Drivers’ hours law gets all the attention in fatigue management - the tachograph, the 4.5-hour rule, the weekly limits. But the Highway Code makes a quieter, more personal point in rule 91: driving when you are tired greatly increases your risk of collision, and the responsibility for that starts with the driver, before any legal limit is reached. A driver can be perfectly legal on hours and dangerously tired. Rule 91 is about the second half of that sentence.
The rule’s advice is a five-part discipline:
This is the point transport managers need to internalise and then teach. The tachograph enforces the outer legal boundary of driving time. It knows nothing about the driver’s afternoon off, their new baby, their second job, their cold, or the quality of last night’s sleep in the cab. Rule 91 operates in the gap between “legal” and “fit”, and it puts the judgment call on the driver - with the operator’s culture deciding whether the driver feels able to make it honestly.
A fleet where a driver who says “I didn’t sleep, I shouldn’t take the 4am trunk” gets thanked is a fleet where rule 91 works. A fleet where that driver gets grief gets drivers who drive tired and say nothing.
The rule’s advice, turned into fleet practice:
Sleep before the shift. “Get sufficient sleep before embarking on a long journey” is an instruction the driver owns, but the roster owns too: schedules that assume a driver can nap at any hour produce drivers who cannot.
Breaks as a plan, not a reaction. Fifteen minutes every two hours is easy to meet inside legal hours - it just has to be planned, not grabbed. Routes with known stopping points beat “stop when you feel it.”
The midnight-to-6am window. Night runs cannot always be avoided, but they can be treated as the higher-risk duty they are: tighter check-ins, better-planned breaks, and no hero culture around “pushing through”.
Sleepy means stop. The only effective treatment for sleepiness is sleep. A short nap at a safe, legal stopping place is a professional decision; pressing on is not toughness, it is impairment accumulating. And the safe place matters - the hard shoulder is not a rest area.
Fatigue sits at the junction of three regimes: drivers’ hours law, working time rules, and the general duty to be fit to drive that rule 91 expresses. The operator’s obligations run through all of them - realistic scheduling, honest tachograph discipline, and a reporting culture where fatigue is declared like a defect. The fleets that get this right treat a driver’s “I’m too tired” the same way they treat a driver’s “the brakes feel wrong”: stop, assess, fix. Nobody argues with the second sentence. The first deserves the same respect.
It is also worth being honest about what the rule cannot do. Rule 91 is advisory in form - there is no fixed penalty for starting a shift tired. Its enforcement happens after the fact: when a fatigue-related collision is investigated, the question “were you fit to drive?” gets asked of the driver, and the question “did your systems let an unfit driver drive?” gets asked of the operator. The rule is soft law with hard consequences.
Rule 91 is short: sleep first, avoid the small hours where you can, break every two hours, and stop when sleepy - somewhere safe. Every part of it is within a driver’s power, and every part of it is easier inside a fleet that plans for tired humans instead of ideal ones.