SINGAPORE - Owners of petrol vehicles will have to maintain their cars and bikes regularly if they are to pass regular inspections next year.

From April 1, 2018, most of these vehicles will have to emit less carbon monoxide than now, and will have to meet a new hydrocarbons cap.

For instance, any car registered between Jan 1, 2001 and March 31, 2014 currently cannot have more than 3.5 per cent of carbon monoxide in its emission. This cap will be lowered to 1 per cent from April next year. On top of that, the emission cannot contain more than 300 parts per million (ppm) of hydrocarbons, a byproduct of imperfect combustion.

For cars registered from April 1, 2014, the standards are even higher - a carbon monoxide composition of no more than 0.3 per cent, and a hydrocarbon make-up of no more than 200ppm at an engine speed of 2,000rpm. At idling speed, these cars should have no more than 0.5 per cent of carbon monoxide in their emissions.

Motorcycles registered between July 1, 2003 and Sept 30, 2014 will also have to meet a hydrocarbons cap - 7,800ppm and 2,000ppm for two-stroke and four-stroke models, respectively.

The hydrocarbons cap for those registered from Oct 1, 2014 will be even lower at 1,000ppm. On top of that, these newer models cannot have more than 3 per cent of carbon monoxide in their exhaust gases, down from 4.5 per cent now.

For diesel vehicles, the National Environment Agency (NEA) said the current smoke opacity test will continue to apply. The opacity test was last tightened in 2014, from 50 HSU (Hartridge Smoke Units) to 40 HSU.

Explaining the difference in test treatment, the NEA said petrol vehicles generally emit more carbon monoxide and hydrocarbons while diesel vehicles generally emit more smoke (a proxy for particulate matter).

"This is in accordance to international practices on testing of emissions from in-use vehicles," it added.

The Straits Times understands that existing vehicles will be able to meet the heightened inspection standards as long as they are well maintained with proper and regularly servicing.