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Welcome to the forum Audry!
I have a friend who worked in traffic engineering. He says the effect you describe is known generically as a traffic wave. It's usually used to describe those "slowdown" areas you find on the freeway, but also applies to vehicles starting up after a light turns green.
The basic idea is that the cars lined up at the red light could all start moving simultaneously, but that never happens due to driver lag time.
Interestingly, I read an article in Discover magazine that talked about "smart" cars, where the delay you describe could be avoided by having the cars linked via some wireless technology. It would sense when each car starts moving, and communicate that to the next car, allowing more simultaneous motion when the light changes. It would save both time and gas, and they project it could become available in a model year or two.
thanks for the term!
I remember I was probably around 10 or 11 the first time I ever thought about this phenomenon. I was in the car with my uncle, and he said something to the same effect - that if everyone could start at the same time, we'd all get going faster. I agreed with him, but later thought that it would be impossible to eliminate the lag completely, because people leave a lot more space between cars while moving than they do while stopped. The time between one driver starting and the next is needed for the cars to spread out.
Yeah, that's the way traffic wave is usually used, but it's the same effect when cars start up at a light change.
Driver response lag, desired vehicle spacing, and vehicle acceleration (or braking) capabilities all come into play. In moving traffic, the wave is already in motion relative to the cars. At a light, the wave is just starting.
If you're looking for a term specific to cars starting up at a light change, I don't know it. Maybe someone else on the forum does. In the meantime, you could use the kinematically descriptive term vehicle response lag. But I fear that's not what you're looking for.
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