The Vietnam Automobile Transport Association has petitioned the Ministry of Construction to adjust the emission inspection process for diesel cars by removing the requirement that the accelerator pedal be pressed to the maximum during measurement.

Nguyen Van Quyen, Chair of the Vietnam Automobile Transport Association, said that he continues to receive many opinions from members and the scientific community. These opinions suggest that the regulation to "depress the accelerator pedal for its full travel" in a very short time (about 1 second) is not suitable for operational reality.

According to Quyen, diesel engines usually operate efficiently in the medium rpm range, approximately 1,600–2,800 rpm, while the maximum rpm can reach 3,500–5,500 rpm.

Sudden acceleration to maximum levels is rare in normal driving, making it an unreliable indicator of typical emissions.

Furthermore, according to manufacturer recommendations, every vehicle line has an optimal rpm threshold to ensure performance and durability. When exceeding this threshold, rpm may increase, but power does not increase correspondingly and may even decrease. On the dashboard, this area is usually warned with a red band, a zone where operation is discouraged.

The association cited the example of the Hyundai Santa Fe 2.2, which reaches peak power at around 3,800 rpm, while the danger zone begins at 4,500 rpm. Testing emissions at full throttle could pose risks to the engine, whereas testing at peak power levels would be both safer and more representative.

An inspection expert echoed this view, noting that the “full-throttle” requirement pushes testing conditions far beyond typical usage.

Diesel engines, he said, operate most steadily in the medium rpm range, which accounts for the majority of driving time. For a vehicle traveling about 100km per day, mostly at steady speeds, sudden full-throttle acceleration is highly unlikely, especially in urban environments.

“It is not reasonable to use an extreme condition to represent the entire operating cycle,” the expert said.

Peak emissions 

Another issue is that highest emission levels do not necessarily reflect typical emissions. Environmental impact depends on the cumulative emissions generated during regular operation, most of which occur under stable, everyday driving conditions.

As a result, testing vehicles only at maximum thresholds may be technically valid but fails to capture the full picture.

In several developed countries, emission testing methods have evolved. Instead of requiring throttle acceleration to measure smoke, authorities use diagnostic tools connected to the engine control system to collect real-time operating data.

Parameters such as engine speed, load, and operational history are recorded and analyzed, providing a more comprehensive assessment rather than relying on a single testing moment.

Practical pressures 

Regarding the fact that some inspection centers require vehicle owners to sign a commitment to take responsibility if the vehicle is damaged during the inspection process, the Vietnam Automobile Transport Association requested the abolition of this regulation.

The association said it is necessary to clarify the responsibility of the inspection unit in ensuring technical safety before checking emissions.

A representative of an inspection center stated that the requirement for a signed commitment stems from real risks, as the sudden acceleration action can cause technical incidents, easily leading to disputes if the car is damaged. Meanwhile, citizens have almost no other choice but to accept and sign to complete the procedure.

However, the representative argued that the above commitment does not have high legal value as it has not been prescribed in legal normative documents and is primarily internal in nature.

Another difficulty is that the inspection system does not have full data on the maximum rpm of each type of vehicle. The common parameter currently is the rpm at maximum power, while the actual maximum rpm is usually about 15–20 percent higher, making the inspection process somewhat dependent on the experience of the inspector.

“In many cases, determining the acceleration threshold is still a matter of estimation,” the expert said.

Facing the petitions, the expert argued that management agencies need to provide a response based on science soon. “Whether maintaining or adjusting, the policy needs to be clearly explained, based on data and practice. This is a technical field; decisions cannot be made based on emotion.”

Hoang Hiep