I spent most of a summer working agency, picking up whatever shifts came in — sometimes four days, sometimes six, occasionally pulling a long one when a yard was short and the money was there. No single week felt unreasonable. Fifty-eight hours one week, forty-four the next, sixty-two during a rush job out of Immingham. Individually none of it looked alarming.
Then a driver trainer at one of the yards mentioned the 17-week reference period, and I went and did the maths on my notebook at break. I'd averaged well over 48 hours across the previous six weeks. Not massively, but enough that if I'd been checked against the WTD properly, there'd have been a conversation.
The problem isn't any single week. It's the average. And for agency drivers working irregular patterns, the average catches you when you're not paying attention to it.
The WTD for mobile workers — the basics
EU 561/2006 — the assimilated rules that govern your driving time and rest periods — is the set of rules most HGV drivers think about. But the Working Time Directive for mobile workers runs alongside it. It covers your working time in a broader sense: actual hours worked, not just drive time.
The key WTD limit for HGV drivers is 48 hours per week on average. I say 'on average' because that's the mechanism — it's not a hard weekly cap in the way that 56 hours is a hard cap on driving. You can work more than 48 hours in any given week. What you can't do is average more than 48 across the reference period.
The reference period under the Road Transport (Working Time) Regulations 2005 — which implement the WTD for mobile workers in GB — is 17 weeks. Not four weeks, not one month. Seventeen weeks.
What counts as 'working time' under the WTD
This is where a lot of drivers get confused, because WTD working time isn't identical to the time that shows up on your tachograph as drive or work mode.
Under the WTD for mobile workers, working time includes: all driving, loading and unloading, assisting passengers (for PSV work), cleaning and maintenance, time spent keeping to schedule, time when you can't freely dispose of your time. Basically: if your employer could require you to work during it, it's working time.
What doesn't count: availability time — periods where you're at the vehicle or available but not required to work and can freely rest. And periods of rest, obviously.
For most drivers the practical working time figure will be close to but not identical to the tachograph work+drive total. Waiting time is the grey area. If you're at a loading bay and the bay is backed up for two hours, but you're expected to stay and you have no real freedom to leave — that's working time. If you're given a four-hour window and told to come back, that might be availability. The distinction matters when your weekly total is close to the limit.
How the 17-week average calculates
The reference period rolls. It's not a fixed 17-week block from January to April. It moves continuously, and at any point in time, DVSA or an enforcement officer could ask: what was your average over the last 17 weeks?
So you take the total working hours over the most recent 17-week period and divide by 17. That average must not exceed 48. Simple arithmetic — but the rolling nature means a run of heavy weeks followed by lighter ones averages out differently depending on where in the cycle you are.
Here's where it catches agency drivers specifically. If you've had three months of consistent heavy work — say, an average of 55 hours per week — your rolling average builds up. Even if you suddenly drop to 40-hour weeks, it takes months of lighter work to bring the rolling average back below 48. You can't fix a high average by taking one week off.
A driver who works 60 hours for four consecutive weeks has accumulated 240 hours. To average 48 over 17 weeks, the total over the full period can be at most 816 hours. If the first four weeks already ate 240 of that, the remaining 13 weeks can only total 576 hours — an average of 44.3 hours per week. Any week above that in the remaining 13 makes the average creep up.
The opt-out — and why it doesn't mean what most drivers think
There is a WTD opt-out for non-mobile workers — a mechanism where individuals can agree in writing to exceed the 48-hour average. Employers use it widely for office and retail staff.
It does not apply to mobile workers. HGV drivers covered by the Road Transport (Working Time) Regulations cannot opt out of the 48-hour weekly average. Full stop. Any contract clause that claims to give a driver this opt-out for hours purposes is not effective under the mobile workers' legislation. You can be asked to work more than 48 hours in a given week — and the reference period averaging mechanism accommodates that — but you cannot sign away the overall 48-hour average cap.
I've seen agency driver contracts that contain opt-out clauses. I've sat in a canteen while a driver argued that he'd signed an opt-out and was therefore fine to average 55 hours for as long as the work kept coming. The contract clause doesn't override the regulation. That's not how it works.
Night work — the 10-hour absolute limit
Alongside the reference-period average, there's a separate WTD rule for night work that gets almost no attention. If you work nights — and the definition of 'night' for this purpose is the period between midnight and 4am — your working time is capped at 10 hours in any 24-hour period on those days.
That's not an average. It's an absolute limit. There's no reference period to average it out over. On a night shift that includes midnight to 4am, you cannot work more than 10 hours. A 12-hour overnight shift that runs from 8pm to 8am contains the midnight-to-4am window, so the 10-hour cap applies.
I covered the night work rules in more detail in the post on the 10-hour night work limit, but it's worth knowing both limits exist because they interact differently. The reference-period average can be managed over time. The night work cap cannot.
Who's responsible for tracking it
Operators are responsible for maintaining WTD records for their employed drivers. That should include working time records showing weekly hours and, where relevant, evidence of compliance with the 17-week average.
For agency drivers, it's more complicated. You might work for three different operators across a 17-week period. Each operator has records of the hours you worked for them. Nobody necessarily has the full picture across all three.
The agency itself — the employment business placing you — has some obligations around WTD compliance. But in practice, the responsibility for knowing your own average across all placements falls on you if no one operator or agency has the full picture. Which is an uncomfortable position to be in at a roadside check.
Record-keeping and what DVSA can ask for
WTD records need to be kept for two years. DVSA can request them at a roadside stop or during an operator investigation. If an operator can't produce WTD records showing the reference-period average for a driver, that's a compliance failure independent of whether the driver was actually within the limit or not.
The infringement-severity scheme for WTD breaches is separate from the EU 561 scheme. The fines are different, the process is different, and some enforcement officers treat them as entirely separate matters — which they are legally, even if they relate to the same working day.
Keeping track of your own working time average across placements is the only reliable way to know where you stand. A notebook works. A spreadsheet works. If you want something that does the maths automatically, ShiftOwt tracks your hours across shifts and shows where your 17-week average sits — £5.99/month for drivers, agency pricing on request.
The 48-hour average is not aspirational. It's the legal limit. Averaging 55 hours for long enough isn't a sign of being a hard worker — it's a WTD infringement waiting to be documented.