Exhaust system Law in the United States and other countries to not have a catalytic converter. Converters may not be removed from a vehicle that is used only for "off-road" driving in the United States. The main purpose of a catalytic converter on an automobile is to reduce harmful emissions of hydrocarbons, carbon monoxide and nitrogen oxides into the atmosphere. They work by transforming the polluted exhaust components into water and carbon dioxide. Cat-back (also cat back and catback) refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. This
Alternatives to car use (petroleum-powered) car and contribute to transport sustainability. They also provide other significant benefits such as reduced traffic-related injuries and fatalities, reduced space requirements, both for parking and driving, reduced resource usage and pollution related to both production and driving, increased social inclusion, increased economic and social equity, and more livable streets and cities. Some alternative modes of transportation, especially cycling, also provide regular, low-impact exercise, tailored to the needs of human bodies. Public transport is also linked to increased exercise, because they are combined in a multi-modal transport chain that includes walking or cycling. According to the MIT Future Car