Ian McLean Spokesperson for the Green Party

Wondering how to reduce both your carbon production and your transportation costs? Well, a bicycle as your second car is the best option, but if that is not possible…

The cost of fuel, and taxes on fuel, have both hit record highs recently. If you are considering changing your car, the following points might help.

One litre of diesel produces 14 per cent more carbon than one litre of petrol. However, diesel-powered vehicles travel about 30 per cent further on one litre than an equivalent petrol-powered vehicle. Diesel is therefore better for carbon production.

Diesel is better in relation to production of carbon monoxide, nitrous oxides and hydrocarbons, but worse for production of particulates. Fortunately, most of these emissions are removed from the exhaust of modern vehicles.

The cheaper apparent cost of diesel at the pump is an illusion. It turns out that minimising your spend on fuel depends on the fuel consumption of the vehicle. Small diesel vehicles cost more to run than small petrol vehicles – and the reverse is true for larger vehicles. On today's prices, the crossover (for example, when operating costs are identical) is at a fuel consumption of about 7.75 litres per 100 km (Figure 1).

Thus, if you need a larger vehicle, get diesel power. If small is okay, buy petrol. Of course, driving style, age and make of vehicle are relevant. But your driving style will be about the same for both fuels, so the advertised fuel consumption ratings should be a fair indication of relative operating costs.

Fully electric vehicles have arrived, but are not yet price-competitive. The fuel efficiency of hybrids is now competitive with small cars. But they do not yet support that great kiwi icon, the tow-bar. Overall, the best cost and environmental savings are still from using the car less. And by using that bike.

Figure 1. Operating costs for diesel and petrol vehicles in relation to fuel consumption / 100 km.

*Based on diesel tax of $53/1000 km, an on-line diesel licence purchase cost of $4.80 for 5000 km, petrol at $2.30/litre, and diesel at $1.60/litre.

Ian McLean is a spokesperson for the Green Party of Aotearoa New Zealand. He can be contacted on 021 547556 or 07 5794670, or email: ian.mclean@greens.org.nz