What a single audit will not solve

Once the audit is finished and the claims are submitted, it is natural to think the subject is closed. Part of it genuinely is. Part of it is not, and the difference between those two parts determines whether ongoing monitoring is needed.

Errors that disappear for good

A wrong CO2 class in a road toll system is a registration error, not a calculation error. The vehicle is registered in class one although, by its first registration date and its emissions figures, it belongs in class three. Every month the system correctly calculates the charge on the basis of what is registered.

Once the vehicle is reclassified, the error disappears. Not shrinks — disappears. Next month's invoice will already be correct, and monitoring will add no value at all.

There are others of the same kind: a recurring error in the rate written into the contract, a systematic Incoterms assignment in the customs value, an un-updated discount clause in the carrier's system. They all share one property — the error is in the setting, not in the invoice. Correct the setting and the invoices correct themselves.

Errors that come back

The scope of the ETS surcharge is calculated for each voyage separately. A voyage within the European Economic Area — 100%. A voyage from the EEA to a third country — 50%. At berth — 100%. The error here is not in a setting but in how a particular voyage is assigned, so it can occur on any voyage, no matter how many earlier ones were correct.

Counting free time in wagon demurrage is the same. Weekends, public holidays, the moment the clock starts, a cause not on the consignee's side. Every arrival is a fresh calculation, and every one of them can be calculated wrongly.

Duplicates. The same leg on two invoices, the same voyage through two intermediaries, the same surcharge both in the main invoice and separately. A duplicate does not happen because of a wrong setting — it happens because two documents were produced independently.

Tariff dates. Tariffs change, new ones apply from a given day, and carriers' systems are not always updated on the same day. The error occurs precisely in the transition period, and transition periods come round every year.

Errors that do not exist yet

The third category is the hardest, because an audit cannot contain it in principle — what is audited is what has already happened.

A new truck. You have acquired a vehicle. In the road toll system it is assigned to CO2 class one by default. Reclassification does not happen by itself: it has to be initiated, and separately in each country. In practice it often is not done — not out of carelessness, but because it is not assigned to anyone in particular. The result: the new vehicle pays at class one until somebody notices.

A new country. The vehicle is registered in Germany and has started running in Austria. In Austria there is no registration, because one registration does not apply in other countries.

A change in the regulation. The thresholds for assigning CO2 classes were tightened on 1 July 2026 — not by a new act, but by the ordinary step along the emission reduction trajectory, because the reporting period runs from 1 July to 30 June. Some vehicles that had been in class three moved to class two. That was not an error — it was a lawful increase. But if nobody says so, the higher invoice looks like an error and absorbs time on a check in which there is nothing.

And the other way round: if the change should have reduced the charge and the invoice does not show it, that is an error — but it can only be spotted if you know the change happened.

The practical conclusion

After an audit, one simple step is worth taking: sort the discrepancies found into two columns — “setting corrected” and “may happen again”. The monthly average of the second column is the real value of ongoing monitoring. Not the total audit figure, which is usually larger because it also includes the one-off errors.

If the second column is smaller than the price of ongoing monitoring, monitoring is not needed. What is needed is a repeat audit every twelve months and an internal rule that every new vehicle and every new country is checked at the time of registration.

If it is larger — monitoring will pay for itself, and it will pay for itself by exactly the amount that column shows.