In short: Remote tachograph download pulls driver card and vehicle unit data over the telematics unit's mobile connection, so operators stay inside the GB rules (driver cards every 28 days, vehicle units every 90) without plugging in a download key. It fails where the vehicle stands still in poor signal, which is usually the depot, and the same gap stops the far larger camera, inspection and EV data every returning vehicle carries.
Key Takeaways
- The tachograph file is the smallest thing on the truck — A vehicle unit download is a few megabytes at most, while a four-camera recorder can write more than 30 GB in a ten-hour shift.
- Downloads fail where vehicles stand still — Workshops, steel-clad sheds and the back rows of a rural yard are where remote downloads stall and vehicles drift towards the 90-day limit.
- Give the yard its own uplink — A private 5G network across the depot lets vehicles offload footage, checks and diagnostics in the hour they are parked, before the recorder overwrites anything.
In a nutshell
What is remote tachograph download and how does it work?
Remote tachograph download is the retrieval of tachograph data from a vehicle over a mobile data connection, instead of a transport clerk walking to the cab with a download key.
The vehicle unit in the dashboard records speed, distance and driver activity; the driver card records the same activity for the person, whichever vehicle they drive. Downloading the vehicle unit requires authentication with the operator's company card, which locks the data to that operator. In a remote setup the company card sits in a card reader or card server at the office, the telematics unit in the vehicle connects to the tachograph through its CAN or front interface, and the two authenticate each other across the mobile network before the download starts. The resulting .ddd files land in analysis software such as Tachomaster or the telematics provider's own portal, where infringements are flagged against the drivers' hours rules.
Most of the large telematics providers offer it, including Webfleet, Microlise, VDO (through its DLD units) and Stoneridge. For a fleet of 80 vehicles spread across three depots, it removes the monthly chore of chasing drivers and vehicles with a download key, which is why it has become common place practice among hauliers of almost any size.
What are the GB rules on downloading tachograph data?
Operators must download data from each driver card at least every 28 days and from each vehicle unit at least every 90 days, and keep the downloaded data for at least 12 months so that DVSA can inspect it.
Those intervals are maximums. Many operators download driver cards weekly so that infringements are caught while the driver still remembers the day in question, and so that a driver who leaves the business does not take four weeks of unanalysed data with them. A missed download is an offence in its own right, and a pattern of them feeds the operator's Operator Compliance Risk Score (OCRS), which DVSA uses to decide whose vehicles to stop at the roadside.
The population of tachographs is also growing. Since 1 July 2026, goods vehicles of 2,501 kg or more carrying goods for hire and reward on international journeys must have a smart tachograph 2 fitted, as DVSA's approved tachograph centre special notice 02-26 sets out. Vans operating only within the UK remain exempt, but a courier or removals firm with a handful of vans crossing to the EU now has tachograph data to download and retain for the first time, and remote download is the obvious way to do it for vehicles that rarely come back to the same place twice.
Why do remote tachograph downloads fail?
They fail when the mobile connection drops partway through the session or never forms at all, and in our experience that happens far more often in the depot than on the road.
A download is a sequence: the telematics unit wakes, the vehicle unit and the remote company card authenticate, the data transfers, and the file is confirmed at the server. Lose the connection at any step and the session is abandoned, to be retried later. On a motorway that retry succeeds within minutes. In a vehicle parked for the weekend in a steel-clad workshop, or in the back row of a yard in the Fens where the nearest mast is several miles away, it may not succeed until the vehicle next leaves site. Some telematics units also limit downloads to periods when the ignition is on, to protect the vehicle battery, which pushes the window towards the minutes when the truck is moving around the yard.
The vehicles most at risk are those that move least: spare tractors, shunters registered for road use, vehicles in the workshop for a fortnight awaiting parts, and seasonal fleet parked up between peaks. The analysis software will show them drifting past 60 days, then 80, and the transport manager ends up walking to the cab with a download key anyway. That is the fallback working as designed, but it is also a sign that the depot's coverage is doing less than the operator assumes.
What else does a vehicle need to upload when it comes back to the depot?
A great deal more than the tachograph file, and most of it is bigger by several orders of magnitude.
