Abnormal loads

What is an abnormal load?

Where the ordinary limits end, who has to be told, and what lands on your desk.

The thresholds

Indivisible, and past the ordinary limits.

Indivisible means it cannot be split without undue cost or risk of damage. Notice is owed once the vehicle is over the weight limit for its axle layout, which is 44 tonnes at most. A single axle over 10 tonnes, or 11.5 tonnes for a driving axle, brings it in too. Past 2.9 metres wide or 18.65 metres rigid length, it is owed too. A load that could be split gets no such allowance. In Auroute each notification is sorted by the rules it moves under, so the heavy ones are one filter away.

Who it concerns

Weight brings in the road and bridge authorities. Size brings in the police.

Over the weight limits, each highway authority on the route gets notice, and so does the owner of each bridge it crosses. The haulier also indemnifies them against damage. The police are told about wide and long loads, and the heaviest. Each of them gets the chance to check before the load moves.

In practice

Notice, check, reply, record.

The haulier gives notice with the details of the vehicle and the load. You check the route and your structures, and reply: no objection, a condition, or a request for another route or time. Both sides keep a record, because the same questions come up again later.

The check

Will the bridge take it?

Auroute builds each structure from the spans, supports and widths on your record of it. It builds the haulier's vehicle from its axle weights and spacings, and drives it across. It checks the weights, the height and the width against the structure's limits. On a simply supported span it works out bending moment and shear too. Each answer reads “within” or “exceeds”, never “pass”. The sums sit beside it, and your engineer makes the call.

The awkward part

Each decision is simple. The pile is not.

Notifications arrive in bursts, the notice periods are short, and any answer may be questioned months later. In Auroute they land in one place, each structure on the route is checked against the vehicle, and the decision is recorded as it is made.

An abnormal load is one that cannot be split without undue cost or risk of damage, and is too big or too heavy to carry on a vehicle within the ordinary limits. The law calls it an abnormal indivisible load. Some special vehicles, such as mobile cranes, move under the same rules. Moving one has to be notified in advance, and sometimes agreed.

A load that could be split is different. Over the limits it is simply overloaded or oversize, and notice does not change that.

The thresholds

Weight and size decide it. On weight, the line is the limit for the vehicle's axle layout. That limit is 44 tonnes at most, and lower for most layouts. So a load on a lorry well under 44 tonnes can still need notice. A single axle is limited to 10 tonnes, or 11.5 tonnes for a driving axle. On size, the lines are 2.9 metres wide and 18.65 metres rigid length. Cross any one and notice is owed. Which lines are crossed decides who is told, and how much notice they get.

Who is told, and why

Every public road has a highway authority. For most roads that is the council. For trunk roads it is National Highways, Transport Scotland or the Welsh Government. Every bridge has an owner too. Often it is the highway authority. Others belong to Network Rail, a canal body or a private owner. Each answers for its road or bridge being safe.

Over the weight limits, the haulier gives notice and an indemnity against damage to each highway authority on the route, and to the owner of each bridge it crosses. Notice gives them the chance to check before the load moves. Even with an indemnity, a struck or overloaded bridge is still theirs to close, inspect and repair. Wide and long loads go to the police as well, and so do the heaviest.

What that means in practice

  • The haulier gives notice before the movement, with the details of the vehicle and the load.
  • Authorities check the route and its structures, and reply inside the notice period.
  • The reply is no objection, a condition, or a request for another route or time.
  • Both sides keep a record. The same questions come up again later.

The awkward part

Volume. Each decision is usually simple. The pile is not. Notifications arrive in bursts, and the notice periods are short. Any answer may have to be explained months later. That is the part Auroute takes off a team. They land in one place. Each structure on the route is checked against the vehicle. The decision is recorded as it is made.

Answering notifications in-house?

See one answered on your own network, from the notice to the structure check to the decision.

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