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Limitations of the road transport indicator

‘Vehicle kilometres travelled’ is a widely used international proxy for the pressures of road transport on the environment and human health. By understanding the total distance travelled on New Zealand roads, the types of vehicles we use, their age and fuel type, and how intensively we are using our road transport, we can learn more about the scale and type of pressure road transport is placing on the environment.

However, there are limitations to the use of the VKT proxy. It does not reflect improvements in engine efficiency over time, which reduce greenhouse gas emissions per kilometre travelled, nor improvements in engine technology, which reduce air pollutants harmful to human health.

The ‘vehicle kilometres travelled’ indicator only accounts for kilometres travelled by road vehicles. It excludes rail, sea or air transport modes, which also have effects on the environment.

Transport emissions are only one of a number of factors that contribute to adverse air quality. Industry and household heating can also be significant sources of harmful air pollutants. This indicator does not provide a direct measure of the effect of transport emissions on air quality and human health at the national scale. However, it does provide an indication of the pressure on human health from road transport and how this is changing over time.

Traffic congestion is not accounted for – during peak periods, more fuel is consumed and more emissions are generated per kilometre travelled than during off-peak periods. Nor does the indicator take into account improvements over time in fuel quality or exhaust emissions control technology.

There are a number of other environmental effects of road transport that are not discussed in this report card (eg, contamination of storm water from road run-off, vehicle noise, the effects of road construction and the disposal of vehicle wastes, including scrapped vehicles).

Since 2001, the vehicle kilometres travelled on New Zealand roads have been estimated from odometer readings, taken from all vehicles during Warrant and Certificate of Fitness tests. Compared to earlier estimation techniques, this provides a more accurate record of the total distance travelled, by all vehicle types, within a given year. However, vehicle travel undertaken by unregistered vehicles is not included in reported VKT.

 

This information has come from the environmental report card on vehicle kilometres travelled by road.

 

Return to the vehicle kilometres travelled by road page

Last updated: March 2009