What’s the difference between a subway and a train?

While the most obvious difference between subways and trains is where they run, with one underground and one aboveground, there are other general differences. In truth, a subway could easily run as an aboveground train, as there's no needed functional difference.

the law, public safety, corrections, and security cluster prepares people for careers in planning, managing, and providing legal, public safety, protective services and homeland security, including professional and technical support services.

answer; rapid growth in buyer demand and high buyer switching cost;