jeffonabike

Their fee structure is a base rate plus a fixed rate per mile. From what I remember, those rates are determined by the typical demographic info + driving record/past claims. There are other companies that I believe try to adjust their rate based on driver behavior data, but metromile doesn't (at this time).

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.