Summary report, average speed is very low

We generated a summary report, which as average speed in the range of < 3 mph, Ideally this is not possible. How is engine hour calculated? is summary report is based on this engine hour?

It is based of engine hours if your device reports it.

At the database where can I find the engine-hour? in tc_positions.attributes field?

Yes.

If the device doesn't report engine hours, can the server be configured to calculate engine hours instead, like with Odometer/Distance?

Yes, that's what Traccar already does by default.

If engine hour is not available and i am taking a summary report for a month, how is average speed calculated? is it something like

Average speed = total distance ran / (24*30) KMPH ?

Yes, but in the future we will hide this value.

Thanks you Anton