Buried in every fleet’s tachograph data is a category that should contain nothing and usually contains something: driving time recorded by the vehicle unit with no driver card inserted, or under a card that does not match the schedule. Unknown driver periods are the tachograph equivalent of an unsigned cheque - the vehicle moved, the rules applied, and nobody’s record carries it. The tachograph rules framework expects operators to download vehicle unit data every 90 days and driver card data every 28 days and analyse both, and reconciling those two data sets is precisely how unknown driving surfaces. What the operator does next is what examiners judge.
Most unknown driver periods have mundane origins. The driver who forgot their card at home and drove anyway - an offence for the driver and a record problem for the operator. The card left in the previous driver’s slot, so yesterday’s driver is recorded as driving today. The pool vehicle driven on a borrowed card, or on no card because “it was only a yard move”. The agency driver whose card history never reaches the operator’s system. And the genuine malfunction: a card reader fault that looks like cardless driving until the workshop confirms it. Each cause has a different fix, which is why the investigation matters - “unknown driver” is a symptom, not a finding.
The rarer, darker origin is deliberate: driving without a card to hide hours, or card-sharing between drivers. DVSA treats unexplained unknown driving as a potential fraud indicator, and the examiner’s working assumption hardens with every week the period goes uninvestigated. An operator who can show a documented investigation - even one that concludes “driver forgot card, debriefed, system tightened” - has evidence of management control. An operator whose data is full of uninvestigated gaps has evidence of the opposite.
The method is reconciliation. The vehicle unit says the truck moved at these times; the schedule says who had it; the card data says what they recorded. Unknown periods are where the three disagree. The practical routine: analysis software flags the cardless driving segments, a named person matches each against the allocation sheet and the drivers’ whereabouts, and the driver concerned confirms in writing what happened - drove without card, wrong card slot, or no knowledge. The outcome is documented: an explanation filed against the record, a debrief where the driver was at fault, a repair where the equipment was, and a disciplinary or supplier conversation where the pattern repeats.
The time element matters as much as the method. An investigation that happens within days of the download finds drivers who remember the day in question; one that happens quarterly finds shrugged shoulders. Fleets that download more frequently than the statutory maxima - weekly is common among well-run operators - keep their unknown-driver list short and their investigations easy, because the memory is fresh and the records align.
The card rules put the driver side plainly: drivers must use their own card, insert it before driving, place it in the correct slot - driver in slot 1, second driver in slot 2 on multi-manned work - and make their cards available for downloading by their employer. Driving without a valid card when one is required is an offence in its own right, which is why the “forgot my card” conversation is a conduct issue as well as a data problem. The operator’s standing instructions should cover the scenario explicitly: no card, no drive - and a spare-card or recovery procedure for the genuine mishaps, because the alternative is a driver stranded miles from base making the wrong choice under pressure.
The examiner’s question about unknown driver periods is never really about the data; it is about whether the operator manages it. A clean answer has three parts: the reconciliation is routine - every download checked, every gap logged; every gap has an explanation on file, however mundane; and the repeat patterns have consequences - the driver with three forgotten-card incidents has had a formal conversation, the vehicle with the faulty reader has a repair record. Operators who run that loop find their unknown-driving rate trends toward zero, which is the only trend the system accepts. The mileage nobody owns belongs to somebody - and the regulator expects you to know who, every time.
The best operators treat the unknown-driver report as a standing agenda item, reviewed every week alongside infringement data. When the same names, vehicles or routes keep appearing, the pattern points to a process fix - a card allocation procedure, a pool-vehicle booking sheet, a briefing for agency staff - rather than another round of individual debriefs.