Under what conditions are Vehicle IDs generated?

[Kathryn DiPippo]

Hi developers! Hoping this might be a quick question; apologies if it's already been asked. Last week, I was testing using an Orange Line Subway train with ID 5454186D. Today, when I went to run the ID, it states the vehicle no longer exists. I'm currently using vehicle ID 54544CD9 on the Orange Line for testing. But how are IDs for trains re-generated? Does it refresh the train's ID whenever a new conductor takes over, or is the lack of train 5454186D indicate that the train was taken in for service testing? Thanks!

[Developer at MBTA]

Hello Kathryn,

First, a (somewhat-simplified) description of subway operations: An Orange Line train consists of six cars, which are formed into a "consist" at Wellington Yard before they are put into service. A car might need to be taken out of service for maintenance, but the other cars in the train might be re-formed into a different consist. So if you think of a "train" as being a particular set of cars, there's no guarantee that it will continue to exist for any particular length of time.

However, the way our software works is somewhat different from this idealized reality. Even though a train might keep the same set of cars from one day to the next, it will always get a new Train ID at 2:00 AM every morning when we re-assign all train IDs. A new ID might also be generated mid-day if the train went out of service at a yard and later came back into service.

I hope this answers your question. Let us know if you have any additional questions.

Sincerely,

Developer@MBTA

[Stefan Wuensch]

For what it's worth... Vehicle IDs differ from Trip IDs in that Vehicle IDs never change for a _certain_ car / coach / bus, while Trip (Train) IDs are what are regenerated every 2AM. A Vehicle ID is literally the ID number of the physical piece of equipment (painted on the side), which is assigned by the MBTA when it purchases that vehicle. That actual physical Vehicle ID is the "label" attribute in v3.

Any particular Vehicle ID will only be seen if that car/coach/bus is actually in service on a trip however. Additionally on Red/Blue/Orange Lines the Vehicle ID is from the leading (front) car, so for example a consist showing vehicle 1822 on the way to Alewife might show Vehicle ID 1866 on the way to Ashmont. (That's a real-world example of a consist on the Red Line I just watched change directions at Alewife.)

The Green Line is unique in that every car on a train is identified, with the leading car appearing first, as in:
"label": "3604-3814"

In case it helps, Vehicle IDs ("label" in v3) will **always** be in the following ranges for now (until we get the new cars):
Blue Line 0700-0793
Orange Line 1200-1319
Red Line 1500-1885
Green Line 3600-3894
Mattapan Line 3072-3271
Commuter Rail 1500-1827

The quasi-official source for that is http://www.transithistory.org/roster/ which is maintained by staff from MBTA & CTPS in their spare time. Note the actual Orange & Red IDs have a leading zero as in 01885 but in practice that leading zero is dropped.
(There's also bus numbering on that page, but it's too complicated for me to summarize here.)


-- Stefan