Final answer:
Passive regeneration of a diesel particulate filter usually occurs during normal driving without the need for driver intervention, utilizing high exhaust temperatures to oxidize particulate matter.
Step-by-step explanation:
The correct answer is that passive regeneration of a typical Diesel Particulate Filter (DPF) on a highway truck usually occurs during normal driving. This is a process that happens often without the necessity for the driver to intervene. Passive regeneration takes advantage of the high exhaust temperatures present during normal operation, especially on highways, to oxidize the particulate matter (soot) caught in the DPF without the need for additional fuel dosing or spark ignition. Alternative technologies such as plug-in electric vehicles and fuel cells are emerging as they offer zero tailpipe emissions, contributing to better air quality. Additionally, effective transportation planning can greatly reduce emissions and fuel usage for both passenger and freight transportation.