train. As the train passes by, the difference in pressure can push you towards the train. Standing back at a safe distance is essential for safety.
When considering if it's safe to cross tracks with a vehicle, the number of axles on the vehicle does not generally determine whether you should stop. However, specific regulations and guidance may apply to commercial vehicles or in special situations, so it's always best to follow posted signs and signals.