infogic commented on YSK: A car takes uses about seven seconds worth of fuel to start up. If you are going to idle for a period of time longer than that, you'll save fuel by turning your engine off. • youshouldknow •
In some cities in my country (maybe all) it is regulated and fined to idle your car over 1 min, the point of it I think is to make people used to turning off their cars for train crossings and bridge openings.