Tim Davin: Inadequate analysis of effects of heavier trucking loads

Tim Davin examines the potential costs of allowing bigger trucks on our roads. Photo / Supplied

Who will bear the cost of heavier vehicles? Where will the costs of heavier vehicles fall, and will they improve New Zealand's productivity?

We really don't know the answers to these questions as the analysis has not been done.

The Ministry of Transport is proposing to increase allowable vehicle weights and dimensions, and this is principally being driven by the contribution this will make to lifting productivity. The argument is that this will enable freight transport to be more efficient, with more freight being able to be moved more safely and with less fuel, lower labour costs and less emissions. These are powerful arguments.

However, there is considerable concern that the analysis of the costs to date has not been adequate - particularly relating to the impact on roads, and it cannot be argued that it will improve productivity without such an analysis.

Studies to date suggest that there will be a 16 per cent reduction in the number of trips and a 21 per cent reduction in fuel use. This could have a positive effect on New Zealand's gross domestic product of between $250 million and $500 million a year.

The proposal will allow heavier vehicles to operate more freely but they will be restricted to specific routes.

The proposal is to increase weight limits from 44 tonnes to 53 tonnes - an increase of 20 per cent. The damage to road pavements is generally regarded to follow the 4th power rule which means that if a load is doubled, the damage to the road pavement increases 16- fold.

While there is ongoing debate about whether the number is smaller or larger than the 4th power, if we assume it is the 4th power, and axle loads are increased by 20 per cent then the damage to a road by each truck will increase 102 per cent - that is double. This far outweighs the reduction in trips of 16 per cent.

To date there has been no analysis of the impact on roads. This proposed change will result in many more loads over 44 tonnes on many more roads than is currently the case.

There is also concern that rather than decreasing the number of trips by 16 per cent with improved competitiveness, road freight will become more attractive to operators, and we may see increased trips and emissions.

With larger vehicles on more roads, and an increase in trucks, it's possible we will face a double whammy - more damage on more roads.

Until research is undertaken on the likely extent of the damage and the costs analysed in economic terms and balanced against the benefits, it simply cannot be concluded that this will improve productivity.

The impact of making an uninformed decision could be considerable. Twice the wear on roads will not be noticed overnight.

Road pavements are designed to withstand a certain number of (equivalent) axles over time. The proposed change will significantly shorten the usual 20-30 year lifespan of pavements, but the cost will not be felt for some time.

Rising costs will not be solely met through heavy vehicle road-user charges. Currently freight vehicles contribute around 37 per cent of the Government's revenue and fuel excise 63 per cent. Local government pay half the cost of local roads so increased maintenance costs will inevitably fall on petrol users and ratepayers.

The proposal to allow these increased loads on specified routes may not be practical. Freight movement relies not only on the state highway network but, at every origin and destination, local roads.

With more freedom of movement for large trucks, will it be practical to specify such large number of routes? How will we carry out suitability assessments of the routes? And how can we ensure trucks will use them?

Eighty-eight per cent of roads in New Zealand are local roads and a third, unsealed. Many trucks, particularly tankers, which are not currently full, are able to increase their loads without modification.

This means there is a real possibility that low-strength and low-volume rural roads and bridges will have to cope with much heavier milk and wine tankers. Growth in the agricultural and horticulture sectors will only exacerbate the problems.

The issues are much more complex than simply considering economic benefits, reduction in emissions and improvements in safety.The cost of the impact on roads must be assessed. Who will benefit and who will pay has to be evaluated. If we analyse the issues we can address them.

We all support improving New Zealand's economic performance and productivity but without a serious analysis it is not possible to conclude that an increase in vehicle weights will contribute to that goal.

* Tim Davin is director of public policy at IPENZ (Engineers New Zealand).