The .TGD file is the specialized cryptographic container used primarily in Spain (and adopted by various European download keys) to store driver card data. While the rest of Europe predominantly uses the .DDD extension, the TGD format follows the same technical specifications defined in Annex 1B of Regulation (EC) No 1360/2002, but often includes specific wrappers for government-certified software.
Why the .TGD Extension Matters
For a transport company, the TGD file is more than just a document; it is a forensic record. Every time a driver inserts their card into a download terminal, the device extracts a binary stream of data. This stream is then digitally signed by the card's private key, creating a .TGD file that proves the driver's identity and activities without the possibility of external tampering.
Inside the .TGD: Data Structures
A standard TGD file is composed of several Elementary Files (EF) that store specific information blocks:
EF_Card_Certificate
Contains the Public Key Infrastructure (PKI) data used by authorities to verify that the file has not been altered since it left the card.
EF_Driver_Activity
The core of the file. It logs every change in activity (Driving, Rest, Availability, Work) with a resolution of 1 minute.
Technical Differences: TGD vs. DDD
| Technical Aspect | .TGD Standard | .DDD Standard |
|---|---|---|
| Data Origin | Driver Card (Personal) | Vehicle Unit (VU) |
| File Structure | Cryptographic Wrapper | Raw Binary ASN.1 |
| Typical Size | 15 KB - 40 KB | 30 KB - 100 KB |
Common Issues when Opening TGD Files
Since TGD is a specific format, many generic tachograph viewers fail to parse the information correctly, leading to common errors:
-
Signature Validation Failure: The most common error in Spanish TGD files. It occurs when the decryption tool doesn't recognize the certificate chain.
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Corrupted Data Stream: Usually caused by removing the card too early from the reader during the download process.
What the vehicle file knows that the card file does not
The two downloads are often treated as versions of the same thing. They are not. Each sees the operation from a different position, and the gap between them is where most findings come from.
- The card follows a person across every vehicle they touched.
- The vehicle unit follows a vehicle across every driver who used it.
Which means the vehicle file is the only place where certain things exist at all: movement recorded while no card was inserted, cards belonging to drivers you were not looking at, and the technical events — power interruptions, motion data conflicts, security breaches — that the card never sees.
Why it is the file that catches card swaps
A driver card can be moved between vehicles. The vehicle memory cannot. So when two records disagree about who was driving, the vehicle file is the independent witness — and on a smart unit it carries GNSS positions as well, which turns "who" into "who, and where".
The 90-day rule exists because the memory overwrites
The vehicle unit must be downloaded at most every 90 days, against 28 for the card. Two different clocks that never land on the same day, which is why the vehicle one is the one that slips.
And the reason it matters is not the fine. The memory is finite: once full it overwrites the oldest records permanently. There is no copy at the workshop, none at the manufacturer, none on a server. Download late enough and you are downloading a period the unit no longer holds.
That is the difference between defending yourself with data and defending yourself with words — and in a dispute, that difference is the whole case.
Legal Custody: 365 Days of Responsibility
According to EU laws, you must keep every .TGD file for at least one year. TachoTools provides a Legal Cloud Vault that automatically organizes your files by driver and date, ensuring you are always ready for a roadside inspection or a government audit.
Learn how we calculate per diems from TGD data →