ANN ARBOR – Michigan motorists are getting hit with another cost shock just as the summer driving season ends — and with the midterm elections approaching, soaring fuel prices could become another test of how voters judge the economy.

Michigan regular gasoline averaged $4.31 a gallon as of Sept. 12, according to AAA, up from $4.03 a week earlier and $3.08 a year ago.

That’s an increase of roughly 40 percent in one year.

But the bigger economic threat may be diesel.

Michigan diesel has climbed to $6.09 a gallon, compared with $3.68 a year ago — an increase of roughly 66 percent. National diesel reached a record $6.16.

Those diesel costs don’t stay at the truck stop.

They work their way into the cost of harvesting crops, moving food, delivering packages, operating construction equipment and transporting virtually everything consumers buy.

That makes soaring fuel prices more than an energy story.

They are becoming an inflation story — and potentially a midterm election story.

What $4.31 Gas Costs Michigan Drivers

Consider a Michigan driver who buys 15 gallons of gasoline a week.

At last year’s $3.08 average, that fill-up cost about $46.

At today’s $4.31, it costs nearly $65.

That’s roughly $18 more every week — approaching $950 over a year if that price difference persisted.

Now multiply higher fuel costs across millions of motorists, delivery trucks, contractors, farms, manufacturers and small businesses.

And that’s before considering what $6 diesel could do to the prices of the products those trucks deliver.

Consumers Are Already Feeling It

There is evidence that rising fuel costs are changing how Americans view the economy.

The University of Michigan’s closely watched Index of Consumer Sentiment fell from 51.7 in August to 47.8 in preliminary September results, down 13 percent from a year earlier.

Survey Director Joanne Hsu specifically cited resurgent fuel prices and trade tensions as consumers anticipated greater pressure on their pocketbooks.

Consumers’ expected inflation rate over the next year also jumped from 4 percent to 4.6 percent.

That’s politically important because voters don’t experience inflation as an economic statistic.

They experience it when they buy groceries, pay utility bills and fill their gas tanks.

The $6 Diesel Problem

Diesel may pose an even greater threat to household budgets because consumers pay for it indirectly.

Trucks haul groceries to supermarkets, components to Michigan factories, packages to homes and building materials to construction sites.

Businesses facing sharply higher fuel costs have limited choices: absorb the expense, cut costs somewhere else or pass at least some of it along to customers.

That means today’s $6 diesel can become tomorrow’s grocery, construction or delivery price.

For a Michigan small business using 500 gallons of diesel a month, the increase from last year’s $3.68 average to $6.09 represents roughly $1,200 in additional monthly fuel expense.

Michigan Farmers Get Hit Twice

Michigan agriculture faces an even tougher calculation.

Farmers aren’t simply paying more to fill their pickups.

Diesel powers tractors, combines and other equipment. Crops then must be trucked to grain elevators, processors, warehouses and ultimately retailers.

And farmers are simultaneously confronting sharply higher fertilizer costs associated with disruptions caused by the war with Iran.

The combination comes at a particularly bad time: Michigan’s fall harvest.

Nationally, diesel prices have risen about 60 percent since February. Farmers already struggling with tight margins now must harvest corn, soybeans and other crops with dramatically more expensive fuel.

That could have consequences reaching far beyond rural Michigan.

Higher farm and transportation expenses ultimately put additional pressure on food prices.

Could The Rural Vote Be In Play?

The farm squeeze also introduces an intriguing political question.

Rural Michigan has been an important part of the Republican coalition.

But farmers don’t have to suddenly become Democrats for economic dissatisfaction to matter politically.

Some could split their tickets. Others could become less enthusiastic.

Some could simply stay home.

That possibility becomes particularly important in close congressional races.

Nowhere is the equation clearer than Michigan’s 7th Congressional District, where Republican Rep. Tom Barrett faces Democrat William Lawrence.

The nonpartisan Cook Political Report rates MI-7 a Toss Up.

The district includes Lansing and Livingston County along with substantial rural territory in Clinton, Shiawassee and Eaton counties.

Agriculture is a significant part of that economy.

USDA’s most recent congressional district agricultural census counted nearly 8,000 agricultural producers and roughly $874 million in annual agricultural sales in MI-7, including more than 318,000 acres of soybeans and 222,000 acres of corn.

Those farmers will know precisely what diesel, fertilizer and other inputs cost them when their combines move through Michigan fields this fall.

Republicans don’t have to lose the rural vote to feel the consequences.

In a Toss Up congressional district, even reduced turnout or increased ticket-splitting among normally reliable Republican voters could matter.

From Iran To A Michigan Voting Booth

The unusual part of this inflation shock is where much of it originates.

Normally gasoline prices decline after Labor Day as summer driving demand falls and refiners switch to less-expensive winter-blend gasoline.

Not this year.

AAA says volatility surrounding the Strait of Hormuz has helped push crude oil back toward $100 a barrel.

The Iran war has also disrupted fertilizer markets, while attacks on Russian energy infrastructure have added pressure to global petroleum supplies.

That means geopolitical events thousands of miles away are reaching Michigan consumers through both the gas pump and supermarket checkout.

Pocketbook Politics Returns

Gasoline prices alone aren’t going to determine Michigan’s midterm elections.

Voters will also weigh immigration, healthcare, jobs, foreign policy and numerous other issues.

But economic anxiety is clearly rising.

And gasoline has a political characteristic almost no other consumer product possesses:

Its price is advertised in giant numbers along virtually every major road in Michigan.

Michigan voters don’t need an economist to tell them whether gasoline has become more expensive.

They can see it every morning on the way to work.

Farmers can see what diesel costs when they fill their equipment.

Businesses can see their fuel bills.

Families can see their grocery receipts.

And that could make the economic question heading toward November remarkably simple:

Can I afford my life — or my business — better today than I could a year ago?