Daytime running lights waste gasoline

from "HowStuffWorks.com [by Anonymous Citizen on March 9, 2008]

If daytime running lights were mandatory in the U.S. and all vehicles
had them how much extra gasoline would that use each year?


For several years now Canada has required all new cars sold to have
daytime running lights. Any time the car is running the headlights are
on, but the taillights and other lights are off. You have to turn on
these other lights from the dashboard at night. Studies seem to
indicate that having the headlights on during daylight hours reduces
the number of multiple vehicle accidents (although there has been some
controversy about people forgetting to turn on their other lights at
night -- a mistake that causes extra accidents, and a good example of
the "law of unintended consequences"!).
The US has not adopted this law, but if it did they would definitely
consume gasoline. Headlights require power, and a car's engine
produces power using gasoline. If you make a few assumptions, it is
possible to estimate how much gas the law would consume.

A typical headlight bulb uses about 55 watts; sometimes the daytime
running lights run at a lower wattage so they use a little less power.
Let's say the daytime running lights use 100 watts since there are two
bulbs.

To calculate the energy used, we need to figure out how much time
people will spend with their lights on. According the to NHTSA,
vehicles in the US drove 2,560 billion miles in 1997. We need to make
a guess at the average speed people drive including stops in order to
figure out how much time people spent driving their cars. Let's guess
30 mph, which means each mile takes two minutes. That makes 5,120
billion minutes or 85.3 billion hours. Now if each car normally drives
at night about half the time, that means that the daytime running
lights would be on 42.6 billion hours a year. Multiplying by the 100
watts we get 4,260 billion watt-hours or 4.26 billion kilowatt-hours.
The U.S. uses about that much electricity nationwide in 12 hours.

Now we need to figure out how much electrical energy we can get out of
a gallon of gas. A gallon of gas contains about 60 kilowatt-hours of
chemical energy, but this energy has to go through two conversion
processes before we can use it in a light bulb. First the chemical
energy must be turned into mechanical power by the engine of the car.
Car engines don't do this very efficiently -- only about 25% of the
chemical energy can be turned into mechanical power, and the rest is
wasted as heat. After the engine gets done with our gallon of gas we
have 15 kilowatt-hours left.

Now the alternator on the car has to turn the mechanical power from
the engine into electrical power. The alternator does this a lot
better than the engine, but it is still only about 70% efficient. In
the end we get about 10.5 kilowatt-hours of electrical energy out of a
gallon of gas.

To calculate how many gallons of gas this is, you can divide the 4.26
billion kilowatt hours of energy that the daytime running lights
consume each year by the 10.5 kilowatt-hours of energy each gallon of
gas yields. If daytime running lights were on all the vehicles in the
U.S., we would burn an extra 406 million gallons of gas each year.
That's only a couple gallons for each vehicle, but in total it is more
than all of the vehicles in the country burn in a day. At $1.50 a
gallon, that's $600 million per year. Looking at it another way, an
extra 8 billion pounds of Carbon Dioxide would be added to the
atmosphere by this law.

It's an interesting question because it shows how a simple idea like,
"let's have everyone turn on their headlights all the time" can have a
real cost when you try to implement it! Whether the benefit is worth
the cost is an important question in almost any public policy
decision.

****************************************************

Now I know some of you will question the date on the article and the
cost of a gallon of gasoline. I did too, but I have no explanation.
I'd love to know where Anonymous Citizen is buying gasoline at a $1.50
per. The rest of the article has some credibility.

On 08/14/08 11:42 am Pete E. Kruzer wrote:

> from "HowStuffWorks.com [by Anonymous Citizen on March 9, 2008]
>
> If daytime running lights were mandatory in the U.S. and all vehicles
> had them how much extra gasoline would that use each year?


<Details snipped>

I bought the DRL module for our US-market 300M and installed it myself.
This vehicle has an "automatic" headlight setting too, so all the lights
switch on when it gets dark enough outside (and when the wipers are on).

The overall cost of DRLs is minuscule compared to the total cost of
running the vehicle.

And remember that the accidents that might have been prevented by DRLs
have a cost too, a cost that may be reflected in our insurance premiums.

Perce