Train of solid autoracks operate frequently through Flagstaff. Unfortunately there is no easy way to tell where they are coming from or where they are going by just observing the train. Since autoracks are freely interchanged with other railroads you will see a variety of autoracks from all of the major railroad lines in the US and Canada.
Common loaded trains are VBIRSBD1, VCLOPHX1, VKCKPHX1, VKCKRIC1, VKCKSBD1, VRICCLO1, VSDGCLO1.
Common empty trains are VPHXELP4, VPHXSDG4, VRICELP4, VSBDELP4.
Extra trains operate occasionally and will use section number 3 instead of 1. Some extra trains split at Barstow, so the symbols could be VBLUBAR3 from Blue Island Yard in Chicago, VELPBAR3, or VIHBBAR3 from the Indiana Harbor Belt in Chicago. Other extra trains are built at either Kansas City VKCKPHX3 or Clovis VCLOPHX3 for Phoenix or VKCKRIC3 for Richmond.
BIR Birmingham, AL
CLO Clovis, NM
ELP El Paso, TX
KCK Argentine Yard in Kansas City, KS
PHX Phoenix, AZ
RIC Richmond, CA
SBD San Bernardino, CA
SDG San Diego, CA
The VPHXSDG4 is an odd one as it often passes the Flagstaff camera twice. If there is a A&C crew available to handle the train as it comes out of Phoenix, then it will turn west at Matthie (just a couple miles west of Wickenburg), go over the A&C to Cadiz, CA then be interchanged back to BNSF. If an A&C crew is not available and there aren't a lot of them, then the train will continue north to Ash Fork turn east and get on the Transcon at Williams Junction. You might think that it would then reverse direction and go west since the destination is southern California. However, the siding at Williams Junction isn't long enough to hold the train. The next CTC controlled siding to the east is Canyon Diablo. If you run the train that far, you might as well go the extra 25 miles and yard the train in Winslow and then have it reverse direction. It depends on how much time the crew out of Phoenix has left before dying on the law. What looks wasteful from the outside is really the best solution when you consider all of the options and potential problems. And you get to watch the same train go by twice. This is also the operating plan for the BPHXSBD4 and BPHXLAC4.