By Patrick McGuire
Chief executive
Cement & Concrete Association of New Zealand
The New Zealand concrete industry has long promoted the low maintenance, long-life and reduced fuel consumption benefits associated with constructing concrete road pavements. Yet, time and time again, decision makers have specified flexible pavements as a result of an apparent short-term strategy to minimise initial cost.
The Land Transport Management Amendment Bill, along with numerous other government and Crown entity sustainability initiatives, has placed an immediate emphasis on developing strategies to reduce carbon emissions associated with New Zealand’s roading network. Underlined by the escalating price of bitumen, current circumstances mean the need to seriously consider concrete pavements is now more pressing than ever before.
Sustainable transport
There has been much recent debate about the discussion paper “Sustainable Transport: Update of the New Zealand Transport Strategy” (UNZTS). Concern has been expressed that although the paper begins by reaffirming the Government priority of halving the country’s per capita greenhouse gas transport emissions, the majority of subsequent targets focus on the use of New Zealand’s roading network, not how the network is built or maintained.
Roading New Zealand has been quick to point out that the way roads are built and maintained will have a profound impact on reducing future carbon emissions, to the extent that it predicts Transit New Zealand and local authorities will eventually specify not only their technical and functional requirements, but also the maximum level of associated carbon emissions.
There is no doubt that Roading New Zealand’s observation is correct. However, it is not correct to suggest that the carbon profile of agencies that build concrete pavements is considerably greater than those who build asphalt pavements.
The embodied carbon dioxide (ECO2) of a tonne of concrete varies with mix design and is in the range of 75-176kg CO2/tonne. However, in terms of concrete pavements, long-term user and maintenance benefits, as well as numerous design options, combine to offset this figure.
Low future maintenance is one of the principal advantages of concrete pavements. There are examples of well-designed and constructed concrete pavements that have required little or no maintenance well beyond their 40-year design lives – the positive economic implications of which cannot be over emphasised. In addition to requiring less resource, reduced maintenance translates to reduced traffic congestion, and, in turn, fewer CO2 emissions from idling vehicles.
In heavily trafficked areas, the rigidity of a concrete pavement minimises the energy consumed in deflecting the pavement surface. This reduction in rolling resistance means less fuel consumption and corresponding CO2 emissions.
The use of concrete greatly reduces pavement depth compared with asphalt, which also means less non-renewable resources are consumed.
Evaluation practices
In order to accurately gauge the long-term user and maintenance benefits of the various alternative pavement types available, current evaluation practices need to be revised.
New Zealand evaluates paving alternatives primarily using LTNZ’s Economic Evaluation Manual (EEM1), along with the Land Transport Management Act and Strategy, and congestion and environmental considerations.
The following two factors are extremely influential in the decision making process:
- Twenty-five-year analysis period. New Zealand evaluates roading projects using a 25-year analysis period.
- Ten percent discount factor. An integral part of the EEM1 is the discounting of both costs and benefits using a 10 percent discount factor.
CCANZ believes that while the economic evaluation procedure used is very comprehensive, the two factors outlined above distort the decision making process, and may mean that the best option is not being adopted.
Although not specifically intended, the 25-year analysis period means that a pavement is evaluated for a life of about 25 years only. However, the initial cost of the road would only be marginally greater if it were designed for 40 years.
The 25-year design period is a legacy from New Zealand’s past, when a philosophy was adopted that advocated getting as much roading work completed with the available funds. It is time to rethink the fundamentals of the 25-year analysis period, as it may be short changing future generations.
A 10 percent discount rate is high compared to with those used by road authorities in other developed countries. Typically values of between four and seven percent are used. The consequence of using too high a discount rate is to focus on short-term rather than long-term costs.
On July 1, 2008, the New Zealand Transport Agency (NZTA) will be established as a Crown entity, and will replace Land Transport New Zealand and Transit New Zealand. The new agency’s mandate is to give effect to the Government’s vision for an affordable, integrated, safe, responsive and sustainable transport system by 2010. To show real commitment to meeting these objectives, the issue of concrete road pavements must be high on its agenda.
Contractor Vol.32 No.5 June 2008
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