Legislation is enacted to serve a purpose and is meaningless if not properly enforced. The idling engine ban is an example. When the law was introduced in 2011 after years of tussle with the various stakeholders, concerns were raised that the exemptions to the law were so numerous that the ban lacked bite. If experience over the past two years is any reference, our worst fears appear to have come true. Not only has enforcement been slack and minimal, roadside pollution has failed to show any significant improvement.

That the idling engine law itself is still idling on the statute book is regrettable. A recent visit by the to Beach Road in Repulse Bay confirmed just how slack enforcement was. Packed with tourist buses throughout the week, the beachfront thoroughfare is among the dozens of so-called black spots identified by the authorities. Our reporter found that at least half of the buses had their engines running for longer than the three minutes permitted by the law. Officially, only two penalty tickets were issued during the 11 patrols in the area between July and December. That means there were only two patrols per month on average. The figures sit oddly with the government's commitment to paying closer attention to the black spots identified.

The situation across the city is not reassuring either. While complaints about idling engines dropped by 40 per cent to about 1,000 cases last year, enforcement appears to take the form of gestures. Of the 3,184 drivers timed since the law came into effect, only 89 have been fined. With a total enforcement team of just 681 officers, the outcome is hardly surprising.

It is disappointing that the environment chief has sought to play down the problem, saying the ban is not intended to bring a significant improvement in air quality. Legislation not duly enforced is no more than text in the law book. Slack enforcement does not do justice to those who spent more than 14 years getting the ban in force. It is time for enforcers to act tough rather than leave the law idling.