The number of smoky vehicles on the streets is still high despite an upcoming tightening on emission standards for these diesel users.

In a statement on Wednesday, the National Environment Agency (NEA) revealed that there were 5,809 enforcement cases from January to September this year. This is slightly lower than the 6,381 enforcement cases for the whole of last year, but has already surpassed 2011's figure of 4,794 cases.

These vehicles were caught for having a emissions that exceeded 50 Hartridge Smoke Units (HSU), which determines the opacity of the smoke. Owners of these vehicles were fined up to $5,000,

"With the increase in the number of smoky vehicles on our roads, motorists are urged to maintain their vehicles properly and regularly," said NEA. Starting Jan 1 next year however, all diesel vehicles will need to achieve a smoke opacity test result of 40 HSU or lower in order to renew their road tax.

The NEA said it has been working closely with inspection centres to alert owners whose vehicles have shown borderline results during check-ups.

The agency added that a six month grace period will be introduced for such vehicles, to allow them time to adjust.