The biggest truckload carrier in the U.S. appears to be back in the market for acquisitions.

Knight-Swift Transportation Holdings Inc. said Friday it is acquiring Richmond, Va.-based Abilene Motor Express for an undisclosed sum, bringing more capacity under the company’s control as strong shipping demand in the U.S. is driving up freight rates and carrier earnings.

The buy in the first for Phoenix-based Knight-Swift since Knight Transportation completed its purchase of Swift Transportation last September, marking the biggest consolidation in several years in U.S. trucking. Before the purchase, Swift was the largest carrier in the truckload market, in which carriers haul full loads on trucks on long distances for a single customer, and Knight was No. 2.

The combined business now holds about 2% of the highly fragmented market, according to estimates by the SJ Consulting research group, which said the biggest 25 carriers by revenue split only 13% of the market.

Abilene brings Knight-Swift a business that includes 400 trucks and an estimated $100 million in annual revenue, as well as drivers in a market where trucking companies are reporting difficulty in finding workers.


Knight-Swift said in a securities filing that the business has an operating ratio “in the low 90s,” indicating its operations are profitable.

KeyBanc Capital Markets wrote in a research report Friday that the buy would add an estimated $0.02 to $0.03 per share to Knight-Swift earnings. It also signals, KeyBanc wrote, the carrier is potentially in the market “for additional tuck-in acquisitions.”

The trucking market has been growing rapidly as a robust U.S. economy has spurred shipping demand, leaving capacity for long-haul services tight and pushing companies to pay more to move goods.

DAT Solutions LLC said the national average spot market rate for vans, the most common type of truck transport, was $2.13 per mile, down 11 cents from January but about 52 cents per mile higher than it was a year ago.


Trucking companies also are reporting big gains from the new U.S. tax law, and Knight-Swift said the tax benefits added $364.2 million to its bottom line in the fourth quarter of 2018. Analysts have said the stronger financial footing may push more companies to spend the gains on mergers and acquisitions.

Write to Paul Page at paul.page@wsj.com