Over the past two decades, substantial progress has been made in reducing emissions from new petrol engined road vehicles, with regulations setting limits on various emissions. In order to ensure that vehicles in-use are not producing excessive emissions, many countries employ an Inspection and Maintenance (I/M) programme that include a check on the exhaust emissions. This report reviews the various I/M programmes from a number of countries - both current and proposed. For conventional vehicles (i.e. without catalytic converters), the test generally includes an idle check with measurement on the level of carbon monoxide (CO limits 0.5% - 4.5%) and, in some cases, hydrocarbons (HC limits 100ppm - 1200ppm). For vehicles fitted with a three way catalyst, the test often involves an idle test and a fast idle test. Again the level of CO is checked (limits 0.10% - 0.50%), with an additional check on HC (limits 50ppm - 100ppm) or the air/fuel ratio (which must be close to stoichiometric) or both. The idle and fast idle tests provide a fairly cheap and simple means of checking the emissions, although the conditions are not representative of real driving conditions. A more representative test requires the use of a chassis dynamometer to apply load to the engine. Canada is currently (1992) setting up a programme that involves subjecting the vehicles to steady state engine speeds and loads, while measuring the emissions. In the USA, the Environmental Protection Agency (EPA) have proposed a new test programme that involves driving a vehicle over a transient driving cycle. (A)

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