Americans are spending $2.4 billion less on gasoline per week than they were a year ago. But how is this affecting your retirement and state budgets? The Post's Chris Mooney breaks down the downsides to cheap gas. (Gillian Brockell/The Washington Post)

The oil price revolution continues. West Texas Intermediate crude oil, a U.S. benchmark, is around $47 a barrel this morning, compared with over $107 per barrel in summer 2014. It has literally lost more than half its value in under a year.

Regular gasoline, meanwhile, is down to $2.05 per gallon nationally averaged, versus $3.28 a year ago. That's a stunning plunge that has now gone on for well over 100 days -- a new record, according to AAA. More than 20 U.S. states are now averaging below $2.00 per gallon for regular gasoline.

All of this, as economists have repeatedly noted, represents a vast savings to the average U.S. consumer. According to the Energy Information Administration, U.S. consumers are expected to save $550 per household on gasoline in 2015, relative to their spending in 2014. According to AAA, consumers could save as much as $75 billion overall on gasoline this year.

Source: AAA.

All of which sounds, frankly, awesome. But it’s worth asking: Could anything possibly go wrong here? Is there any downside, at all, to cheap oil and the resultant cheap gasoline?

Here are some downside ideas that have been proposed, and some thoughts on how seriously you should worry about them:

Could cheap oil prices hit your retirement account or 401(k)? 

One concern is that cheap oil prices are driving market volatility that could hurt people's retirement accounts. However, this concern doesn't seem to carry a lot of weight, at least at this point in time.

I mean, sure, if a person were exclusively or mostly invested in oil stocks or oil intensive funds, then yes, their 401(k) is probably worth less now than it was six months ago. So for instance, ExxonMobil stock is down from highs of close to $105 in the summer to around $91 today. And Chevron is down from nearly $135 in July to $105 now.

But this is precisely why investment advisers tell us to diversify, diversify, diversify, and invest for the long term. Overall, although there has been considerable market volatility of late, we’ve been in a rising market over the past year (and indeed, ever since the market’s low in 2009). Oil stocks aside, if you look at the Dow Jones industrial average over the last year, or the S&P 500, stocks are very clearly up, not down.

That’s because while oil majors like Exxon and Chevron are key components of the Dow, so are many other kinds of stocks ranging from Nike to IBM. And as far as oil prices go, in many cases, these companies may be saving money on various kinds of transportation/operations costs -- or consumers may have more money to spend on their products.

So as far as 401(k)s go, this is really a moment that underscores the importance of portfolio diversification. And if you are diversified, then you are probably up overall, just as with the general market.

Are cheap oil prices hurting state budgets?

Another concern is that some really oil-dependent U.S. states are going to be badly hurt by this dramatic economic shift. And there's no doubt that some states whose economies depend a lot on oil are going to be affected. At the top of the list is Alaska, where half of the state budget has depended on taxing oil production, and which has already seen budget shortfalls which could trigger cuts in state government and spending on state services.

In other states with really big oil industries, such as Texas, there have already been lost jobs as well. But the point is that there are winners and losers, and there will be a lot of winners in other states that are not so energy dependent.

Is cheap gas making us buy less fuel efficient cars?

For liberals, one major fear is that so much cheap gas will bring back bad driving habits – and big, bad, fuel-inefficient vehicles. The concern has merit: Economists would definitely say that, as oil and gas get cheaper, the incentives are for people to drive more, and to purchase more gas guzzlers. In fact, that is already happening. SUV sales were up 12 percent in 2014, according to the National Automobile Dealers Association.

Moreover, according to the University of Michigan's Transportation Research Institute, the average fuel economy of newly purchased vehicles has actually already slipped due to decreasing gas prices, from 25.3 miles per gallon in Sept-November 2014 to 25.1 miles per gallon in December 2014. And it was really high, 25.8 per gallon, back in August.

Hummers on the lot at a dealership in Tustin, Calif, in 2009. AP Photo/Mark Avery

So declining gas prices already mean people are buying cars that guzzle more. And actually, the same researchers have already found that the emissions per individual driver have also gone up (again, since an all-time low in August).

It is important to emphasize, though, that overall, vehicle fuel economy has really improved a ton since 2007, and emissions have gone way down. In that context, these recent changes are merely slight regressions and don’t dramatically mar that trend – yet.

But the longer this goes on, the more super-low gas prices will shape behavior. So this turns out to be a pretty legitimate concern.

Will cheap oil and gas doom the Keystone XL pipeline?

At least if you're a pro-Keystone XL conservative, you might be worried that the dramatic plunge in oil prices weakens the case for the pipeline.

But actually, that may not be true either. If anything, you could argue that lower oil prices make Keystone XL more attractive, at least for oil producers. The reason is that shipping crude oil by pipeline is generally cheaper than shipping it by rail, and that savings matter more (not less) with low oil prices. According to the Congressional Research Service, shipping oil by rail may be about $5 to $10 per barrel more expensive than shipping it by pipeline.

Will consumers hold on to their gasoline savings, rather than spend them?

The newest concern, which has been buoyed by disappointing retail sales numbers from last week -- which showed an unexpectedly big decline -- is that lower gas prices might not actually help the economy as much as forecast, because consumers will save the extra money, rather than spending it. But this seems pretty unlikely.

First, it's very possible that last week's sales numbers were a temporary blip. And in the long term, when consumers have more money in their pockets -- much like when they get a tax cut -- they can be expected to both spend more and, in some cases, save more, depending on the individual. But it's not clear why saving would be the only thing Americans would do with extra money.

So in sum, there are some very real downsides to cheap gas prices -- especially when it comes to vehicle fuel economy, and for certain states and sectors. But that's not the same as saying that it's a major problem overall for the U.S. economy, or that the downsides outweigh the upsides. U.S. consumers, and the U.S. economy, should prosper overall.

Americans are spending $2.4 billion less on gasoline per week than they were a year ago. But how is this affecting your retirement and state budgets? The Post's Chris Mooney breaks down the downsides to cheap gas. (Gillian Brockell/The Washington Post)