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Comment by ilikeatari | Hacker News Reader

Great article! The gear ratio data would be useful to potentially derive more granular driver behavior model (acceleration) that is less mass dependent than accelerometer sensor. However, I do wonder if there is a way to determine the usage of the reverse gear itself. This data is currently not universally available via OBDII. The reverse gear data would be very useful since large amount of accidents are backing accidents.

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From the data provided, it seems likely that OBD is reporting any speed while reversing as 0, so you could probably guess that when the engine speed is changing slowly (while above idle), and OBD reports vehicle speed as 0, the car is reversing.

This may be true - but even if the sensor is reading zero vehicle speed and greater than idling engine speed, it's difficult to assume these are in fact reverse and aren't just "engine revving" moments. Looking into a time-series breakdown of each moment - seeing if the engine speed is 'changing slowly' as you mention - would be key in properly identifying Reversing vs. Revving.

This is why I specified engine revving slowly; engines which are disconnected from the drivetrain tend to rev up very quickly. In addition, cars with automatic transmissions are a majority of the US fleet, and spend very little time in neutral.

> engines which are disconnected from the drivetrain tend to rev up very quickly

So do engines which are in reverse and being controlled by drivers who are imminently about to have an accident :)

This might also be specific to the Metromile hardware (OBDII interpreter). I just checked on my vehicle with STN OBDII interpreter reversing is showing non zero value (I increased the reporting frequency to 1Hz).

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