What type of vehicles primarily require the two-speed emissions test?

The two-speed emissions test is primarily designed for passenger cars. This test is a standardized method used to evaluate the exhaust emissions of light-duty vehicles, which include most passenger cars. During this test, vehicles are measured for their emissions output at two different speeds, typically one at idle and another at a higher speed, to ensure that they are operating within the acceptable limits set by environmental regulations.

Passenger cars are reliant on internal combustion engines, which produce emissions that need to be measured for compliance with air quality standards. The two-speed test specifically assesses the effectiveness of the vehicle's emission control systems while simulating real-world driving conditions. This method is less relevant for electric vehicles, as they do not produce tailpipe emissions, and while hybrid vehicles do have an internal combustion engine, the emissions testing procedures can vary and often include different tests. Heavy-duty trucks generally fall under different regulatory frameworks and testing procedures, focusing on their larger size and increased emissions potential. Hence, the focus on passenger cars for the two-speed emissions test makes sense given their significance in contributing to overall vehicular emissions.