In article ,
Recliner wrote:
Thanks. I wonder why they have head and tail lights?

Yes, I wondered that. Perhaps for the benefit of (rare) track workers?

Probably because the same equipment runs outside in other places. The
Dallas-Fort Worth system is elevated, and the one in Phoenix is mostly
elevated other than an underpass under a freight railway.

Here's the DFW one: https://www.dfwairport.com/skylink/

Video of a ride on the PHX one: https://www.youtube.com/watch?v=RVLIe0VWouQ