Trucks are the principle means of moving goods within and between cities in most developing countries. They are therefore the workhorses of the economy. They are generally built to be durable and reliable and usually last for many years, even decades. Power and fuel efficiency are also considered important and valuable characteristics of trucks.

Because pollution control requirements on new trucks have lagged behind cars by many years, most existing in use trucks have very high emissions relative to cars. While stringent standards for new trucks are being phased in around the world, existing high polluting trucks will be around for many years unless steps are taken to address this problem.

One of the first steps that can be taken is to assure that existing trucks receive good maintenance and the principle strategy to do this is to implement an in use inspection and maintenance program (I/M). The inspection is used to identify trucks needing repair and the maintenance is carried out to do the repair.

Because the truck itself very often costs much more than the engine, another approach is to replace the existing engine with a new, more modern engine which meets more stringent pollution requirements. A common problem with this option is that the new engine needs more space which cannot be provided. The existing driveline (gearbox, rear axle, drive shafts, etc) of the vehicle must also be adjusted to the new engine. Alternatively, the existing vehicles can be retrofitted with one of a variety of pollution control devices.

Frequently replacing the old engine with a more modern one or retrofitting the old vehicle will also require a switch to a cleaner fuel. For example, if a catalyst will be used with a gasoline fueled vehicle, then lead free gasoline will be necessary. Similarly if a catalyst or particulate filter will be used with a diesel fuelled vehicle, careful attention to assuring the appropriate sulfur level in the fuel will be necessary. It is further important to prevent the use of adulterated fuels.

Finally a shift to a cleaner burning alternative fuel is possible although this step is taken less often with trucks than with buses because frequently, trucks will not have access to the fuel across the range of places that it tends to be driven. On the other hand a national shift to cleaner fuels will affect the whole population of vehicles resulting in a significant positive effect on the ambient air quality.

All of the approaches listed in this section have different characteristics in terms of energy efficiency, life cycle and tailpipe emissions. Most have the potential to reduce emissions from existing trucks but only if implemented carefully.