By Ron Brown
Director, Transport Specifications
Associates Representative, Power Crane Association of New Zealand
Recent research made it clearly evident that some long-standing information that has been used in the establishment of a road user charges regime affecting the mobile crane industry has been incorrect.
It has always been assumed that the impact of heavy mobile cranes on the road network has been detrimental and that crane operators should make a better-than-fair contribution to the national road funding by way of road user charges (RUC).
The study carried out showed that RUC were set using tyre footprint areas as the basis for determining the pavement wear, based on tyre technology from past years, and did not consider road-friendly suspensions and multi-steering mechanisms that actually reduce pavement wear.
The overweight policy manual recognises elements such as axle spacing and tyre sizes, and these values are indexed to provide a basis for approval of overweight permits. It is clear from this that the policy is aimed at reducing bridge and pavement damage and goes some way to reward vehicles that have been designed with this in mind.
Tyres and suspension designs commonly used on mobile cranes have for some years been manufactured in such a way as to facilitate optimum mechanical advantage, and create a crane that is mechanically durable, easy and economical to operate. These design enhancements have also contributed considerably to the road-friendliness of these vehicles, both in terms of pavement damage and manoeuvrability.
Tyre sizes, while introduced to adequately support the mass of the vehicle, have also increased in footprint areas that reduce pavement damage from point loading. For example, a crane tyre weight of six tonnes (12 tonne axle weight) produces a pavement loading factor of approximately one third of a front tyre of a legally loaded truck at three tonnes per tyre.
These cranes are typically designed with hydraulic suspensions that balance the mass of the vehicle evenly on axles and reduce dynamic impact loads on road surfaces.
Typical set-ups on steering engage more axles in the steering process at low speeds to reduce scuffing of tyres, while engaging fewer steerable axles at higher speeds to improve stability and safety.
The design of suspensions for cranes is some what simpler than conventional heavy vehicles because the crane weight in travel mode does not vary much, so the suspension can be designed closer to the individual requirements of the vehicle. Whereas vehicles that carry payloads vary in weight from the truck’s tare weight through to its fully loaded condition, requiring suspensions to function correctly across the full range of loading conditions.
When considering the crane mass as a whole, say at 60 tonnes, for example, the authorities would be correct to consider the crane mass when crossing bridges and be of the opinion that they have to protect these bridges; therefore the RUC should cover this expense.
The method of protecting bridges is to simply control the speed of the cranes, as they do currently with the permit system.
Distance travelled
Distance travelled by all-terrain cranes has a further influence on the relative level of pavement damage when compared to the total population of heavy vehicles.
Based on information from the Ministry of Environment, the distance travelled by the national fleet is reported as 40.2 billion kilometres for the year 2007. Of this, total, heavy vehicles, excluding buses but including all-terrain cranes, account for 6.9 percent of the total kilometres.
Crane estimates show that the total distance travelled by all-terrain cranes amounts to approximately 937,000 kilometres, which is 0.034 percent of the total distance travelled by heavy vehicles or 0.0023 percent of the national fleet.
Cranes, by design, only use the roads to travel to locations where they carry out the function for which they are designed, therefore do not travel on the roads unless they are travelling to a project.
What values are we talking about?
From an extensive set of tables for carrying out an assessment as to where the cranes should fit in regards to the RUC, there are two examples. One being the least RUC paid by trucks and cranes and the other being the maximum amount as detailed in the RUC manual.
Lowest values shown:
6x4 truck = $398.54 per 1000 km.
Three axle crane = $3400.91 per 1000 km.
Difference = $3001.37 per 1000 km.
Highest values shown:
6x4 Truck and two axle trailer = $950.70 per 1000 km.
Five axle crane = $6200.20 per 1000 km.
Difference = $5249.50 per 1000 km.
When these RUC charges are reflected in conjunction with pavement contact comparisons, the disparity between vehicle groups becomes obvious. It can be clearly seen from the data available that the other types of heavy vehicles create point loading as the direct result of their collective foot print areas and yet they attract a fraction of the RUC charges relative to the foot print pressure.
Even when considering that other heavy vehicles/combinations are said to travel for 50 percent of their distances in an unladen condition, the RUC charges for these vehicles are substantially lower than the all-terrain crane population.
Since the RUC are the equivalent of road taxation applied, and are directly connected to the cost of maintaining and expanding the roading infrastructure, it is reasonable to assume that the extent to which any vehicle is taxed through the RUC process should have a direct relationship to the extent to which that vehicle depletes the quality of the infrastructure.
From the information at hand, the logical conclusion is that all-terrain cranes contribute a highly disproportionate level of road tax through the RUC system and comparisons of these vehicles to other road user types should be re-evaluated with a view to re-grading the RUC platforms for all-terrain cranes.
Contractor Vol.34 No.8 September 2010
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