A 150-tonne load crossing a bridge built for 44 is the calculation that keeps bridge engineers employed - and the reason abnormal-load movements carry a paperwork layer aimed squarely at structures. The bridge side of abnormal loads runs on indemnities, notices and checked routes; here is how the system actually works for the haulier.
Road wear and lane discipline are manageable; a bridge failure is not. So the STGO categories build the structures question into the notice system: Category 1 movements require two working days’ notice to highway and bridge authorities about the weight, with dimensions potentially going to the police; the heavier categories carry their own, longer indemnity periods - five days at Category 3 - during which the authorities can assess the structures on the route. The notice is not a formality: it is the window in which the bridge owners can say no, or say how.
The indemnity itself is the legal heart: by moving the load, the haulier indemnifies the bridge and highway authorities against the damage the movement might cause. That is why the authorities’ consent machinery matters so much - and why a movement made without the proper notice carries liability with no paperwork behind it.
The practical system is ESDAL: the haulier enters the load and the proposed route, and the system identifies every organisation that must be told - the police, the highway authorities, and the bridge and structure owners along the line. National Highways’ abnormal loads service exists to make the notification easier: the haulier plans the route, checks its suitability, and gets the full list of authorities to notify, with the system’s own mapping of the structures affected. Where a structure needs assessment beyond the routine, the process surfaces it - and the answer can be a condition, a diversion, or a no.
Three habits keep the structures side clean. Notify early, always within the category’s days: the two-day and five-day clocks are minimums, and the route with a doubtful bridge deserves more margin than the route without. Drive the notified route exactly: the indemnity and the assessments attach to the route on the notice - the diversion invented on the day is an unassessed structure with a 150-tonne experiment on it. And keep the records: the ESDAL record, the notices and the authorities’ responses are the file that answers the question if anything on the route is ever queried.
Bridges get their own abnormal-load regime for good reason: notice periods to bridge authorities, an indemnity from the haulier, and ESDAL to route the paperwork to every structure owner on the line. Notify early, run the notified route without improvisation, and keep the file - the structures side is where abnormal-load discipline is measured.
The authorities’ responses to a notification are not always clean yes or no: routes come back with conditions - a specific crossing speed, an axle-position requirement, a convoy-only arrangement, a route amendment around the structure that cannot take the load. The operator’s discipline is to treat the conditions as part of the authorisation, not as advice: the bridge that must be crossed at walking pace is crossed at walking pace, with the condition passed to the driver in the movement order and checked at the debrief. The conditional answer is the system working - it is how a 150-tonne load and a Victorian bridge reach terms. The operator who treats conditions as friction discovers the alternative: the authority that simply says no next time, or worse, the damage claim the indemnity makes payable by the haulier.
Bridges get notice, indemnity and assessment because they are the one part of the route that cannot be allowed to fail. Notify early, accept conditions as binding, run the notified route exactly, keep the file. The structures discipline is invisible when it works - which is precisely the point of it.
For the biggest movements, the notification is only the paper half - the route survey is the physical one: the crew or the surveyor driving the route first, measuring the pinch points, checking the structures, noting the street furniture that must come out and the overhead lines that decide the travel height. The survey feeds the notification with facts, and the authorities’ answers land on a route that has already been walked in daylight. Operators growing into heavier categories find the survey habit transfers downward usefully: even Category 1 and 2 work benefits from a driven route on new lanes, because the ESDAL map knows the structures but not the scaffolding that went up on Tuesday. Paper and tarmac must agree, and only the survey makes them.
The bridge regime is the abnormal-load world’s conscience: notice given, indemnity signed, structures assessed, conditions honoured, route driven exactly. It is paperwork that protects stone and steel - and the haulier’s balance sheet with them.