Your tachographs are spotless. Your drivers are still falling asleep.
Before I built software I ran a coffee shop, which means I have written rotas that looked perfectly reasonable on the wall on Monday and had visibly broken someone by Thursday. The rota was legal. Every shift within limits, every break accounted for. And I still watched a member of staff pour a flat white with the thousand-yard stare of someone whose body clock I had personally dismantled, because I had rolled her from closes straight into opens without ever writing down a single illegal hour.
Nobody gets hurt when a barista is exhausted. Coffee gets slightly worse. Swap the espresso machine for forty-four tonnes on the M6 and the same blind spot becomes a different kind of problem entirely.
Every transport manager knows the rules cold. Driving limits per day and per week, breaks after so many hours at the wheel, daily and weekly rest. The tachograph records it, the software checks it, the infringement report lands on Monday morning. Compliance is measurable, auditable and, most weeks, achieved.
And yet drivers still fall asleep. Fatigue keeps appearing in collision investigations involving vehicles whose tachographs were spotless. The HSE estimates fatigue is implicated in around 20 percent of accidents on major roads. The uncomfortable explanation is that the drivers' hours rules were never a fatigue model. They are a legal floor, and a pattern can sit comfortably above that floor while still grinding a human being down, exactly like my rota did.
What the rules cannot see
Drivers' hours regulations count time. They do not model biology. Specifically, they have nothing to say about:
Time of day. A shift finishing at 6pm and a shift finishing at 4am can be identical on paper. Physiologically they are different events. Work through the circadian low, roughly 2am to 6am, and alertness drops regardless of how much rest preceded it. The tacho does not know what 4am is.
Cumulative pattern. The rules check each day and each week largely in isolation. Fatigue accumulates across the pattern: the fifth early start in a row is not the same as the first, even though each one individually is legal. My barista's Thursday was built on Monday, Tuesday and Wednesday.
Rotation direction. A run of lates rolling into earlies compresses sleep opportunity in a way no single-day rule captures. This was precisely my mistake, and I made it while genuinely trying to be a good employer. The rota looked tidy. Tidy is not the same as humane.
Everything outside the vehicle. Loading, waiting at the RDC, the commute, the paperwork. The tacho measures driving. The body measures the whole day.
This is exactly why safety regulators in rail and aviation moved beyond hours-of-service rules decades ago and started using fatigue models: tools that score the pattern itself for the sleepiness and error risk it is likely to produce. The HSE is explicit that compliance with working time rules alone is insufficient to manage fatigue risk. Road transport is largely still running on the floor-is-the-ceiling approach.
The same tool works on your rotas
The Health and Safety Executive's Fatigue and Risk Index is the UK's established tool for this. It takes a shift pattern and returns the probability that someone working it will experience high sleepiness, and the relative risk of a fatigue-related error, accounting for start times, shift length, rest gaps and cumulative load.
It was built with transport and other 24-hour operations in mind. Very few operators outside rail use it, for one main reason: it lived in a 2006 Excel spreadsheet that expects shift-by-shift manual entry, and the HSE withdrew even that from its website in June 2021 because the Excel version it ran on could no longer be supported. The methodology is still the UK standard. The tool to run it officially does not exist any more. That is workable for assessing one proposed pattern in a consultancy report. It is not workable for a live depot with forty drivers and a rota that changes weekly. I would not have run it on my coffee shop rota either, and I am the sort of person who builds fatigue software for fun.
From infringement reports to foresight
The shift worth making is from lagging to leading. An infringement report tells you a rule was broken last week. A fatigue score tells you which duties on next week's plan are likely to produce a dangerously tired driver, before anyone climbs into a cab.
In practice that looks like: the planned rota goes in, every duty comes back scored, and the flagged ones show why. The 3am start after a late finish. The sixth consecutive day. The pattern that is legal all the way through and exhausting by Thursday. Fix it in planning, where it costs nothing, instead of on the road, where it costs everything.
RotaPulse runs the HSE Fatigue and Risk Index on a full rota in the browser. No spreadsheet wrangling, no consultancy engagement. The rota is the hazard. This makes the hazard visible while it is still just a plan on a wall, which is the only point at which it is cheap to fix.
Paste next week's rota into the free calculator and see which duties come back red.
Sources
- HSE, Human factors: fatigue. Includes the statements that fatigue is implicated in around 20 percent of accidents on major roads and that compliance with the Working Time Regulations alone is insufficient to manage fatigue risk.
- GOV.UK, Drivers' hours rules, the legal framework this post argues is a floor, not a fatigue model.
- HSE Research Report RR446, The development of a fatigue / risk index for shiftworkers (2006)
- ORR, Managing Rail Staff Fatigue, Appendix D, how the fatigue and risk indices should be interpreted, and their time-of-day divergence.
- TUC, Fatigue: a guide for health and safety representatives