Diesel prices in the United States have climbed above $5 per gallon again, reviving one of the clearest warning signs for the American economy.

The increase is already visible at fuel stations, but that is only the first stage. Diesel powers the trucks that move food, construction materials, industrial goods and consumer products across the country. When diesel rises, transport costs follow. Those costs eventually reach store shelves.

According to AAA, the national average reached $5.005 per gallon on July 16. A week earlier, it was around $4.81. At the same point last year, drivers were paying roughly $3.73.

Since the conflict with Iran began, diesel prices have risen by about one-third.

Renewed tensions in the Persian Gulf have added fresh pressure to global energy markets. Lower tanker traffic through the Strait of Hormuz, reduced refinery capacity and concerns over supply have all contributed to the latest rise.

But the problem is larger than one conflict.

Restrictions on Russian diesel exports, attacks on Russian refineries and low US distillate inventories have tightened the market further. American diesel stocks have fallen close to levels not seen in decades, leaving little room for disruption.

For many Americans, the price displayed outside a fuel station is one of the most immediate measures of economic stress. It affects family budgets directly, but it also influences the price of nearly everything transported by road.

The United States depends heavily on long-distance trucking. Much of what Americans buy spends at least part of its journey on a diesel-powered vehicle. Freight companies may absorb higher fuel costs for a short period, but not indefinitely. The increase is passed to distributors, retailers and finally consumers.

That creates a new problem for Washington.

Higher diesel prices could push inflation upward again, especially in food and goods. Official data may take weeks to reflect the change, but consumers will see it sooner in delivery charges, grocery bills and retail prices.

Diesel has crossed the $5 mark again. The first shock is at the pump. The larger one will appear everywhere else.