This endpoint returns a JSON array of the active Train Describer areas. This is the same as those returned by the root TD endpoint but is useful if you only want just the areas and not the rest of the information.

You will need these codes when querying each describer.

$ curl -s http://api.area51.onl/rail/1/td/areas
["A2","A3","AD","AL","AN",
    ...
    "YK","YO","ZA","ZB","ZE","ZG","ZH","ZR","ZY"
  ]