Impact of vehicles with idle engines may be negligible

Under the Environmental Protection and Management (Vehicular Emissions) Regulations, the engines of parked vehicles must not be left idling. This is to reduce air pollution, for better public health. (“NEA clamps down on drivers who leave engines idling”; Nov 21)

The rule seems misplaced, though, without an in-depth comparison of the percentage of parked vehicles with running engines and that of other vehicles on the road, whether they are moving, stopping at traffic lights or being caught in traffic jams, at any one time.

The percentage of the former may be comparatively insignificant that the environmental impact may be deemed negligible.

Unless many vehicles with idling engines are parked at the same time in an enclosed area with limited ventilation, such as a basement car park, any adverse effect on air quality, especially when these vehicles are in the open, may be minimal.