If you've ever opened a .ddd file in a plain text editor out of curiosity, you've seen a wall of unreadable binary characters. This article explains what's actually inside that file, in plain English, without needing to read the full EU technical specification yourself.
This is a companion, more technical piece to our main DDD file reader software guide — read that one first if you want practical software guidance rather than format internals.
What a .ddd file is, structurally
A .ddd file is a binary export defined under EU Regulation (EU) No 165/2014 and its related technical annexes. It is organized as a sequence of data blocks, each one covering a specific category of information rather than being one flat undifferentiated stream.
At a high level, a driver card .ddd file typically includes blocks covering:
- Card and driver identification data
- Driving activity records (driving, work, availability, rest/break periods)
- Events and faults recorded by the tachograph
- Vehicle usage records associated with the card
- Specific condition records (e.g. out-of-scope driving, ferry/train crossings)
A vehicle unit .ddd file covers a broader set of blocks, including overview data, activity data per day, events/faults, detailed speed data, and technical data about the unit itself.
What is a "TREP" in a tachograph download?
TREP stands for Transfer Request Parameter — essentially, a code that tells the tachograph unit or card which specific data block(s) to export during a download. Different download tools may request different combinations of TREPs depending on what data is needed.
This matters practically because two .ddd files from the same card can differ in size and content depending on which TREPs were requested during the download — a full download requesting all standard TREPs will produce a larger, more complete file than a partial one requesting only a subset.
Digital signatures: why you can't just edit a .ddd file
Every .ddd file includes cryptographic signature data alongside the activity records. This signature allows analysis software (and enforcement authorities) to verify that:
- The data originated from a genuine, EU-approved tachograph card or vehicle unit
- The data has not been altered since it was recorded
This is also why a .ddd file cannot be manually edited in a hex editor or similar tool without invalidating it — any modification breaks the signature chain, and compliant analysis software will flag the file as invalid rather than silently accepting altered data.
Generation 1 vs Generation 2 (smart tachograph) format differences
Both generations use the same overall .ddd container concept, but Gen 2 (smart tachograph) files include additional data not present in Gen 1 files, most notably:
- GNSS (satellite positioning) data at specific points during the shift
- Additional security/authentication data reflecting the stronger cryptography introduced for smart tachographs
- Vehicle Registration Number (VRN) capture tied to more specific vehicle-motion detection
Practically, this means Gen 2 files are generally larger and contain richer location context than Gen 1 files — but both are still standard .ddd files that compliant software (including TachoCard) should parse without the user needing to know which generation produced them.
Why you should never rely on file size alone to judge completeness
A common mistake is assuming "a bigger file means a more complete download" or vice versa. File size depends on:
- How much activity has accumulated since the last download (more days = more data = larger file)
- Which TREPs were requested (a partial download is smaller by design, not because of an error)
- Generation of tachograph (Gen 2 files tend to run larger due to additional data types)
The reliable way to confirm a download is complete is to check the analysis software's own confirmation (e.g. TachoCard confirming the expected date range was captured), not the raw file size.
Frequently asked questions
Can I open a .ddd file in Excel or Notepad?
No. It is a binary format, not a delimited text or spreadsheet format. Opening it in a text editor shows unreadable characters. Use dedicated tachograph analysis software instead — see our guide to opening a .ddd file.
What does TREP actually stand for?
Transfer Request Parameter — a code specifying which data block(s) should be included in a given download request.
Does a Gen 2 .ddd file work with software built for Gen 1?
Not necessarily. Software must explicitly support Gen 2 (smart tachograph) parsing, including the additional GNSS and security data blocks, to read Gen 2 files correctly.
Why can't I just edit my .ddd file to fix an error?
Every file carries a digital signature tied to its original, unmodified content. Any edit breaks that signature, and compliant software will treat the file as invalid rather than accept the change.
Related articles
- DDD file reader software guide
- How to open a .ddd file
- DDD vs V1B file differences
- TachoCard features
- Compare plans and pricing
Sources: EU Regulation (EU) No 165/2014; ETSI TS 101 573.
