Every bridge strike starts with the same gap in knowledge: the driver did not know - or did not believe - how tall the vehicle was. The law’s answer has been on the statute book for decades: a height notice in the cab, where the driver cannot miss it. It is one of the simplest requirements in the Construction and Use Regulations, and one of the most commonly wrong in practice - missing, illegible, or displaying the height of a vehicle the truck used to be.
Regulation 10 of the Road Vehicles (Construction and Use) Regulations 1986 makes it an offence to drive, or cause or permit to be driven, a motor vehicle with an overall travelling height exceeding 3 metres unless a notice is displayed in the cab, positioned so the driver can easily read it, and meeting the regulation’s requirements. Two obligations hide in that sentence. The notice must exist and be legible to the driver from the driving seat. And - the less-known companion rule - no other letters or numbers may be displayed in the cab that could be understood as indicating a height associated with the vehicle or any trailer it draws, unless they form part of a compliant notice. The faded sticker from a previous body configuration showing 3.8m on a vehicle now running 4.2m is not just unhelpful; displaying it is itself an offence.
The content rules are exact. The notice must give the vehicle height expressed in feet and inches, or in both feet and inches and metres - imperial alone is sufficient, metric-only is not, a relic of the regulation’s age that surprises fleets with continental kit. The height shown must not be less than the overall travelling height: you may overstate, never understate. And for most vehicles the stated height in feet and inches must not exceed the actual travelling height by more than 150mm - so the margin is capped both ways: no understating at all, no overstating by more than 150mm. A notice rounded up to the next foot is fine; one reading 16’6” on a 14’ vehicle is non-compliant, as is one reading 13’3” on a 13’6” vehicle.
The notice is only as good as the measurement behind it. Overall travelling height is the vehicle as it actually travels: body, load-securing equipment, any fixed superstructure, and - critically for tractor units - the trailer it is coupled to. The measurement discipline that works: measure each rigid vehicle and each trailer when new to the fleet, when modified, and whenever anything is fitted to the roof - air deflectors, aerials, refrigeration units and beacons all move the number; record it on the vehicle’s file; and set the cab notice from the measured figure, not the brochure height. Tractor units pulling different trailers need the combination’s height managed per trailer, which is why trailer height marking at the front of the trailer and a matching cab notice habit matter in swap-trailer operations.
The regulation exists because of what happens when it fails. A bridge strike is not a minor knock: it is train services stopped, structural inspections, five-figure damage bills, Network Rail claims for delay minutes that routinely reach six figures, a prohibition for the vehicle, and an OCRS entry that follows the operator for three years. The cab notice is the last, cheapest line of defence - the number in front of the driver’s eyes at the moment they choose the route. It works only if it is true: a driver who learns the sticker lies stops trusting every sticker, and the control is gone.
The compliance routine fits on one line: measured height on file for every vehicle and trailer, a compliant notice in every cab, a rule that body or roof changes trigger re-measurement and re-noticing, and a walkaround habit of checking the notice is present and legible. Add the route-planning link - drivers briefed that the cab number, not memory, decides whether the low bridge on the diversion is passable - and the regulation does the job it was written for.
Swap-body and multi-trailer work is where cab height marking most often fails, because the number depends on the trailer, not the unit. The workable systems put the trailer’s measured height on a durable plate at the front of the trailer where the driver coupling up cannot miss it, and make checking it against the cab notice part of the coupling routine - as automatic as the suzies and the number plate. Where a combination would exceed what the cab notice says, the notice changes before the vehicle moves, not after the first bridge sign. It is a two-minute habit at the coupling point that protects the one number that decides whether the next low bridge is a route or a headline.