Every driver has an opinion about speed humps. Fewer people know that the hump itself is a regulated piece of highway engineering with statutory dimensions - and that a hump built outside those limits is not just uncomfortable but unlawful. For fleet operators, the regulations matter two ways: they tell you what a legal hump looks like when your vehicles are suffering over a suspect one, and they frame the conversation when your drivers or your vehicles come to harm on traffic calming.
The Highways (Road Humps) Regulations 1999 set the geometry. A road hump must have a minimum length of 900 millimetres measured parallel to the centre of the carriageway, from where one face meets the road surface to where the other face meets it. Its highest point must be not less than 25 millimetres and not more than 100 millimetres above an imaginary line connecting the carriageway surface on either side. And no vertical face of any material forming part of the hump may exceed 6 millimetres measured vertically.
That last rule is the one that distinguishes a hump from a trip hazard: the profile must be a smooth rise, not a step. A “hump” with a vertical face beyond 6mm is outside the regulations - as is anything taller than 100mm or shorter than 900mm in length. The regulations also cover consultation about road hump proposals, lighting of road humps, and the placing of traffic signs, so the full installation - warning signs, lighting, dimensions - is the regulated object, not just the tarmac bump.
Damage claims and near-misses. A vehicle damaged crossing a hump that exceeds the legal dimensions has a concrete grievance against the highway authority. Air-suspended trailers, low-loading plant carriers and tankers with low-hung equipment are the usual victims; a measured photograph of the hump profile against the 100mm and 6mm limits is the evidence that decides whether the conversation goes anywhere.
Load security. Even legal humps at speed are a load-security event. A 100mm rise taken at 30mph by a 26-tonner throws the load against its restraints and the vehicle against its suspension. The Highway Code’s traffic-calming rule - reduce speed on approach, maintain the reduced speed through the whole calmed stretch, do not overtake within it - is not comfort advice for a laden HGV; it is the difference between a restrained load and a shifted one.
Route planning. Traffic-calmed streets are increasingly designed to discourage through-freight, which is their point. Where regular routes cross calmed areas, the fleet’s interest is in the planning and consultation stage - the regulations require consultation about road hump proposals, and local hauliers are exactly the consultees who can explain what a hump does to a loaded tipper at walking pace versus a car at twenty.
Driving standards. Cushions, humps and speed tables reward smooth, slow, straight crossings. Drivers who straddle cushions to save the suspension but cross into opposing space, or who brake hard on the hump itself, convert a regulated piece of engineering into a hazard. Brief the technique: slow early, cross squarely, no braking on the bump, watch for cyclists who may swerve around the hump’s edge.
There is a distinction worth teaching drivers between the hump family members, because the technique differs. Full-width humps and speed tables must be crossed by the whole vehicle; speed cushions are built wide enough to straddle with a car’s track but usually not with an HGV’s - a truck’s axle width means at least one side rides over the cushion regardless. Drivers should stop attempting car-style straddling that puts wheels into the gutter or across the centre line: the cushion was designed with the truck’s width in mind, and the correct crossing is slow, straight and square over it.
For operators with vehicles based in residential delivery work, it is also worth recording recurring problem locations. A pattern of suspension or load-shift issues on one calmed route is route-planning data: an alternative street, a delivery-time change, or a measured approach to the highway authority if the profile looks non-compliant. The regulations give you the ruler; use it before the repair bills accumulate.
Road humps are not random obstacles; they are statutory objects with a 900mm minimum length, a 25-to-100mm height band and a 6mm cap on vertical faces, wrapped in consultation, lighting and signing duties. Know the numbers and you know when your vehicles face a legitimate inconvenience to drive over properly - and when they have met something the highway authority needs to explain.