A DVSA examiner at a checkpoint near Immingham found a small electronic device wired into the speed sensor circuit of a Polish registered articulated lorry. The device, roughly the size of a cigarette packet, was designed to feed false speed pulses to the digital tachograph unit, making it appear the vehicle was stationary while it was actually moving at motorway speed. The driver had been running without any recorded driving time for at least nine hours. The device was hidden behind the dashboard trim. The driver was issued a prohibition notice, and the vehicle was immobilised at the roadside. The Traffic Commissioner's office confirmed in March that the operator's community licence authorisation had been withdrawn, though by that point the company had already ceased UK operations.

That Immingham case is fairly typical of what DVSA examiners are finding at major freight corridors, particularly around the Humber ports and Dover. According to DVSA's own compliance data for 2024, examiners issued around 4800 prohibitions for drivers' hours and tachograph offences across Great Britain, a figure that has held roughly steady for three years despite the rollout of smart tachograph requirements. What has changed is the devices themselves. Five years ago, the most common method was a magnet placed over the vehicle speed sensor on the gearbox, crude and easy to spot because the magnet is physically present during inspection. A compliance officer at a vehicle testing station in the East Midlands, who asked not to be named because he wasn't authorised to speak publicly, told me magnets now account for maybe a quarter of the manipulation devices they find, and the rest are electronic. Some need specialist diagnostic equipment to spot because they don't interfere with the tachograph's own test functions.

The electronic devices are often listed as "tachograph simulators" or "speed limiter testers". Arriving from manufacturers in China for between £300 and £800. The more basic type intercepts the signal between the vehicle speed sensor and the tachograph unit and substitutes a modified signal, typically either zero pulses to simulate a stationary vehicle or reduced pulses to understate speed and distance. The type that causes real headaches for enforcement is the CAN bus emulator, which feeds false data directly through the vehicle's data network and can affect the tachograph, the speedometer, and any telematics system relying on CAN bus speed data all at once. Sarah Thornton, a fleet compliance manager at a Leicester based haulier, told me she found one listed on a well known marketplace with installation instructions in six languages and a YouTube video showing how to wire it into a DAF XF in under thirty minutes. She reported the listing. It came down within a week, and three similar ones appeared in its place.

DVSA's ability to catch these devices at the roadside is constrained by numbers more than anything else. The agency employs around 300 traffic examiners covering all of Great Britain. Their job extends well beyond tachographs. A typical roadside check takes around 30 minutes. The examiner downloads the card and vehicle unit data and looks for inconsistencies, which can run considerably longer. In practice, examiners focus on the most obvious signs of manipulation, gaps in recorded activity, implausible rest patterns, and mismatches between odometer readings and tachograph distance data. An examiner might notice that a vehicle has apparently covered 400 miles with only two hours of recorded driving, but actually finding the physical device means pulling apart dashboard trim, and that isn't always feasible at a layby checkpoint with traffic moving past.

One problem that has been getting more attention over the past year is that CAN bus emulators don't just fool tachographs. A telematics specialist at GPSWOX mentioned they've seen cases where fleet managers assumed their tracking data confirmed drivers' hours compliance, not realising that the tracking platform was receiving the same falsified speed data as the tachograph because both were pulling from the same CAN bus feed. Independent GPS positioning will still show the vehicle moving even when the tachograph registers it as stationary, and that discrepancy is easy enough to notice if the fleet management software is set up to flag it automatically. Most platforms can do it. The alerts often sit alongside dozens of other notifications and don't always get looked at.

Penalties for tachograph fraud are theoretically severe. Drivers face unlimited fines under the Transport Act. Up to two years' imprisonment, and operators risk having their O licence curtailed, suspended, or revoked entirely. Traffic Commissioners dealt with 127 public inquiries involving drivers' hours offences in the 2023-2024 reporting year, resulting in 34 licence revocations and 52 curtailments, according to the Senior Traffic Commissioner's annual report. Mark Redmond, a transport solicitor at a firm in Birmingham, said the operators who actually lose their licences are almost always the ones caught with physical devices installed or where DVSA has downloaded tachograph data showing systematic patterns stretching over weeks or months. A driver running thirty minutes over on a single occasion almost never triggers regulatory action against the operator, and Redmond said that creates a perception among some smaller outfits that occasional corners can be cut without real consequences. He's had clients say as much to him in consultations.

The second generation smart tachograph became mandatory in the UK in all newly registered commercial vehicles from August 2023 and records vehicle location independently through GNSS, communicates with enforcement via dedicated short range communication, and has stronger security around the motion sensor. The tamper resistance is genuinely harder to defeat than anything in the older generation units. Retrofitting isn't required, though, and the UK's commercial fleet still includes hundreds of thousands of trucks running first generation digital tachographs or analogue units on vehicles old enough to predate the digital mandate entirely. Graham Telford, who runs a tachograph calibration centre near Warrington, estimated that perhaps 40 percent of the HGVs coming in for regular two year calibration still carry the older digital units. He's calibrated a handful of analogue tachographs in the past six months on vehicles from the early 2000s that are somehow still earning their keep. The device manufacturers will catch up with the smart tachograph eventually, he said, because the financial incentive for drivers trying to run extra hours hasn't gone anywhere.

DVSA's 2024-2025 business plan talks about earned recognition schemes and risk based targeting, using data from previous encounters to concentrate enforcement on operators most likely to offend. Whether that translates into more examiners at the roadside at the hours and locations where manipulation is actually happening is something the agency hasn't answered directly, and the staffing numbers suggest probably not yet.