Skip to main content

Motor vehicles

Motor vehicles can be a source of air pollution in the Waikato region. Vehicle emissions affect human health and the environment. Find out how to reduce petrol and diesel vehicle emissions while saving yourself money, improving engine efficiency and reducing engine wear.

On this page: Vehicle emissions, Vehicle emissions testing, Are petrol and diesel emissions different?, What you can do

Emissions from motor vehicles are generally not a major contributor to air pollution in the Waikato Region. But, in urban areas such as Hamilton, emissions from motor vehicles can produce large quantities of air pollution.

Vehicle emissions

Motor vehicles produce a range of contaminants that can pollute our region’s air, such as:

These contaminants affect the environment and human health. Find out how we monitor carbon monoxide, nitrogen dioxide and fine particles in the Waikato region.

Vehicles are also an important source of carbon dioxide, a greenhouse gas associated with climate change.

In Hamilton, air pollution from vehicles varies from suburb to suburb and is highest in central Hamilton. Vehicle emissions are highest when traffic density is greatest - between 10am and 4pm.

Vehicle emissions testing

In 1996 Environment Waikato and Hamilton City Council ran the Hamilton Motor Vehicle Exhaust Emissions Project. Between May and December 1996 they tested carbon monoxide and hydrocarbon emissions of 7,600 petrol vehicles.

As part of the Festival of the Environment, Environment Waikato tested the carbon monoxide and hydrocarbon emissions from 308 motor vehicles, in March 2002. Test results showed that one in five vehicles failed the test.

Carbon monoxide

Carbon monoxide was tested because it is a poisonous gas. It attaches to our red blood cells better than oxygen - reducing the blood’s ability to carry oxygen around the body. Low exposure to carbon monoxide causes in headaches, dizziness and nausea.

Graph showing the percentage of petrol vehicles passing emissions testing (1996).

Check out the carbon monoxide air indicator for information on how we monitor carbon monoxide and for tips on reducing the risks associated with carbon monoxide poisoning.


Hydrocarbon emissions were tested because they give a good indication of how efficiently a vehicle is running. High hydrocarbon readings indicate fuel wastage. Older cars and cars not well maintained tend to have higher hydrocarbon emissions.

The graph shows the percentage of vehicles that passed emissions tests for carbon monoxide and hydrocarbons in 1996. Newer cars had a progressively higher pass rate for both carbon monoxide and hydrocarbons.

Check out Waikato Regional Council's Passenger Transport Plan and Regional Land Transport Strategy.

Are petrol and diesel emissions different?

Petrol and diesel engines work in slightly different ways and burn different fuels, so they produce different exhausts. Compared with petrol engines, diesel engines produce smaller amounts of unburnt and partially burnt fuel (hydrocarbons and carbon monoxide) but can produce more nitrogen oxides and large amounts of smoke (fine particulates). These particles consist of soot, hydrocarbons, sulphur-based chemicals and volatile organic compounds (VOCs).

Heavy duty diesel vehicles, such as trucks, can be very polluting because they produce large amounts of particulates and nitrogen oxides. Diesel exhaust has also been shown to be a probable cause of cancer.

What you can do

You can help reduce the amount of air contaminants polluting our air by reducing the number of times you use a motor vehicle. You could try:

  • carpooling
  • using public transport (trains, buses and shuttles)
  • cycling
  • walking.

Check out the Bus Timetables for the Waikato region.

Find out how people living in the Waikato region travel to work.

If you do need to use a private motor vehicle to get around, make sure you drive smart and keep it in tune.

Drive smart - save fuel, protect the air

We all need to reduce the amount of air contaminants in order to reduce their damaging effects. If your engine is producing high levels of contaminants, it’s not burning fuel as well as it could. This costs you money and damages the environment.

The way you drive and how well you look after your engine can affect how much air pollution comes from your vehicle.

Save fuel when you drive:

  • Drive smoothly – accelerate slowly.
  • Travel light – don’t carry unnecessary loads.
  • Plan ahead – avoid short trips and unnecessary use of your vehicle.
  • Don’t overfill your fuel tank.
  • Don’t idle the engine unnecessarily.
  • Use air conditioning sparingly.
  • Ensure that the vehicle you buy is fuel-efficient.

Reduce smoke from diesel engines:

  • Use moderate accelerations rather than wide-open throttle accelerations.
  • If the engine starts to slow down, shift to a lower gear.
  • Back off the accelerator when climbing a hill or towing a heavy load. The extra fuel used with a wide-open throttle under load conditions is just making smoke, not power.

Keep in tune

Petrol vehicles

Maintain and tune your engine as recommended by the manufacturer. Many faults can increase contaminants in the exhaust, for example:

  • a rich idle mixture or incorrect air/fuel ratios
  • a dirty air filter
  • an incorrectly adjusted carburettor
  • defective spark plugs or worn distributor contacts
  • a faulty ignition coil
  • improper timing
  • vacuum leaks, burned valves, worn rings and head gasket leaks.

Diesel vehicles

Too much diesel exhaust smoke can indicate engine problems. Follow these tips to reduce smoke and keep your diesel vehicle well maintained:

  • Clean or change your air filter regularly.
  • Change your engine oil at least as often as the manufacturer’s recommendation. Dirty engine oil becomes thick. This causes excessive engine and turbocharger wear.
  • Maintain your engine’s fuel injection system (as recommended by the manufacturer). This includes changing the fuel filter at recommended intervals, regularly draining the water/fuel separator, having injectors checked, cleaned or replaced and the fuel injection pump maintained as needed.