Sen. Clinton’s Untimely Proposal

by Don Boudreaux on June 2, 2006

As a means of conserving oil, Sen. Hillary Clinton wants Uncle Sam again to mandate a maximum speed limit of 55 MPH. Presumably she’s aware that lowering the speed limit will cause us to spend more time on the roads and less time at our destinations.

But on her website, Sen. Clinton expresses concern that Americans are strapped for time: “Today’s families are often stretched thin – working to make ends meet while also trying to carve out time to care for their young children and aging relatives.”

Assuming consistency across her various policy positions, we can conclude that Sen. Clinton is confident that the value of the time that a 55 MPH speed limit will force us to waste on the roads is worth less to us than oil we’ll save by driving more slowly.

Let’s explore. Assume that the typical car on the road today gets 25 miles per gallon on the highway and that a gallon of gasoline costs $3.00. Further assume (rather generously) that driving more slowly will increase the typical car’s fuel efficiency from 25 mpg to 35 mpg.

On highways where the speed limit currently is 75 MPH, reducing the speed limit to 55 MPH will cause a driver to cover 20 fewer miles in one hour of driving. To travel these 20 miles at 55 MPH will take 21.82 minutes. That is, the distance a driver covers in one hour driving at 75 MPH requires 81.82 minutes to cover while driving at 55 MPH.

At today’s average hourly wage rate for non-supervisory workers of just over $16 — but let’s call it an even $16 — this 21.82 minutes is worth $5.82. (That is, working at a wage rate of $16 per hour, a worker will earn $5.82 in 21.82 minutes of work.)

But how much does the driver save, fuel-cost-wise, by driving more slowly?

Driving at 75 MPH (and getting 25 mpg) costs the driver $9 of gasoline per 75-miles driven. (Remember that gasoline is priced at $3 per gallon.) Driving at 55 MPH (and getting 35 mpg) costs the driver $6.42 of gasoline per 75-miles driven.

In short, for every 75-miles covered on a highway, reducing the speed limit from 75 MPH to 55 MPH will save a driver $2.58 in fuel cost — and this assuming that the increase in fuel efficiency of the average car caused by the lower speed limit is a whopping 10 mpg. But the resulting greater time on the road will cost a driver earning the average non-supervisory wage $5.82 worth of his or her time per 75-miles driven.

The net cost to the average worker driving the average car will, under the above reasonable assumptions, be about $3.24 per 75-miles driven. Not a good deal, Sen. Clinton.
……

Here’s a challenge for a clever student: assume (as is reasonable) that an enforced speed limit of 55 MPH will cause the price of gasoline at the pump to fall. By how much would it have to fall (under the above assumptions) in order to make the $$$ saved on gasoline exceed the $$$ value of the extra time spent driving?

{ 12 comments }

1 Xrlq 06.02.06 at 5:07 pm

Even the assumption that an enforceable 55 mph speed limit will save gas is probably more limited than most people think. While a few people might compensate for the slower commute by moving closer to work, most will not, so as a general rule, the same number of vehicles will go on the roads every day, with each staying on the roads longer. That, in turn, will exacerbate congestion everwhere. And we all know what wonders stop and go traffic can do for fuel efficiency.

2 Mike 06.02.06 at 5:41 pm

I also suspect that more people will receive speeding tickets, as they, like drivers in Los Angeles, put the pedal to the metal when on a non-congested part of the highway.

3 Griffin3 06.02.06 at 6:44 pm

I assume you set up your ‘exercise for the student’ as a joke. Quite simply, if all this driving 55 causes the gas price to drop, the amount of gas saved is worth LESS, and therefore will never be equal to the dollar value of time lost.

If you assume the price of gas rises due to external factors, then you will eventually hit a break even point. As near as I can rough it it out without setting up an equation, the gas price has to rise to $6.76 before Ms. Clinton’s idea makes sense, assuming the rest of the numbers are true.

From what I recall of high school physics, if you assume no rolling friction, the gas mileage at 55mpg should be, hmm … 36% better, or 34 mpg. So that’s not too far off. In my experience, it’s a hair worse than that, because rolling friction is not zero, part of your power is used to run your AC and alternator, etc., and life just doesn’t follow a physics equation. Although, it might be more telling that all these cars are rated by the EPA at a rather quaint 55 mph; so it might be better to think of the average mileage to be 25 mpg, and mileage at 75 to be more like 18 mpg.

[GEEK ALERT: The oft-repeated assertion that driving twice as fast quadruples your gas consumption is misleading enough to be considered junk science. Although technically true that your fuel-per-time squares, your distance traveled increases proprotional to speed, and so your mpg decreases only linearly compared to your speed (as in, a straight-line tradeoff.)]

And any remaining folks that say that driving 55 saves lives are mistaken; many studies have shown that overall accidents remained dead steady at 1.2 per million man-miles driven (although fatalities have decreased a hair due to seat belt use and marginal safety improvements.)

4 Supremacy Claus 06.02.06 at 9:25 pm

Don: You pose a 5th grade math word problem. The math knowledge of the lawyer stops at the 4th grade, that needed to count one’s own money.

It is out of the question that Hillary Clinton will ever be able to follow what you are trying to say.

