This graphic is from Transport for London's current campaign to ask vehicle drivers to avoid idling their engines. They say that if you're stopping for a minute or more, you're better off switching off. The full version of this graphic, with more facts and figures, is here.
I've always thought it would be good if drivers at the Peahen junction, and the Watsons Walk junction further down London Road, switched off while they wait. Even when traffic is moderate, you'll often be stationary at these junctions for well over a minute. And these junctions are severely polluted, needing all the help we can give them.
What about signs at these junctions, asking and then reminding drivers to switch off their engines while they wait?