Nice thread about headlights and fuel consumption, but I think we didnt take into account the whole cycle.
If you have your headlights on, thede's a somewhat (debatable amount) smaller chance you'll hit something or be hit during daylight hours. So there will be a (hard to compute) certain number of cars that won't be damaged or totaled, and fewer people injured or killed. If there's even a 5% lower chance of damages, we should apply that 5% to decreasing the extra cost of extra fuel. Or put it on an energy basis, how much energy does it take to repair or build new cars to replace those damaged by not using daytime lights.
I'll leave it to some armchair statistician to do *that* math.