Train Question

I live right by the train tracks now. So I see a lot of trains each day. Like probably 20! More than enough. But today when I came home I saw something odd. The arms weren't down and the lights were flashing but I had to stop because there was this thing on the tracks. It looked almost like a street sweeper but it was going along the tracks. Does anyone know what that is? I wouldn't think it would really be something that cleans the tracks but I have no clue what it is... Any ideas?

Jessie