Update E022 - Split out same times from decreasing times

[isabelle-dr]

Issue by barbeau
Feb 12, 2020
Originally opened as CUTR-at-USF#365

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Summary:

E022 rule currently flags two cases:

Prediction time is the same across stops
Prediction time decreases across stops
After talking to a few agencies, it looks like the first can occur in systems that don't have a high precision of scheduled arrival/departure times in static GTFS stop_times.txt. So, if they have the same scheduled times across several stops, and the RT system is schedule deviation-based, it will also predict the same RT arrival/departure times across stops. So agencies may want to ignore this in certain cases (although ideally the system would provide better predictions).

The second case is always an RT error - the bus should never travel backwards in time when moving between stops.

So, we should split out these two cases into different rules.

Question - do we downgrade the first case to a warning? Maybe we make E022 specific to traveling backwards in time, and add a warning for the first case?

Also, let's rename the rule to make it easier to understand (e.g., predictions vs stop_time_update).