Post by ***@aol.com55 mph would save billions of gallons of oil, billions of dollars and
thousands of American lives.
These claims sound impressive until you look at them in context. You
need to be sure to include lost earnings due to time spent in longer
commutes. Extra gas wasted in traffic jams. Portions of lives spent in
cars instead of other activities, etc.
Gas savings:
Dropping the speed limit on highways from 65 and 70 to 55 is not going
to effect average speed of traffic by 10 or 15 mph. Most trips are at
significantly lower speeds on secondary roads and streets. So you are
only going to effect the fuel economy on a small portion of all trips.
It is my guess (and only a guess) that speed limits higher than 55 mph
only affect around 25% of all the miles driven by typical,
non-commercial, drivers. Say that total passenger car / light truck
miles driven in a given year is around 3 trillion miles. This means
the speed limit will have an effect on about 750 billion miles. The
average fuel economy of non-commercial passenger vehicles in the US is
around 20 mpg. I am guessing the average fuel economy of a car driving
a steady 65 is going to be in the high 20s - lets pick 27 (a guess).
Assume you drop the speed limit to 55 on the 25% of miles traveled
where the speed limit is 65 or higher. What do you think the fuel
economy improvement will be? It could be as great as 10% (but probably
less). Lets say the steady state fuel economy at 55 is 30 mpg. So to
go 750 billion miles at 65+ you will use somewhere around 27 billion
gallons of oil. To do the same number of miles at 55, you will use
somewhere around 25 billion gallons of oil. A savings of 2 billion
gallons. The US consumes over 140 billion gallons of gasoline a year.
So 2 billion gallons is a savings of less than 1.4%. Of course this
does not include the gallons consumed because of time lost in the stop
and go traffic that will result because the lower speed limits reduce
the capacity of the highways. I suspect when all is said and done, you
might save 1% of the gasoline consumed in this country by reducing the
speed limit to 55.
Fatality reduction:
Let's guess that the average high speed trip (trips where speed limits
higher than 55 mph have an effect) is 30 miles (again, just a guess
for illustrations). Assume that 25% of the trips fall into this
category. Dropping the speed limit from 65 to 55 will increase the
length of such trips by 5 minutes. The cumulative effect will be that
people spend 125 Billion more minutes in cars. This is 2.1 Billion
hours, or 87 million days, or 238 thousand person years, or the life
span of about 3,400 people. So you are effectively killing off 3,400
people each year by forcing people to spend more time in their cars. I
content that lowering the speed limits will not reduce the accident
rate significantly. Most accidents don't occur on open stretches of
highway. Most occur on streets that have much lower speed limits and
at intersections. If you want to reduce highway fatalities I think you
should concentrate on aggressive drivers, people who run stop lights
and signs and people who are incompetent drivers.
Monetary savings:
The extra 2 billion gallons of gas used because of higher speed limits
will cost 6 to 8 billion dollars. How do you value a person's time?
Lets say time is only worth $5 per hours. The extra 2.1 billion hours
spent in cars translates to over 10 billion dollars. So, where is the
dollar savings? People that don't value their time, can drive slower
and take more peaceful routes. It is not fair for you to decide that I
should waste more of my time so that I can save what I consider a
trivial amount on gas. It is not up to you to decide that I should
waste significant portions of my life in cars because of a very very
small increase in the risk of a crash related to the higher speed
limits.
If you want to drive slower, drive slower. If you want to reduce fuel
consumption demand higher gas taxes.
Ed