RALEIGH, N.C. (WNCN) – A gradual change in the weight and size of vehicles on the road is promoting a change in the way they are crash tested by the Insurance Institute For Highway Safety.  

In this latest round of tests, some of the most popular cars in the country didn’t fare so well when the institute updated the way it tests vehicles for side impacts. 

When it comes to side impact crashesinches can make all the difference. It all depends on how high off the ground your car rides.

The higher the vehicle rides, generally the better it fares in a side impact crash. These days, many vehicles ride lower — sometimes with 4-5 inches of ground clearance.  

The IIHS said that lower height is more problematic in a side impact crash with a heavy pickup truck or SUV.

“They are striking passenger cars at higher height on the door resulting in the likelihood of more intrusion and the probability of more injuries,’’ IIHS president David Harkey said. 

Here’s why injuries have increased. 

Over the years, pickups and SUVs have gotten bigger and heavier. That makes side impact crashes more intense. 

To improve its side impact tests, the IIHS built a heavier crash test vehicle, weighing 4,200 pounds. It strikes at 37 miles per hour. 

“This test is based on research we did early on, looking at real-world crashes,’’ Harkey said. 

The institute tested seven mid-size vehicles.

Only the Subaru Outback received a good rating. Two were acceptable, one marginal and three others, Toyota’s Camry, Nissan’s Altima and the Chevrolet Malibu, were rated poor. 

“The Chevrolet Malibu experienced significant intrusion into the occupant compartment,’’ Harkey said. “The structure of the vehicle simply did not hold up very well.” 

In addition to structural intrusion in the Malibu, Harkey said, “The side curtain airbag also only provided marginal protection from possible head injury.” 

CBS 17 asked Harkey what automakers need to do to survive the improved test and get a good rating. 

“In some cases, they may need to change the way the side curtain airbag operates within the vehicle,” he said. “In other cases, they may need to strengthen the door in some way.” 

The automakers have some time to do that as vehicles go through the next cycle of design changes.  

Starting next year, the institute said a “good” rating will be needed in a side impact crash test to meet its criteria for “top safety pick.” 

“I think we’ll see them respond immediately,” Harkey said. “They always strive to get those awards.”