- Camera footage. Multi-camera recorders are now standard on urban HGVs, partly for insurance and partly because, since 28 October 2024, Transport for London's Direct Vision Standard has required HGVs over 12 tonnes rated below three stars to fit the Progressive Safe System, which includes a camera monitoring system. Most systems send short event clips over 4G and keep continuous footage on an SD card or hard drive in the cab.
- Walkaround checks. DVSA's guide to maintaining roadworthiness expects a daily walkaround check before a vehicle is used. Digital check apps capture photographs of defects, and those photographs upload from the yard at five in the morning, when the drivers are all doing the same thing at once.
- Electric vehicle data. Battery state of health, charging sessions and charger telemetry, plus manufacturer over-the-air software updates that are best applied while the vehicle is parked and plugged in.
- Driver handhelds and cab tablets. Proof-of-delivery photos and signatures that failed to send on the round, route files for the next day, and the operating system updates the device manager has been queuing all week.
This is the ordinary data of running a compliant, insured fleet in 2026, and the depot is the one place every vehicle reliably returns to.
How much data is that, and can public 4G carry it?
For the tachograph, yes, comfortably; for continuous camera footage, not at the scale of a whole fleet.
Take a four-camera recorder writing each channel at a modest 2 Mbit/s. That is 900 MB per camera per hour, or 3.6 GB an hour for the vehicle, and about 36 GB across a ten-hour shift. Over a depot 4G connection achieving a realistic 20 Mbit/s uplink, one vehicle's shift of footage takes around four hours to upload. A depot with 40 trucks returning between six and eight in the evening would need several days of uplink to clear one night's footage.
So fleets upload event clips and leave the rest in the cab, where it is overwritten on a loop of days or weeks depending on the storage fitted. When a claim or a complaint arrives a fortnight after the incident, from a cyclist, a third-party insurer or the police, the footage that would settle it may already be gone, and the event trigger that should have saved it was set for a harsh braking threshold the incident never crossed. The recorder captured the incident; the depot network never got the footage off the truck.
What does a depot network for vehicle data look like?
It is a private mobile network covering the yard, the workshop and the parking rows, with enough uplink capacity to offload vehicles in the time they are parked.
In practice we design it as (i) one or more private 5G radios on the building and on existing lighting columns, using an Ofcom Shared Access licence in the 3.8 to 4.2 GHz band, with the frame configuration tilted towards uplink because the traffic flows from the vehicles to the office, (ii) an in-cab gateway on each vehicle with a public SIM for the road and a private SIM for the depot, which the camera recorder, tablet and handhelds sit behind, and (iii) a small core on site or in the cloud that hands footage, check photos and diagnostics to the systems that already consume them. A single well-placed cell can deliver an uplink in the low hundreds of Mbit/s, shared across the vehicles in its footprint, which turns a four-hour upload into something closer to half an hour and makes on-demand retrieval of a specific hour of footage a routine task.
There are trade-offs. The telematics unit that performs the tachograph download usually has its own modem and SIM and will keep using the public network; the private network improves the depot's position for everything else and does little for that file directly, unless the telematics provider supports routing through the in-cab gateway. Depot Wi-Fi is the obvious alternative, and many camera recorders support Wi-Fi offload out of the box. For a compact yard where vehicles park within 50 metres of the building, a few outdoor access points may be enough, and we would say so. Wi-Fi struggles on the larger sites, where vehicles park 200 metres from the nearest wall, trailers block line of sight and every client associates and roams on its own terms, and that is where a cellular network planned for the yard earns its cost. The per-vehicle gateway adds a few hundred pounds of hardware per truck, which a fleet of 40 has to weigh against the cost of one lost liability dispute.
Where should a fleet operator start?
Start with the reports the business already has, because they show where the depot gap is before anyone commissions a survey.
Pull the tachograph analysis report for the last quarter and list every vehicle unit that went past 60 days before its download succeeded, then note where each of those vehicles was parked. Ask the camera provider how many footage retrieval requests in the last year failed because the footage had been overwritten or the vehicle was offline. Check which depots the walkaround app reports as slow to sync at the start of the morning shift. If the same depot appears on all three lists, that yard is the one to cover first, and a radio survey of that single site will tell you whether a handful of access points or a private 5G cell is the right answer for it.