Near where I work, a bus waits every hour for five to ten minutes with its engine running, summer and winter. Vehicles wait in long traffic queues and at level crossings and roadworks for periods of time when the engines could easily be switched off. Thankfully, the days have gone when engines could not be relied upon to start at the flick of a switch.
I have seen an example of what can be done in Germany, where drivers are required to switch off their engines while waiting at railway crossings. Perhaps the Secretary of State for the Environment can give us a lead, but ultimately it is down to every driver to do his or her bit to improve the air we breathe.