'Science fiction': Transport companies — the backbone of economy — are sounding alarm on fuel prices

Transportation companies, the lifeblood of the U.S. economy , are flashing warning signs as diesel costs hit records.

Prices for diesel, the fuel type used to power trucks and trains, came in at an all-time high of around $6.31 per gallon on Wednesday, according to AAA . Diesel prices have surged more than 70% from a year ago, which analysts attribute to the supply shock from the U.S. war with Iran.

"We have seen some of the most radical and abnormal swings in fuel prices that I think we've ever seen," said Brad Delco, finance chief at trucking company J.B. Hunt , at an industry conference hosted by Morgan Stanley.

Delco said to expect a drop in earnings between 5% and 10% from the second to third quarter as a result of higher costs. Shares of J.B. Hunt dropped more than 13% in Wednesday's session, one of the worst days for the stock since going public in 1983.

The Dow Jones Transportation Average , a broader gauge of the sector, close to 3% on Wednesday. J.B. Hunt was the biggest loser of the index, which also includes rideshare providers and airlines.

Those diesel-related price pressures should only intensify in the coming days, warned Patrick De Haan, head of petroleum analysis at price tracker GasBuddy .

The national average could eclipse $6.50 in the next two days, De Haan said. Midwest states such as Michigan, Ohio and Illinois may see per-gallon diesel prices touch $7 in the coming days, according to his estimates.

In California, AAA found that the average rate for a gallon of diesel has already surpassed $8. Prices have climbed almost 20% in the last month alone, according to the motor club association's data.