Big trucks need improved underride guards, trucking industry executives, government officials and safety activists agree, but opinions diverge sharply on the design and cost of the safety measures.

That’s what emerged from an all-day conference on deadly underride crashes at the Insurance Institute for Highway Safety’s Vehicle Research Center in Ruckersville, Va. Thursday.

Big trucks “are not in any way crash-friendly,” said Robert Molloy, director of highway safety at the National Transportation Safety Board.

Underride is when a passenger vehicle crashes into a semi-tractor trailer or a straight truck from behind or from the side and jams underneath, flattening the passenger compartment and injuring or killing the vehicle’s occupants. The term also describes what happens when bicyclists, pedestrians and motorcyclists slide under the body of a truck, usually from the side, and are in danger of being run over.

The industry should “move heaven and earth to make the best-possible protection,” said Marianne Karth.

Karth’s teenage daughters AnnaLeah and Mary, riding in the back seat, died from injuries in a 2013 underride accident. Karth’s Ford Crown Victoria was hit by a truck, spun, hit again and shoved backwards under another semi-trailer, flattening the rear of the passenger compartment.

Federal regulations require trailers and some straight trucks to be equipped with rear underride guards – the bars that hang down on the back of trucks and trailers. In fact, regulation requiring modest underride guards have been in place in the U.S. since 1953.

“It’s incredible that we have vehicles today that we can underride,” Molloy said.

The traffic safety community has resolved similar problems previously, he said.

As sport-utility vehicles became popular in the 1990s their high-riding stance increased damage to cars in crashes.

Regulators and the auto industry, he said, “were quick to act, and now we have vehicles that are more compatible.”

While acknowledging the truck problem, speakers at the roundtable differed on whether the guards should wrap around the truck or trailer, how much the extra weight might cut into payload, and how much the upgrades would increase cost.

The National Highway Traffic Safety Administration is considering a new standard for the guards – partly because of a petition from Karth – but some participants at the roundtable argued that the any likely regulation won’t go far enough to prevent more deadly underride crashes.

To demonstrate the problem, IIHS, an insurance industry trade group, crash-tested the latest-design Stoughton trailer, slamming a 2010 Chevrolet Malibu mid-size sedan into the back of the stationary trailer hooked to a semi-tractor and laden with 34,100 lbs. The test, which IIHS called successful, showed that the trailer’s new-design rear underride guard didn’t intrude into the passenger compartment, making the crash survivable.

The test was what’s called a 30 percent, where a portion of the driver’s side of the car smashes the underride bar.

The collision occurs at 35 mph, the speed at which federal regulations require that a vehicle is strong enough so that its occupants survive a crash.

Stoughton says the new-design rear bars will be standard starting late this year, but refused to provide a cost figure. The company did say the beefier bars would add very little weight, thus not cutting into payload capacity of the trailers.

The biggest change: Four supports across the horizontal bar, not just two. The new ones are on the outer ends of the bar, and all are fastened to a more robust undercarriage, Stoughton says.

As recently as 2013, only Manac had trailers with underride bars that passed the institute’s 30% offset crash test. Now, Vanguard, Wabash and Stoughton trailers also make the cut.

Trailers from Great Dane, Hyundai, Strick and Utility don’t past the test, the institute said.

One manufacturer said the fix is easy and not expensive. Moving the supports farther apart and strengthening the trailer floor to protect cars can be done for $20, and adds just 20 lbs., said Charles Dutil, president of Trailer-maker Manac.

NHTSA has said the fix is much costlier, averaging $2,000. IIHS disputes that figure as too high.

Regardless, the cost and extra weight – 60 lbs. was mentioned several times here — are unlikely to be undue burdens for independent owners-operators, said John Housego of Cary, N.C., who attended the roundtable. He owns a 2010 Freightliner semi-tractor, a 2015 Great Dane trailer and leases an older temperature-controlled trailer when needed for a job.

Housego said he’s willing to spend $1,000 or more on a rear underride-guard retrofit unit that would meet any new federal standard for the rig he owns, but not for a leased trailer.

He also agreed with industry representatives on a panel who said semi-trailer side skirts now used for fuel-saving streamlining could be made more rugged so they’d also serve as underride prevention devices in side crashes.

Panelist Robert Martineau, chief executive of Airflow Deflector, says his panels easily could be made sturdier to serve as crash bumpers as well as aerodynamic aids. He said he couldn’t say what the cost would be until he knows how much force such a panel would be required to withstand.

Officials from New York and Boston at the conference said they put side guards on city-owned trucks, such as waste haulers, and require companies that contract with the cities to install side guards to protect pedestrians, bicyclists and motorcycle riders.

Kris Carter, of the Boston’s mayor’s Office of New Urban Mechanics, said when that city began putting side guards onto city vehicles, “it averaged about $1,300 at rollout, the range for us in about $1,000 and $1,800, depending on the vehicle.”

There’s uncertainty over the seemingly straightforward notion of how many people are killed each year in all types of underride accidents.

Federal data from the widely used Fatality Analysis Reporting System logged 5,081 deaths from 1994 to 2014.

Yearly counts range from a low of 198 in 2001 to a high of 299 in 2002. The 2014 count is 228; 2015 data aren’t available yet.

But a September 2013 report from the Association for the Advancement of Automotive Medicine calculated that fatalities from one type of underride collision, the side-crash, are about three times as frequent as the federal data indicates. That’s why some critics are saying the federal data does not represent an accurate fatality count from all types of underride crashes.

The underride crash problem has been debated for decades. Back in 1991 NHTSA rejected extending requirements to prevent side underride crashes, stating, “Combination truck side underride countermeasures have been determined not to be cost effective.”