Who inspects vehicle inspection centres?

I recently sent my car for inspection at a Land Transport Authority (LTA) authorised inspection centre, as this is a requirement before road tax renewal.

The test conducted on exhaust smoke and noise emission was at idling speed without load on the engine. Is this the correct methodology for conducting this part of the inspection? Does the LTA carry out audits of the inspection centres to ensure that tests are carried out diligently?

As the National Environment Agency (NEA) and LTA use mandatory inspections as a primary tool to control illegal vehicle modifications and exhaust emission, ensuring that the tests performed at these authorised centres are thorough is essential.

There is a proliferation of vehicles, especially motorcycles, with very loud exhaust noise, and many are foreign registered. How would NEA manage these vehicles, since they are not required to undergo mandatory inspection?

Phang Fook Ghay