I am not sure shutting the engine down at a stop light will help any, when you turn your engine off the water pump stops moving coolant, if you kill the engine and turn the key on so the guages come on you can watch the temp climb, as soon as you start it the temp will immediately beging to drop. Just my $.02. As everyone else has already said, keep and eye on it, try to take a route without much sitting in traffic, keep it moving and if it looks like it is going to be a problem try to find a shroud or a junk yard e-fan to get you by until you can get your new fan.