Heavy Haulage

Adherence to bridge restrictions the key to maintain access

By Jonathan Bhana-Thomson, CEO, Heavy Haulage Association (July 2023).

Unlike 50MAX and HPMV permits for freight, the Overweight Permits issued for transporting large indivisible loads such as excavators and dump trucks, can have travel restrictions on specific bridges to ensure that they are not overloaded.

Overweight permits can also be issued to a range of other vehicles that are in their design heavier on the axle loadings than would otherwise be permitted – these include mobile cranes, drilling rigs, or agricultural vehicles to name a few.

It is key for the bridge structures to be conserved, and operate within the limits placed on them by the road owners, as this way the bridge is not degraded over time, and so become unusable while it is either repaired or upgraded.

There have been unverified reports that bridges have been closed following the movement across the bridge of either an overloaded general freight vehicle, or the non-compliance with bridge restrictions by an overweight load/vehicle.

There are a range of different restrictions that NZTA and local councils place on permits, but the regular ones are as follows:

Own Lane: this is where the load and transporters can stay in their own lane – but often there will be a speed designation provided – such as 20 or 50 km/h, which is the max speed permitted while crossing the bridge or structure.

Central: the transporter travels down the centre of the bridge, while maintaining the designated slow speed.

Offset: this is where the load/vehicle has to travel a designated distance from the kerb of the bridge. This is often where one side of the bridge has more capacity (and is often newer) than theother side of the bridge. It is important to check which direction that you are travelling and the offset is to which side of the bridge.

There is also the Do Not Cross designation. Obviously, this is where the axle loadings or gross weight is higher than the capacity of the bridge has been assessed to be, and you are unable to cross the bridge. In this case the load weight needs to be lightened or an alternative route found.

The method used to identify the bridge and its location is important for the person who holds the overweight permit to understand, and for the driver to be competent in. This system is known as Bridge Engineering Self Supervision, or BESS for short.

It is a requirement for all holders of an overweight permit to have BESS registered drivers if you have restricted bridges on your permit – or to use an external bridge supervisor (which are few and far between these days).

This BESS registration is issued by the NZTA and it has recently brought back the  administration of this in-house after using an external contractor for a number of years. The reports we’ve had is that this new admin system is working well.

Holders of BESS need to initially gain Unit Standard 23436 with a MITO-registered assessor, and then every five years to renew this, to ensure that the drivers have maintained their knowledge. This renewal material is currently undergoing a review between NZHHA and NZTA to bring it up to date and to get it in a new format.

The other key aspect that holders of overweight permits need to be conscious of, is the traffic control of other road users while the overweight vehicle/load is crossing a bridge. When the load is crossing the bridge in a crawl or other restriction that will impact on other road users, then there needs to be a load pilot provided to warn and control the traffic.

Generally in this situation traffic will need to be stopped ahead of the bridge, and for following traffic trucks need to be kept back at least 30m behind the overweight load – light vehicles can be closer.

These high level aspects of transporting overweight loads are key for those in the sector to understand and become compliant with. While there are a number of new bridges constructed on the roading network around NZ each year, we also need to maintain access to those existing structures that are older and are on key freight routes.

If you are not sure – ask for advice.


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