should vehicle state 'unknown' be included in the PROW

[jean-populus]

Is your feature request related to a problem? Please describe.

Currently the vehicle state unknown is considered 'Maybe PROW' in MDS (see State Machine Diagram). This has caused confusion among cities and providers as to when and why to include 'unknown' in PROW counts.

Note: how to use and implement vehicle state unknown by providers will be addressed in a separate issue.

Describe the solution you'd like

Provide guidance as to how to think about vehicle state unknown with regards to PROW counts based on MDS data.

Is this a breaking change

Imagining this would mostly be updates to descriptions but could change how the spec is being implemented depending on the outcome of the conversation.

• I'm not sure

Impacted Spec

This will affect all of them.

• agency
• policy
• provider

Describe alternatives you've considered

Leave things as is?

Additional context

Discussion Point A - unknown is NOT PROW

It really can't be overstated how natural "sum up the PROW states to count PROW" is. If we can standardize how long can a vehicle go without an event before moving to unknown via missing", and we then decide that we have enough standardization, so we stop counting unknown as PROW.

You might worry that providers would abuse this ability to move things to unknown if that is all it takes to remove things from PROW. But cities can still track unknown for other purposes, for example cities could use "% of fleet in unknown state" as a measure of operational quality.

Note: more context in #749 (comment)

Discussion Point B - lost_comms vs missing

I've seen instances where vehicles have a lot of transitions into and out of unknown on relatively short time scales via the comms event types and I would think those should continue to count as in the PROW. Whether a vehicle state is considered in or out of the PROW matters a lot for something like determining how long a vehicle has been parked in one place, which is a common regulation we help enforce at Populus. A vehicle that enters unknown on lost_comms and then goes back to available on comms_restored some time later in the same place has clearly not moved and we would consider that a continuous in-PROW parking event. But an unknown/missing transition would terminate the parking event under this model where it's used to communicate that a vehicle is permanently lost.

Note: more context in #749 (comment)

Discussion Point C - split unknown into missing and out-of-communication states?

For MDS 2.0 we could "split" unknown into missing and out_of_communication (or some such thing) if we want to make the distinction clear at the state level rather than the state/transition level.

Note: more context in #749 (comment)

[jean-populus]

folding this issue into the discussion #749