From a purchasing perspective, these strategies can be employed in two main areas:
Replacing older equipment in their own fleet.
Rewarding or assisting contractors that have newer, low emissions equipment. Public bodies can include terms in contract solicitations establishing preferences for low emission vehicles and equipment to be used on their project. In these cases, the terms of a contract solicitation can help induce a construction contractor to replace older, heavily polluting vehicles.
Because of the lack of emission control regulations for off-road diesel construction equipment until 1996, diesel engines used in construction equipment are more polluting than those used for on-road applications. EPA regulations have dramatically improved the emissions of on- and off-road vehicles over the past 20 years. Recently-manufactured off-road diesel-fueled vehicles (compliant with Tier 4 standards) must now be far cleaner than the older vehicles (Tier 1) - 96 percent reductions in particulate matter and nitrogen oxides; 86 percent reductions in hydrocarbons; and 74 percent for carbon monoxide.
Despite these EPA standards and the availability of cleaner vehicles, many fleet operators continue using older, highly polluting diesel-fueled vehicles. A California study estimated that half of paving equipment will be in use after 24 years after purchase, and half of excavators will be in use after 17 years. Other have also emphasized the delayed replacement.