It is a hot and muggy morning and the street is already full of traffic. You pull in to the kerb on a single yellow line and your wife gets out and nips into a convenience store. There are no parking spaces in sight and the children are getting restless in the back seat. What is more natural than to sit and wait a few minutes with the air-conditioning on and the engine running until she comes back? It is a scene familiar to many motorists in Hong Kong but one that could soon become a driving offence under government proposals for a ban on idling engines. The move is among a series of measures to tackle the city's worsening air pollution being launched by Chief Executive Donald Tsang Yam-kuen, who has pledged to put concern for the environment at the heart of his policymaking. It comes as a number of cities and regions around the world enact similar bans in efforts to improve air quality for citizens and help meet United Nations emissions reduction targets. Earlier this month, the Canadian capital Ottawa introduced a ban on motorists idling their engines for more than three minutes that comes into force in September backed with a C$100 (HK$720) fine. In southern Taiwan, a ban will be introduced next January which also sets three minutes as the limit, while Scotland's second city Glasgow, which launched a ban in 2004, recently began imposing #20 (HK$310) fixed-penalty fines after drivers failed to respond to a 'softly softly' approach based on persuasion. In Egypt, tourists visiting the pyramids near Cairo now have to switch off the engine or face being charged with 'damaging archaeological sites' after an idling ban was imposed around the Saqqara site last October. The Egyptian authorities said the action was necessary because the idling of tour bus and car engines had caused cracks in the Djoser pyramid, which is considered the world's oldest large-scale stone monument. Momentum for legislation to bring in a ban in Hong Kong has been building since the Legislative Council backed the idea in December 2005 as one of 16 proposed measures to address deteriorating air quality in the city. Legislators were told last October by the Environment, Transport and Works Bureau that a consultation was in the pipeline for 'early 2007'. But earlier this month, an EPD spokeswoman said the government now planned to consult the public mid-year about proposals to ban idling vehicles. For some environmental campaigners, the progress has been too slow. Impatient with the pace of change, green group Clear the Air Hong Kong started its own roadside patrols a year ago targeting drivers to raise awareness of the issue. Teams of activists approach stationary vehicles and show the driver a placard with the slogan, 'Let's switch off the motor now' on weekly patrols that have been held in areas including Central, Causeway Bay, Sham Shui Po and Tung Chung. Co-ordinator Amy Ng Yuk-man said one aim of the patrols was to provide information to the EPD that would be helpful in drafting a workable law on banning idling engines. 'One of us will go up to the window and smile and normally I just gesture to say, 'Turn off your key' with my hand,' she said. 'The other person will record the licence plate and what the response of the driver is. If they don't [switch off the engine], we will take a video or a picture of the car. 'Generally the response has been good bearing in mind we started in October so the weather was cooler,' she said. 'But on the hotter days, the drivers, especially the minibus drivers, taxis and tour buses are likely to ignore us and not switch off their engine. They come up with a myriad of different excuses. 'We have taken pictures of all these types of situations and we post them on our website. And with all the video footage and photos, we have gathered them up and given them to the EPD, just to let them know what is happening during the patrols and what the responses of the drivers are.' Philip Heung Fu-lap, vice-chairman of Clear the Air, said the group wanted to see a comprehensive legal ban that applied to all classes of vehicle and all areas of the city. 'Once you have any exemptions, people will try to find a loophole so that they don't have to comply with the law,' he said. 'And it doesn't make sense to have a partial ban limited to certain areas. Air travels freely around the city and polluted air from one area may end up in another, as we have seen with air pollution from China blowing into Hong Kong. 'Our view is that the ban should commence from the moment the driver has parked their vehicle and I think a fixed penalty would be the most practical sort of fine. It should be around HK$200 to HK$250.' However, critics say the practical difficulties of enforcing a legal ban would be so costly in terms of policing and court time that it would be virtually unworkable. Andrew Windebank, chief executive of the Hong Kong Automobile Association, said: 'Yes, it's a lovely idea because obviously you do burn less fuel. 'But my view is that it's almost impossible to frame the law in a meaningful way and that will make it very difficult to enforce. And the axiom that a bad law is worse than no law is very true. 'How do you police it? Do you have a traffic warden there with a digital stopwatch? If so, would you need to have two traffic wardens so the second one is a witness to the first? 'And do you need a piece of specific equipment, which can actually determine whether the vehicle has stopped and how many seconds after that the engine was turned off? 'If you don't have this sort of accuracy, it then comes back to human error. A good lawyer in a magistrates court could run rings round this sort of legislation, if it is not drafted properly. 'You are looking at something that is going to make a very, very small impact and they are spending an awful lot of time and public money on it. Really they would be better off trying to educate people on the benefits to themselves and to the environment of switching off the engine.' In his election platform in February, Mr Tsang pledged to bring in legislation to ban idling engines but added a rider that the prospective law could be limited to 'particular hours and particular zones'. A government source said this week that ministers were leaning towards a blanket ban in which exemptions were minimised, since these would only cause confusion during enforcement. Government resolve on the issue has stiffened after its first attempt to put forward a legal ban on idling engines in 2000 failed to win community support. The EPD dropped proposals for legislation and instead issued a set of non-binding guidelines on idling engines for the transport trades in 2002. The rules allow the first five taxis and the first two public light buses at a stand to keep their engines idling, while buses are allowed to idle for five minutes before setting off, and whenever passengers are on board, embarking or disembarking. Tour buses, school buses and private light buses are given 10 minutes with the engine switched on before they set off. Various types of goods vehicle - including concrete mixers and dumper trucks - are allowed to idle when they are stationary but their equipment is switched on. Notably, however, they are not supposed to idle the engine so the air-conditioning can be kept on for the comfort of the driver. Nevertheless, the number of complaints against fumes from idling vehicles lodged with the EPD have more than doubled in the five years from 2002 to reach 501 for last year. The vehicles that caused most annoyance to the public last year were tour buses and school buses, which prompted 144 complaints, followed by goods vehicles on 141, while taxis caused the least offence, with just six complaints lodged. Commercial operators have traditionally been the staunchest opponents of a legal ban. But recently released studies and monitoring data have underlined the gravity of the air pollution issue in Hong Kong, and there are some early indications that resistance to a ban from the industry may be softening. Record levels of haze and smog were logged last year by the Observatory, with the number of days when visibility was reduced to less than 8km adding up to about a third of the year. It was also the joint eighth-hottest year on record. And a study commissioned by think-tank Civic Exchange cast doubt on residents' habit of blaming emissions from over the border for the city's poor air quality. It found that emissions released within Hong Kong were the main factor in determining air quality on 53 per cent of last year's 324 polluted days, with roadside emissions and marine traffic the largest factors. Leung Hung, of the Hong Kong Kowloon and New Territories Public Maxicabs and Light Bus Merchants United Association, said the group supported the plan and believed the current queuing guidelines for public light buses were reasonable Asked if the drivers would worry about complaints from customers when they switched off the engine, Mr Leung said: 'We have nothing to do with that. For the sake of environmental protection, everyone must agree with the plan.' Ho Hung-fai, spokesman for the Hong Kong Dumper Truck Drivers' Association, said: 'I would support a ban on idling engines. However, if the government wants to make it into a law, I think they must listen to the many drivers' groups and what their particular problems are.' Some sort of solution was needed for drivers who had to queue outside city centre construction sites amid hot and dusty conditions while other trucks were inside. 'It may be 30 degrees outside and inside the driver's cab the temperature may be 40 to 45 degrees,' he said. 'They simply can't sit inside the driver's cab when the air-conditioning is switched off.'