there definitely is such a curve. I just can't imagine its optimum is at 5+ seconds between cars, at least at the highway speeds we drive in dense/often congest

there definitely is such a curve. I just can't imagine its optimum is at 5+ seconds between cars, at least at the highway speeds we drive in dense/often congested areas (~60mph / 100kph where I live). Intuitively I'd put it around 3 seconds.