Motor vehicle crashes are well publicized in the US, where they kill over 40 000 people each year. It is less well known that motor vehicles can also be lethal while standing still. In most such cases, the motor vehicle may be a convenient way to commit suicide. In other cases the death is wholly unintended. Modification of motor vehicles may help prevent some of these deaths.

The best known measure taken to date to address risks from motor vehicle exhaust was intended to reduce chronic exposure to air pollutants rather than acute poisonings. The US introduced catalytic converters in 1975 to improve ambient air quality by reducing the amount of carbon monoxide (CO) and other pollutants emitted by the average automobile. This change apparently also reduced deaths from acute motor vehicle carbon monoxide (MVCO) poisoning, both intentional and unintentional.¹

Catalytic converters, however, do not remove all CO from exhaust. Motor vehicles emit toxic levels of CO when their emission controls malfunction or after cold starts,² and the engine can be “fooled” into putting out more CO when the vehicle is running in a tightly enclosed space.³ Emission controls therefore have not eliminated the MVCO poisoning problem, even though essentially all American cars now have them. In 1998, the most recent year for which deaths traceable to MVCO are available in the US,⁴ the …