How big of an affect does 'stop and go' have when on a run?

I live in a city. Cities have traffic. Traffic involves stopping and going, wether in a car, on a bike or running. I like to run and ride my bike as cardio work out. I recently moved to a new location in the same town. I used to run on a track. It's much easier for me to just go running somewhere outside, but how big of an impact does all the stop and go at crosswalks and streetlights have?