Shipments of U.S. trailers for heavy-duty rigs fell in 2009 by 44 percent from 2008 levels and to their lowest annualized levels since 1975, according to data released Friday by ACT Research Inc., a leading provider of analytical and forecasting data.

According to ACT, 78,000 trailer units were shipped in 2009. By comparison, 80,414 trailer units were shipped in 1975, when Gerald R. Ford was president and motor carrier deregulation was still five years in the future.

In a typical year with a relatively stable economy, about 180,000 trailers are shipped, according to Kenny Vieth, partner and senior analyst at Columbus, Ind.-based ACT.

Vieth said ACT forecasts shipments of about 100,000 trailers in 2010 should economic conditions continue to improve. If the economy remains moribund, that number would be reduced to 90,000, he said.

Vieth said the poor economic climate in 2009 reduced demand for new trailers and compelled owners and operators to hold on to their old trailers longer than usual. The nation's aging trailer fleet starts 2010 "one year older than it has ever been in its history," he said in an interview.

A terrible resale market for old trailers further dampened demand for new equipment, Vieth said. The lack of aftermarket demand and rock-bottom resale values has made it financially non-viable for owners to unload their trailers, he said.

"No one is anxious to trade in their trailers," he said.

Ironically, advances in trailer-tracking technology, which has enabled trucking companies to make better use of their equipment, has dampened new trailer sales, Vieth said. In years past, truckers would effectively over-order equipment because their inability to track the status of any one trailer required them to keep equipment in reserve. Tracking technology, which became mainstream in the mid-2000s, made it easier for truckers to monitor their equipment and lessened the need to keep what might be considered buffer stock, Vieth said.