WASHINGTON — On a clear, dry June evening in 2015, cars and trucks rolled slowly in a herky-jerky backup ahead of an Interstate 75 construction zone in Chattanooga, Tenn. Barreling toward them: an 18-ton tractor-trailer going about 80 mph.

Despite multiple signs warning of slow traffic, the driver, with little or no braking, bashed into eight vehicles before coming to a stop about 1½ football fields away. Six people died in the mangled wreck and four more were hurt. The driver was convicted of vehicular homicide and other charges last month.

In response to this and similar crashes, the government in 2016 proposed requiring that new heavy trucks have potentially life-saving software that would electronically limit speeds. But now, like many other safety rules in the works before President Donald Trump took office, it has been delayed indefinitely by the Transportation Department as part of a sweeping retreat from regulations that the president says slow the economy.

An Associated Press review of the department’s rulemaking activities in Trump’s first year in office shows at least a dozen safety rules that were under development or already adopted have been repealed, withdrawn, delayed or put on the back burner. In most cases, those rules are opposed by powerful industries. And the political appointees running the agencies that write the rules often come from the industries they regulate.

Meanwhile, there have been no significant new safety rules adopted over the same period.

The sidelined rules would have, among other things, required states to conduct annual inspections of commercial bus operators, railroads to operate trains with at least two crew members and automakers to equip future cars and light trucks with vehicle-to-vehicle communications to prevent collisions. Many of the rules were prompted by tragic events.

“These rules have been written in blood,” said John Risch, national legislative director for the International Association of Sheet Metal, Air, Rail and Transportation Workers. “But we’re in a new era now of little-to-no new regulations no matter how beneficial they might be. The focus is what can we repeal and rescind.”

Trump has made reducing regulations a priority, seeing many rules as an unnecessary burden on industry. Last month he tweeted that his administration “has terminated more UNNECESSARY Regulations, in just 12 months, than any other Administration has terminated during their full term in office ...”

“The good news is,” he wrote, “THERE IS MUCH MORE TO COME!”

The Transportation Department declined repeated AP requests since November for an on-the-record interview with Secretary Elaine Chao, Deputy Secretary Jeffrey Rosen or another official to discuss safety regulations. Instead, the department provided a brief statement from James Owens, DOT’s deputy general counsel, saying that new administrations typically take a “fresh look” at regulations, including those that are the most costly.

The department’s position has been that it can reduce regulation without undermining safety. And DOT officials have questioned whether some safety regulations actually improve safety.

“We will not finalize a rule simply because it has advanced through preliminary steps,” the statement said. “Even if a rule is `one step away,’ if that rule is not justifiable because it harms safety and imposes unnecessarily high economic costs, for example, that rule will not advance.”

But the rule requiring new trucks to have speed-limiting software would actually have economic benefits, according to a DOT estimate prepared two years ago. It would save as many as 498 lives per year and produce a net cost savings to society of $475 million to nearly $5 billion annually depending on the top speed the government picked. That’s nearly half the 1,100 deaths annually in crashes involving heavy trucks on roads with speed limits of 55 mph or higher. The government didn’t propose a top speed but said it had studied 60, 65 and 68 mph.

The proposal was also expected to solve another problem: Most heavy truck tires aren’t designed to travel over 75 mph, but some states have 80 mph speed limits.

Rick Watts of Morristown, Tenn., who lost his wife, two young stepdaughters and mother-in-law in the I-75 crash, said he can’t understand why the proposal has been sidetracked.

“If you’re going 80 and you’re knocked down to 60, that’s going to lower the impact,” he said. “It just stuns me that you can give these people proof and they say, `We’ll look into that.’ It just baffles me that they’re killing so many people every year.”

The American Trucking Associations, an industry trade group, has claimed credit for stalling the rule. After initially supporting it, the group now says it would create dangerous speed differentials between cars and trucks. A news release from the associations said its success in stalling the rule is a significant triumph for the industry.

The trucking industry has developed a strong relationship with Trump. Trucking officials met with Chao within hours after she took office, according to Chris Spear, the trade group’s president. Trump welcomed trucking executives to the White House by climbing behind the wheel of a Mack truck parked on the South Lawn in March.

“Your story is now being told to the highest levels of government,” Spear told his organization’s members in October.

DOT’s position on the speed-limiting software is that it isn’t dead but that the department has limited resources and higher priorities. No action is expected before the end of the federal fiscal year on Sept. 30 at the earliest.

Some rules that were in the works have been abandoned entirely. After four people died when a New York commuter train derailed while speeding around a curve in 2013, investigators determined that the engineer had fallen asleep. He had undiagnosed sleep apnea, a disorder that causes pauses in breathing and prevents restful sleep, and had made no effort to stop the train.

Safety officials blamed the crash on federal regulators for not requiring engineers to be checked for sleep disorders.