Impairment vs Risk vs What Should an Employer 'Reasonably' Know...? The short answer is yes and yes. Yes he knows its monitored and yes the consent is a part of the deal when Bob accepted the vehicle. — Rachael
So no issue that as a part of normal checks and balances his employer has become aware of the company wagon being out and about at odd/regular times during the night. Therefor an informal chat/heads up, along the lines of "hey Bob, some random checks of your company car have shown that it's out and about at odd times during the night, is that something we should be concerned about?" is a fair and reasonable question.
Without knowing whether there is a pattern of the same addresses night after night, or a variety of different addresses and times, you are guessing what the reason maybe, but the times are revealing a potential safety issue simply from the driving while fatigued perspective. And that is quite apart from any H&S issues arising from working while fatigued.
Once you have had the conversation with Bob, you will be able to add the "why" to "when, where and for how long", but so long as you don't prejudge the situation and establish the facts, you can proceed accordingly (and inline with your employment contracts/procedures).
In my egg round truck driver, I solved the problem by figuring out his route/time table, then i appeared at one of his drop off points just after he got out of the back of the truck with some trays of eggs. He was suitably shocked, didn't drop his eggs though.
As the truck was supplied to us under contract from it's owner, I just said, we'll hire the bare truck from here on in and find our own driver. We then told the drivers about the GPS system, and upgraded it so we could message them and they us- whole thing worked so much more smoothly after that.