5 Stephen Macklin 06.03.06 at 8:52 am

I can attest that there are two basic speeds driven on I95 in CT. Depending on the time of day, cars on one side of the highway will move at an average speed approaching 6 mph. The opposite side will be averaging about 75 mph. The posted speed limit is only relevant for the determination of how big your ticket will be.

6 mgriffinwalters 06.03.06 at 9:09 am

Since I happen to be a student, I took up your student math problem. Based upon your very generous assumptions, the price of gas would have to fall to $1.48 to break even. That means it would have to fall a full 50% in order to hit that mark.

Since it’s unlikely that the minute amount of gas savings experienced by enforcing such a speed limit would actually amount to anything even close to this.

The underlying reason for high gas prices is high oil prices. Though gas use makes up a fair chunk of oil usage, there are many other things, such as energy production, that use it. And, unless we forget, oil, and gas to a lesser extent, are traded on a world market. Therefore, it’s unlikely that this kind of action would amount to more than a drop in the bucket. That is, unless you account for the ability of pathetic politicians to claim that they “did something.”

7 MightyWaldo 06.03.06 at 1:12 pm

This sort of argument is often thrown around to justify time-saving techniques (or lambast time-wasting ones). For your argument to hold up, however, it is not enough to specify hourly wages; the person in question must actually be able to earn the money. In other words, assuming that the person left for work at the same time in both cases, and returned home at the same time, the extra 22 minutes per hour you specify might enable that person to earn the extra $6. If they are paid from 8 to 5, however, they earn exactly $0 if they show up a little early or leave a little late.

Now, the time you (or this special person) spend on all of the non-commute trips, such as the drive to gramma’s house, would not have the earning power you note (assuming that you are already working the hours you can for the wages you can pull down), so the argument becomes less powerful. Note, of course, that you already receive recompense for any time spent driving on the job. And, of course, those poor fools like me who work for a set salary don’t have the option of earning additional money by working more hours.

You could argue that your hourly wage indicates the value that you put on your time, in which case the argument (somewhat) holds water. Instead, however, you could argue that the speed limit is the (supposed) maximium, unless you are in California, in which case it appears to be a minimum. Thus, those people who want to save fuel (and/or money from buying same) can simply drive at 55 in the right lane. Anyone think that they’ll be passing Senator Clinton and her entourage driving at 55? I, perhaps cynically, believe that she’ll take the opportunity to save driving time, where legal, and drive at the limit, even if it’s above 55, because she’s an important person with places to go and things to do. Unlike the unwashed mob she’s trying to protect.

8 J.T. Wenting 06.04.06 at 9:45 am

In other words Waldo, you value a person’s time with his family to be worth nothing at all?

9 MightyWaldo 06.04.06 at 11:46 am

So you agree that your time with your family is worth $16/hour, J.T.? Why not some other arbitrary number, like $100/hour, in which case the reduction to 55 mph would cost you serious money? Of course, if your time with your family is worth $100/hour to you and work only pays you $16/hour, then, by the argument used in this posting, you are losing money every hour you work, right?

What I said was that no one will pay you for the time that is lost, not that the time itself is worthless. As such, the argument about specific value lost (particularly when calculated to the penny per hour) is…less than convincing.

I then tried to point out better justification for not changing the speed limit: it’s completely unnecessary. You can already choose to drive at the lower speed.

By the way, there is one change that apparently results in an immediate 12% drop in traffic accidents every year: the Fall time change. (The Spring time change has the exact opposite effect.) If we are looking to reduce traffic accidents, let’s just “fall back” every day. By Congressional calculation methods, that’s be (12%*365 =) almost a 4400% reduction in accidents!

10 Mr L 06.04.06 at 11:19 pm

What I said was that no one will pay you for the time that is lost, not that the time itself is worthless. As such, the argument about specific value lost (particularly when calculated to the penny per hour) is…less than convincing.

Well, not quite. Even though you aren’t paid, that extra driving time has an easily determinable monetary value. Just look at what people are willing to do to reduce the time of their commute — risk speeding tickets, pay hefty tolls on the expressways, live closer to the office, etc. — and you can get a pretty good idea of the ‘real’ cost.

To give an example, if I pay $5 on the expressway to shave a half hour off my commute, then my time’s worth at dead minimum $10/hr.

11 Jimmy Antley 06.05.06 at 4:23 pm

Good comments, but I’d like to add, in response to Mr. L.:

People don’t drive above the speed limit just to save time. It does not feel good going 55 mph on a road in which you feel safe at 80 mph. Most of the time, I feel the need for speed even if I’m running early and will have to sit at the destination for a half hour waiting; traffic tickets are a bit of a disincentive, but what’s the chances of that happening.

Maybe some people feel good about saving their gas money, and that feeling overpowers the other feeling of poking along the road like at 55 mph like an idiot, but I really can’t relate.

I save lots of gas money by not having a commute (I’m probably driving only 6000 miles annually.) But when I get on the road I’ve just gotta move. To quote Sammy Hagar, “I can’t drive fifty-five!”, and Hillary can just eat my dust…

12 nofixedabode 06.05.06 at 7:45 pm

As I survivor of the 70’s, I can’t recall that the 55 mph speed limit ever reduced the price at the pump. But it says something about Hillary that the best she can offer is Nixon era solutions!

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