I will agree that shutting down idling vehicles can really go a long way in reducing fuel consumption.
To go beyond taxi's and big rigs I would also throw police cars into the discussion. Police idle vehicles a lot. I've been told the reason the need to idle is because their computer systems in the vehicles draw a lot of energy. The addition of a suitable battery in the trunk of a cruiser to run their systems could probably be implemented. Albeit the extra weight of the batteries might affect performance.
Individual drivers need to do their part as well. One of the things that bothers me the most is seeing 5 or 10 cars in a drive-thru line up at a fast food place or a coffee shop while the servers inside the place are serving no one. People need to start parking their cars and going inside to get what they need.
Research is what I'm doing when I don't know what I'm doing!