Which of the following is a requirement for testing modified or aftermarket vehicles?

The requirement for testing modified or aftermarket vehicles is that they must comply with emissions standards applicable at the time of manufacture. This ensures that even if a vehicle has been modified or had aftermarket parts added, it still meets the emissions regulations that were in place when it was originally manufactured.

This regulation is critical because it sets a baseline for acceptable emissions levels based on the technology and standards of that time. Modifications may affect how emissions are produced or controlled, but the fundamental requirement is that vehicles cannot exceed the emissions limits that were established when they were initially built. Thus, maintaining compliance with these original emissions standards is essential both for environmental protection and for ensuring that modified vehicles do not contribute to increased emissions beyond what was originally permissible.